Objective Reviews & Commentary - An Engineer's Perspective

March 1, 2012

ODAC Update

nwavguy-dscope-benchmarkODAC PROGRESS: As my articles have slowed to a trickle lately, hopefully these 5000+ words will be welcome news. After lots of professional and other distractions, I’m once again devoting serious time to the Objective DAC (aka ODAC). There’s been some good progress and I’m feeling better then ever about the ODAC’s performance. I’ve been comparing it with my Benchmark DAC1 Pre and it’s been eye opening in some areas. Keep reading for more details and further background on the ODAC design.

QUESTIONS (FAQ): Before you post questions or suggestions in the comments please have a look at the FAQ section below to see if your issue has already been addressed. I’ve tried to cover the popular questions and issues.

NOT FOR PROFIT: Please note I’m not selling the ODAC, just helping design it. Just as with my other projects, like the O2 portable amp, any profit from sales will be to whatever companies decide to have them made and sell them.

ODAC + ODA: The ODA, for those not following the history, is the Objective Desktop Amp. It’s essentially a future desktop version of the popular O2 portable amp with a few added features and upgrades. ODAC development is taking priority for now because the ODA will be partially designed around it. The ODAC can also be used with the O2 and as a standalone device.

FILLING A VOID: There are simply not many reasonably priced DACs supporting 24 bit operation over USB under Windows without needing proprietary drivers. While there are some low cost options on the market, at least some of them, such as the FiiO E10 and NuForce uDAC-2, offer barely more than 16 bit performance. There are even fewer options if you want a high quality 24 bit DAC with a low impedance output that can drive most popular headphones well (this leaves virtually all pro audio DACs out in the cold). The least expensive option I know of that’s been properly measured and performs well is the Centrance DacPort with the 1 ohm output upgrade. But it’s close to $500. Most DIY DACs, such as those from Twisted Pear and AMB, only support 16 bit operation over USB or they require proprietary drivers under Windows.

odac in o2 protoODAC + O2 RETROFIT: The ODAC fits neatly inside the O2 portable amp using the standard B2-080 enclosure by simply removing the batteries as shown to the right. One side sits in an enclosure slot while a mounting hole lines up with the central mounting hole on the O2 PCB anchoring the opposite side of the board. The battery terminals act as a “back stop” to absorb the force of plugging in a USB cable and the rear panel does the same when removing the plug. It worked out surprisingly well and I can’t take credit for this feat—my commercial counterpart came up with the idea and we mutually optimized the PCB layout to work with the O2. The retrofit requires a new back panel with an opening for the USB jack. At least one person has volunteered to design and hopefully sell a laser cut plastic panel for those wanting the O2/ODAC combo. Stay tuned for more but it’s a pretty simple retrofit that only requires soldering 3 wires at each end.

o2 off board input jack modificationO2 INPUT SWITCHING: Those who only want a USB headphone DAC (like the FiiO E10 or NuForce uDAC-2) can simply wire from the output header of the ODAC to the P1 input header on the O2 board. But for those who still want to use other sources (like an iPod, etc.) with their O2, you can have your cake and eat it too. Once you cut the traces shown to the right you can wire the ODAC to terminals 3 and 4 of the input jack. These lead to internal switches in the jack and will connect the ODAC only when nothing is plugged into the O2.

ODAC STANDS ALONE: If you just want a DAC with no preamp or headphone amp, the ODAC can be used by itself as a USB powered 24/96 DAC. Because it supports 24 bit operation over USB there’s little or no penalty using only a software volume control or you can control the volume downstream of the ODAC. The board measures about 49mm x 58mm (1.9 x 2.2 inches) and will fit in many small enclosures such as the Box Enclosures B1-080. There are also several inexpensive eBay DIY enclosures that would work. Ignoring the output jack, it’s only about 4mm in total thickness as it’s entirely a surface mount design This allows it to easily “piggy back” on top of other boards, etc. In the O2 tradition, it has three mounting holes (geeks know 3 points determine a plane and 4 just mess things up ;). The components are also held back from two opposing edges for slot mounting. There’s a provision on the board for a 3.5mm stereo output jack that’s on the same edge as the USB connector requiring only one machined (or laser cut) panel. DIYers can also panel mount 3.5mm or RCA output jacks or simply build the ODAC into other gear. The ODAC can be connected to any input that accepts standard Redbook 2 Vrms line level audio and has at least a 10K input impedance.

O2 DESIGN PRINCIPALS APPLIED – The O2 was implemented using well proven design techniques and countless rounds of measurements and refinements. The result is performance well beyond what most would expect from the O2’s modest and inexpensive components. The O2’s popularity has shown this design methodology is valid. Put simply, the O2 has proven far greater than the sum of its parts. I applied the same approach to the ODAC design. While it uses relatively modest components, it delivers performance well beyond what most would expect given the cost and components used. The ODAC closely follows the chip manufacturer’s reference design information and has been carefully optimized through several iterations. Using a professional mixed domain audio analyzer, like the Prism dScope, enables a level of performance refinement that would otherwise be all but impossible. This gives the ODAC a huge advantage over most DIY DACs and products from small manufacturers lacking proper test equipment.

THE AUDIO ANALYZER ADVANTAGE: To make meaningful measurements of a DAC you need an ADC with a noise floor significantly (at least several dB) lower than the DAC’s noise floor. Otherwise you’re measuring the ADC as much (or even more so) than the DAC. Such an ADC is increasingly hard to find once you get up to Benchmark DAC1 levels of performance. The Prism Sound dScope, however, has a noise floor of just over 1 microvolt or around 126 dB below the Redbook standard of 2 volts. Even my $1800 Benchmark ADC1 can only manage a best case 119 dB and less expensive audio interfaces are typically significantly worse. It’s also extremely useful to have an audio analyzer capable of real time mixed (analog and digital) domain generation and analysis. A product like the dScope, or a high-end Audio Precision analyzer, is about the only way you can properly measure and develop a high performance 24 bit DAC. Otherwise the true performance is masked by the ADC you’re using and the limitations of using PC software that cannot do anything in true real time because of the PC’s operating system. Input isolation is also a significant issue. Using RMAA typically requires sharing the DAC’s USB ground with the ADC’s ground which, in itself, can create all kinds of erroneous results and ground loops. Properly testing a high performance DAC requires more than just another PC audio interface. You need specialized hardware designed for the purpose.

THE OTHER WAY: Lots of DIY, and even some commercial DACs, seem to be little more than a few trendy popular chips slapped onto a nice looking PC board. If their designers conducted the proper measurements along the way, where are their published results? You generally have to look at expensive products like those from Centrance, Benchmark Media, and Anedio to find meaningful DAC measurements. Some designers and companies simply quote highly misleading specs from the DAC IC datasheet but, as I’ve shown in my reviews, the results often fall far short. A good example is the FiiO E10 that only delivers roughly 16 bit performance even running at 24 bits. Some companies, like NuForce, Audio-GD, and Twisted Pear, argue they “design by ear” but the unavoidable human bias associated with such sighted listening is well documented.

IT’S ABOUT WAY MORE THAN THE RIGHT PARTS: Using high-end parts is meaningless if the implementation is (often unknowingly) flawed. It’s like putting a Ferrari engine in a Yugo or using ultra fast RAM in a PC with a slow processor and chipset. It’s pointless. Just as cars are defined by far more than just their engine, and PC performance depends on several subsystems all working well together, the same is true of audio gear. The best products are from manufacturers that conduct proper testing and have the resources and desire to sweat all the little details rather than just using the latest FOTM parts and making it look nice.

FOLLOW THE PROFITS: Sadly a lot of “specialty” audio designers and companies seem to depend mainly on subjective hype and sighted listening bias, rather than proper design and objective performance, to sell their products. One can argue some are mainly trying to cash in on the latest FOTM craze rather than investing the time and money to design genuinely solid gear. It’s one of the goals of this blog to help not only expose half baked designs for what they are, but also demonstrate better alternatives don’t have to be be expensive or made with dual phase aligned unobtanium.

SMALL CHANGES CAN EQUAL BIG IMPROVEMENTS: I’ve sometimes been amazed how even small changes have made fairly large differences in the ODAC’s performance. Several of the ODAC’s optimizations run counter to typical DIY audiophile beliefs. Here are a few examples of typical design myths:

  • Larger Value Capacitors Are Better – “Upgrading” certain power supply capacitors to larger values made the ODAC perform significantly worse compared to using the values specified in the chip manufacturer’s reference design. Bigger value caps often have higher ESR, more inductance, and much higher impedance at very high frequencies. They can also create other problems.
  • Top & Bottom Ground Planes Should Be “Stitched” Together – Stitching is the practice of applying a board-wide grid of small vias (plated through holes) that connect the top and bottom ground planes. Some argue this lowers the ground impedance and keeps ground paths shorter. But they’re not true ground planes on a 2 layer board. Instead you have a bunch of ground fill areas isolated by signal and power traces. When you have these “ground islands” rather than a true continuous ground plane, the stitching can easily create undesirable ground loops and send ground currents where you don’t want them. I’ve seen several DIY and commercial designs ignore this issue and other proper grounding practices.
  • Expensive Audiophile Dielectric Capacitors Work Best – I experimented with various types of poly film caps, including audiophile preferred SMT Polyphenylene Sulphide (PPS) types, and found they sometimes made things worse. I also discovered not all ceramic caps perform equally. There’s no simple rule of thumb that always works. You have to make the right measurements and sweat the details. It’s time consuming but proved worth it. Every capacitor associated with the DAC chip and analog circuitry of the ODAC has been carefully optimized using the dScope. Overall, my capacitor tweaking resulted in lowering the noise and distortion by more than 6 db. And, trust me, the final result is not what your average DIYer would intuitively think is best.
  • Fully independent Analog & Digital Power Supplies Improve Performance – While there are probably a few high-end DACs that measure slightly better with fully independent digital and analog power supplies, the reality is the DAC chip itself and related digital noise is more likely the dominant limiting factor. I’ve shown, with multiple measurements and tests, the power supply is not holding the ODAC back in terms of performance. And while there’s some carefully designed filtering and ground routing between the analog and digital sections, they’re both derived from the same source. A DAC will only perform as well as its weakest link allows. In an optimized design that weak link is usually the DAC chip and/or a certain amount of unavoidable noise from the USB and I2S digital buses. When that’s true, adding more esoteric power supplies won’t help much if at all.

PCB LAYOUT IS EVERYTHING: I can’t stress this enough. Just as the O2 board was designed for “function over form” so was the ODAC. Many DIYers and audiophile manufacturers want to show off their PC boards. So they often lay them out at least partly to look nice. That almost always means the performance suffers. In the case of a 24 bit DAC I’ve learned it might suffer quite a bit. Keeping the noisy digital signals out of the analog side of a DAC becomes challenging once you get past about 17 bit performance. And for those trying to judge if they got it right by using RMAA and a sound card, or an 8 bit oscilloscope with only 40 dB of dynamic range, good luck with that (see The Audio Analyzer Advantage above and my RMAA article for why). And good luck using typical sighted listening tests to verify a PCB layout.

BENCHMARK DAC1 REFERENCE TARGET: The Benchmark DAC1 models have been widely reviewed and praised—especially for their excellent measurements, sound quality, and hassle free 24 bit high resolution USB support. Hopefully many agree the DAC1 Pre is a worthy reference target to judge the ODAC against. While it’s a bit like putting a Mazda MX5 Miata up against a Porsche 911 it’s still a worthy goal. When I present the ODAC’s final measurements I’ll show many of the same results for the Benchmark and everyone can judge the end result for themselves. I’ll also be comparing the ODAC to the FiiO E10 as it’s probably the ODAC’s closest current 24 bit USB competitor in terms of cost and might even include a few pro audio interface results as well.

PRELIMINARY BLIND TESTING: In preliminary blind comparisons between the ODAC prototype and my DAC1 Pre, they sound the same. I’ll be doing more involved blind tests, but the initial results are very promising. If this trend continues I’ll be adding an “ODAC Public Blind Challenge” to my existing O2 and op amp blind challenges. If someone thinks they have a DAC that measures well and sounds better, let’s find out!

DESIGNED AND (for now) ASSEMBLED IN THE USA: This may not matter to everyone, but living in the USA myself, it’s something I take at least some pride in. Steve Jobs famously told President Obama “those jobs are not coming back” referring to Apple making nearly everything in China. And while Apple products are generally made to a high standard in China they’re still designed in the USA. The same cannot be said for a lot of reasonably priced “boutique” audiophile gear. NuForce, Audio-GD and FiiO are a few examples with well documented, and sometimes embarrassing, problems. And, based on what I’ve seen, a lot of the gear being sold mainly on eBay and direct out of Asia can be even worse.

USB POWER ADVANTAGES: A self powered DAC that operates entirely from USB power has a number of practical advantages:

  • One Size Fits More – Because the ODAC needs to be commercially assembled in volume using automated equipment it’s much more cost effective to have a single version that works in the O2, ODA, standalone, and can be added to other DIY or commercial designs. USB power is virtually required to make this possible. Higher volume manufacturing of a single board brings the price down for everyone.
  • O2 Compatibility - The O2 has a dual +/- 12 volt power supply delivering around 200 mA peak to each channel of the amplifier. The ODAC requires around 125 mA at a far lower voltage. The O2 cannot power a high quality DAC without adding a switching regulator or DC-DC converter which would add noise and still tax the O2’s power supply. There’s also no physical room for the added hardware. So USB power is the only viable option for the ODAC in an O2.
  • Stand Alone Operation – For those wanting to use the ODAC by itself, USB power has a clear advantage. It eliminates the need for another power supply and is especially desirable for portable use.
  • No Enumeration Problems – Some USB interface ICs are designed to be USB powered. They will not enumerate correctly with the host device if they’re already powered when the USB connection is made. This can necessitate using USB power for the interface chip while using a different power source for the DAC chip. This creates various other challenges including the next point.
  • No Unpowered Inputs - USB power also simplifies problems associated with having unpowered IC’s connected to powered ICs. Digital ICs that are not powered don’t generally like being connected to ICs that are. It can result in a potentially destructive condition where the normally high impedance inputs of a powered IC represent a low impedance when the IC has no power. The powered IC pumps abnormal levels of current into the unpowered inputs. When power is applied with the IC in this invalid state it can “latchup” and draw large amounts of power supply current destroying itself. Some of the solutions to this problem can degrade jitter performance because the I2S bus is subject to this issue on a USB DAC with a split power scheme. Powering the entire DAC from USB power neatly solves these problems.

USB POWER CHALLENGES:  USB power also presents some challenges:

  • Potentially Greater Noise -  USB power is more of an unknown compared to a dedicated power source. So it requires extra filtering and careful design to avoid degrading the performance of the DAC. This is especially true when you’re aiming for much better than 16 bit performance. The USB powered FiiO E10, Creative X-Fi Go, and NuForce uDAC-2 all promise 24 bit performance but only deliver around 16 bit performance. Likewise, when running from AC power, the latest MacBook Air also fails to deliver better than 16 bit performance from its 24 bit DAC due to extraneous power-related noise.
  • Audio Output Voltage - USB power can be as low as 4.5 volts, and when you add in losses from power filtering and the DAC/op amp circuitry, you’re lucky to get 4 volts peak-to-peak of output swing without clipping. That works out to 1.4 Vrms which is a significant 3 dB shy of the 2.0 volt Redbook standard for digital devices. That’s 3 dB of potential dynamic range lost and a 3 db drop in level compared to normal home sources (like a CD player, network media player, etc). Indeed most of the USB DACs I’ve tested, and even popular DIY DACs like the AMB gamma, have this shortcoming.
  • Capacitor Coupled Outputs - A single-ended DAC power supply usually requires an output coupling capacitor to block the 1/2 Vcc voltage at the DAC output. Such a capacitor, to drive a 10K load, needs to be a fairly large value to avoid low frequency roll off and excessive phase shift. It also should be a high quality film, rather than electrolytic, type. But many USB powered DACs, in the interest of saving money and space, use electrolytic or otherwise compromised output capacitors. This is even true of some audiophile DIY designs like the AMB gamma.
  • Power Related Jitter - Power and ground “pollution” at various frequencies can have a significant impact on jitter performance. Noise from the power supply can, in effect, modulate the digital bit stream creating jitter.
  • USB Maximum Current Limit - While the USB ports on any PC or laptop made in the last 6+ years can nearly always supply 500 mA of current there are some exceptions. There are a few ultra low power netbooks that have 100 mA USB ports and unpowered USB hubs are also, at least in theory, limited to 100 mA per port. I’m not sure about iPads and Android tablets but I suspect they may be rated for only 100 mA as well.

ODAC POWER DESIGN – The above challenges can be largely or entirely overcome with careful design and by using the right components. Here’s how the ODAC addresses them:

  • Power Noise Below the DAC’s Noise Floor – It turns out ground and conducted (electromagnetic) noise are typically as significant as noise on the USB power line. Because a connection to the PC’s ground is required regardless, simply using an external power supply doesn’t automatically mean freedom from USB bus noise. With the ODAC the solution involved careful routing of ground currents, different power supply conditioning for the digital and analog sides, careful capacitor selection, and inductive filtering. The result is the latest prototype’s noise floor is mainly determined by the DAC IC itself not the USB power bus. Put another way, an independent power supply wouldn’t make much difference.
  • Redbook Standard Audio Output Voltage – The ODAC delivers delivers the Redbook standard output of 2 Vrms without clipping by using a bipolar power supply. This alone adds roughly 3 dB of dynamic range to the ODAC’s performance compared to many USB powered DACs.
  • Direct Coupled Output – The ODAC uses a ground referenced split supply so no virtual ground or output capacitors are required. This assures accurate low frequency amplitude and phase response with no bass roll off and avoids potential capacitor-induced distortion.
  • Power Related Jitter – The ODAC’s power filtering was optimized not just for the best noise and distortion performance but also for the lowest jitter. Interestingly some of my attempts at filtering did help lower the power supply noise but increased the jitter. The dScope’s J-test proved invaluable in optimizing the PC board layout and power supply design for simultaneously low jitter and low noise.
  • USB Current Limit – I’m not aware of any 24 bit USB interface and high performance DAC ICs that, combined, come in safely under 100 mA total. The bipolar power supply that allows a 2 volt output does require a bit more power. And the choices in 24 bit interface chips are very limited. The only way to keep the total budget under 100 mA would involve a much lower performance DAC and that’s not an acceptable trade off. The good news is I’ve tried the ODAC on many PCs, including two netbooks, and it works fine. It even worked on an unpowered USB hub despite being slightly over the 100 mA limit.
  • Worst Case – If someone does encounter a USB port that is either extremely noisy or can’t provide 125 mA of current, the solution is simply to use a powered USB hub. They can be purchased for as little as $20 or so.

SO HOW QUIET IS IT? Using the industry standard A-weighted dynamic range test with a –60 dBFS signal, the current ODAC prototype has an impressive 112 dB of dynamic range. How good is that? My $1600 Benchmark DAC1 Pre, on the exact same test referenced to the same 2 volts, is slightly worse at 111 dB. CD quality audio, in comparison, has only 96 dB of dynamic range. I should note if you have an application where you can use the DAC1’s full 7+ volts of output, it can manage 116 dB of dynamic range referenced to it’s maximum output. So you do get something for your extra $1500.

ENOB: ENOB stands for Effective Number of Bits and is another measure of a DAC’s performance. No 24 (or 32) bit audio DAC can achieve true 24 bit performance, In fact, 20 ENOB is generally considered the “Holy Grail” of real world DAC performance. The ODAC is just under 19 ENOB and the Benchmark, even referenced to its full 7+ volt maximum output, is 19.3 ENOB. The FiiO E10, even in 24 bit mode, is only 16.2 ENOB.

DISTORTION: The ODAC prototype on a standard –1 dBFS 1 Khz signal has about 0.003% THD+N while the Benchmark DAC1 is only slightly lower at 0.0025%. The ODAC, on every distortion test I’ve run, is well below my ideal 0.01% maximum THD+N. That’s true even at 0 dBFS which wrecks havoc with some DACs (like the NuForce uDAC-2). The ODAC’s performance does not noticeably degrade in any way at 0 dBFS so I can officially certify it Lady Gaga compatible (scroll down to Lady Gaga In Audacity here).

JITTER: You can’t put a single number on jitter performance but I’m quite happy with the ODAC’s results so far. It can’t match the expensive ASRC jitter reduction used in the Benchmark DAC1 but it’s significantly better than most DACs, including the FiiO E10, and several of my pro sound audio interfaces. The ultimate proof will be in the blind listening tests.

IT MAY GET EVEN BETTER: It’s a bit like peeling an onion. As you improve one area of the design, the lowered noise and distortion reveals other areas that can benefit from refinement.While there was some hope the version on my bench now would be close to the final production ODAC, we’ve decided to go one more prototype iteration and incorporate several more incremental improvements. Some of those changes may improve the performance still further but it’s hard to know by how much. When it’s all said and done there will be at least 4 generations of ODAC PC boards. Despite the more than acceptable performance of the current prototype we’re not done chasing the Benchmark DAC1 yet.

FAQ (please have a look here before posting questions!)

WHAT WILL THE ODAC COST?: The ODAC is still on track to hopefully come in under $100 for a completely assembled, programmed and operational board ready to slip into an O2 or the upcoming ODA. If you want a standalone DAC you have to add at least a few bucks for an enclosure, panel and output jack. We won’t know the final pricing until the production design is bid out for assembly.

WHEN WILL THE ODAC BE AVAILABLE? Given we have another prototype cycle ahead of us the best case is likely late April if all goes reasonably smoothly. But that could slip into May or even later if there are unforeseen problems.

IS THERE AN OFFICIAL ODAC FORUM THREAD? Not yet but I’ll post an update as soon as there is.

CAN I BUILD MY OWN ODAC? Unfortunately no. The ODAC will be offered only as an assembled board. Please see the next question. (PS – You probably wouldn’t want to anyway. It has a lot of 0603 components which are really tiny and a fine pitch quad IC package which are no fun to work with).

WHERE IS THE SCHEMATIC & PARTS LIST? As explained in the first ODAC article, there are no DIY-friendly 24 bit USB audio chips that meet the design criteria. So we’re forced to use components licensed for OEM use that are not available through normal distribution. Even the datasheets are marked confidential and access to the interface chip requires signing an agreement. Given the ICs have to be purchased direct from the manufacturer in substantial minimum quantities it’s not reasonable to expect someone to make a substantial initial investment only to undermine them by giving the same design to other commercial interests. It would be a bit like designing a new car for Ford and then saying “oh by the way we’re also giving this to the Volkswagen Group, General Motors, and anyone else who might want it. You better hope there’s enough sales volume to divide between all of you.”  Having the ODAC be an open source design would only increase the financial risk and the end result could easily be a “chicken and egg” situation. Everyone might choose to wait and see who else might choose to produce the DAC. And, regardless, individual DIYers can’t get the required parts anyway. Hopefully everyone can understand it’s only fair the person taking all the initial risk, and spending the money up front, should not have the rug potentially pulled out from underneath them by sharing the same design to anyone with the commercial means to produce it.

WHAT DAC AND INTERFACE CHIPS DOES THE ODAC USE? For the same reasons we’re not releasing the schematic, we’re not yet releasing certain other details yet either. Please see the question above.

IS THE ODAC BASED ON THE XMOS USB INTERFACE? No. The XMOS solution requires a proprietary Windows driver that must be licensed for a fee. We also don’t believe the XMOS chip offers any real world benefits in this application. See the next two questions.

IS THE ODAC USB AUDIO CLASS 1 OR CLASS 2 COMPLIANT? The ODAC is USB Audio Class 1 (UAC1) compliant because it’s the only standard that allows native 24/96 support in Windows, OS X and Linux without any special drivers. USB Audio Class 2 (UAC2), while newer, offers no meaningful advantages for 2 channel audio playback and is not yet natively supported in Windows. Its main benefits are for multi-channel audio and recording at 24/192. Some of the best performing DACs available at any price are UAC1 devices (including the Benchmark DAC1 series).

IS THE ODAC ASYNCHRONOUS There’s a lot of marketing and other hype lately surrounding asynchronous DACs. Much of it is myth. Just like op amps got a bad name from the old 741 released many decades ago, so did USB audio based on early synchronous designs. But most modern USB audio devices use an adaptive interface where a local clock controls the DAC and is only loosely coupled to the PC’s timing. Contrary to popular belief, with an adaptive interface the data is not directly clocked by the USB port. This method has been refined over the years and can work very well. It’s also natively supported by all major operating systems. Most methods of true asynchronous USB audio require proprietary drivers under Windows and proprietary drivers are rarely a good thing. Judging a USB DAC by whether it’s asynch or adaptive is a bit like judging a car by the engine configuration—i.e. an inline six in a BMW vs a V6 in a Nissan GT-R. Other aspects of the design are more likely to limit the performance and there are plenty of examples of outstanding USB DACs using adaptive interfaces.

WHAT DIGITAL FILTERING DOES THE ODAC USE? Another trendy DAC topic is the type of output filter. It’s mostly about chip and DAC marketing types dreaming up added ways to differentiate their products. But, ultimately, what matters most is the measured performance at audible frequencies and listening tests using proper blind techniques. Judged by those criteria, I’m not sure either filter has an overall advantage. I have not seen any credible blind listening tests that support one filter type sounding better than the other. The ODAC, like many great DACs, uses a linear phase filter. Just like with asynch vs adaptive, there are many other variables that determine the overall performance. You have to consider the entire product as a whole. It’s foolish to dismiss a BMW or Porsche because the engine cylinders are not arranged in a “V” because, ultimately, that’s only a small part of a much bigger picture.

WHAT AUDIO FORMATS DOES THE ODAC NATIVELY SUPPORT? The ODAC supports 44, 48, and 96 Khz each at 16 or 24 bits. 24/192 is not natively supported by Windows over USB, nor does it offer any audible advantages for audio playback (in fact most DACs that support 24/192 perform worse at 192 Khz than at 96 Khz).

ARE YOU PLANNING TO MAKE MONEY OFF THE ODAC? No. I will not get any money from ODAC sales. Someone else is taking all the financial risk and coordinating all the manufacturing and sales logistics. If the ODAC proves popular, any profit is rightfully all theirs. Frankly, given the 4+ design iterations, steep minimum order quantities, and all that’s gone into it so far, they might be lucky to break even. But it’s ultimately no different than JDS Labs and Epiphany making a profit selling the O2. For me this remains an entirely not-for-profit blog and endeavor.

WHERE ARE THE MEASUREMENTS? Given the performance may change (hopefully for the better) with the next iteration it would be a lot of wasted work to publish detailed measurements and graphs only to do it all over again once we have the final design done. I made that mistake with the O2.

WILL THE ODA BE OPEN SOURCE? Yes it will. The ODA will be just like the O2, and anyone who wants to sell the ODA + ODAC can likely negotiate buying assembled ODAC boards with some sort of quantity discount. They might even want to weigh in before the initial production quantity is determined.

WHY NO S/PDIF INPUT? I know there have been several requests for S/PDIF, but as was explained previously, it’s not a trivial or even logical addition. To summarize, here’s why:

  • O2 Compatibility – Having the ODAC fit inside the standard O2 is a pretty cool thing. O2 compatibility seems to have more interest than S/PDIF support. It would be very difficult to add an option for S/PDIF and still have the ODAC fit in the O2. If it’s even possible with a 2 layer board it would require components on both sides which would substantially raise the price for everyone. And it would likely have inferior performance due to a less than optimal PCB layout. Likewise splitting the ODAC into two different boards would also raise the cost in multiple ways.
  • S/PDIF Doesn’t Fill a Niche – There are lots of 24 bit capable S/PDIF DACs as it’s much easier and cheaper to implement compared to 24 bit over USB. Even the $25 FiiO D3 does 24 bit over S/PDIF. But there is a shortage of reasonably priced 24 bit USB DACs. See Filling A Void near the beginning of this article.
  • No Native Support - There are very few suitable 24 bit USB audio compliant (i.e. driverless) interface ICs available. Likewise there are not many relatively high performance DAC chips that work well in a simple 24 bit USB DAC design without a microcontroller. The chips used in the ODAC lack native support for an alternate S/PDIF or second I2S input and the lack of a microcontroller complicates things further.
  • More Jitter – Adding an S/PDIF input option would mean “breaking” the I2S bus between the USB interface and the DAC to allow the insertion of an S/PDIF interface and/or switch. Ideally, for lowest jitter, you want to keep the I2S routing as short, clean, and direct as possible. With the current PCB size adding S/PDIF could easily compromise the jitter performance.
  • Possible Future Version – There is more room in the ODA and it’s possible there may be a more expensive version of the ODAC someday as a “plug and play” replacement for the current ODAC. Such a DAC would likely use more expensive components and possibly a 4 layer PCB raising the performance bar even higher and could also more easily include an S/PDIF input. That way the cost is kept as low as possible for the mainstream version and those who want more can pay more. I also expect some better 24 bit USB audio interface ICs to come on the market compared to what’s available now. Some might even more DIY-friendly and suitable for an open source design.


  1. Great work nwavguy! Hope to see the ODAC coming out soon!The ODAC sounds like a DACport on steriods. Great to see for the first(I think) time someone not talk about the DAC they are using and spend the time to get the implementation right.

  2. Great work as always, NwAvGuy. We look forward to the final design!

    We'd be glad to bid on the assembly job (15k board/day capacity). You have my contact info...


  3. If you manage to get it out before summer I will be (one of) your first customers. However, the ODA is where I get really excited.

  4. I'm glad your not selling this dac b/c i would be forced into skepticism at your AWESOME claims.
    Just like it was/is with the O2, its very hard to trust any other companies after reading your posts. You simply take things to another level.

    I cant wait to get my hands on the O2/ODAC combo. Awesome work!!

  5. Sounds like the ODAC will have an awesome price/performance ratio! The one thing that bugs me is the linear phase filter... I hope the phase deviation is not too much. I think it's pretty well accepted that spatial information is encoded as phase in audio waveforms.

    1. Linear phase filters create LESS phase shift in the audio band than minimum phase filters do. A minimum phase filter trades off more phase shift for less pre-ringing. And yes phase is responsible for spatial perception, but it's predominately interchannel phase information. In terms of interchannel phase shift, the ODAC is perfect. In terms of intrachannel phase error (where both channels are phase shifted equally) the linear phase filter in the ODAC has an advantage over minimum phase filters.

  6. NwAvGuy,
    Greetings and good tidings to you and yours! Whew! A nice read as always. I don't think enough can be said of your positive contribution to the headphone listening community. It's high time the snake oil vendors were rooted out and shown for what they are. While there may be a market for nearly any type of kit, people should know exactly what they spend their money on so they can at least make an informed decision. The FiiO E10 or Creative X-Fi Go may be all someone can afford but at least they should know the real performance. Your blog is a beacon that so many have come to trust, myself included.

    When I was working in the loudspeaker side of the audio industry, the company I was with had substantial interest in a Chinese factory in Guangzhou. All the design and proto work was done in our offices and lab in Santa Monica, Ca. We shipped cones, surrounds and suspensions from Germany to "our" factory in China, where we had our own employees doing the QC and providing assembly technique instruction. Our products won many prestigious awards, so I can attest that being "Assembled in China From Foreign and Domestic Parts" should dissuade no one. It all matters who does the proper proto design work and testing. I take pride in "Made in America" but there are other countries that do excellent work as well, I might add.

    I am so looking forward to building the ODA/ODAC and being able to trust it's performance. However, I can't wait until they are released before building even more O2's! They just ROCK! The more I listen the more my cheeks hurt from grinning so much! I just took a job building a sound booth for internet radio/podcasting and need the O2's (4) to replace h.o.'s on some Digi boxes (33Ω). If you're interested, I may have a 19" rack-mount faceplate for dual/quad O2's that you can post for others who may need such a thing.

    BTW, under the FAQ I found some grammar you may want to edit: "...making a profit selling the O2. For my this remains..." should be "me". Also, the link to the Lady Gaga CD import I believe is Audacity not Audigy.

    Cheers and 2 THUMBS UP!!

  7. Nice read and well written!

    But without open hardware design I will go with the HA-Info U2 Plus, it has a S/PDIF, line out and headphone out for not even 80 bucks delivered to Europe. And i did not have heard any complains about it. If I dont like the headphone out i can still plug it into the O2, which is great btw.

    1. I haven't tested the U2 Plus, but I have tested an earlier HA-Info headphone DAC and it's a train wreck. HA-Info used a DAC IC that requires a microcontroller to configure the digital filtering for different sample rates. But there's no microcontroller. So the DAC chip is always "stuck" in 24/96 mode. It does indeed work reasonably well at 96 Khz, but at 44 Khz (which is 99% of digital music) it has horrible alias problems because the digital filter is set up with a cutoff frequency that's far too high (48 Khz vs 22 Khz). In practice this means it has an unacceptable level of distortion at high frequencies.

      The AC power adapter it came with also has an unacceptable amount of leakage current to the AC 120 volt line. It's literally a safety hazard and would never pass any safety agency approval like CE or UL despite having a CE mark. China is famous for marking products with the "CE" logo that have never been tested for CE compliance. When they're caught they claim "CE" stands for "China Export". See: http://en.wikipedia.org/wiki/CE_mark#China_Export

      The HA-Info DAC I have is a perfect example of trendy popular chips being slapped on a nice looking board with little regard for the actual performance. They likely know most are not going suffer the costs and paperwork to return their products from another country. They also, like so many similar companies, are relying on subjective listening bias to gloss over the flaws in their products. In the case of HA-Info it's also possible, as happened with NuForce, they're not even aware of the flaws as they may not even perform any proper testing.

      Finally, the HA-Info products are not open hardware designs either. But it's certainly your choice. If you can get the E10 for around the same amount at least you know what you're getting there. With HA-Info you really have no idea.

  8. Hah and I was just looking at a bunch of other DACs when I saw this post come out....I guess I'll be waiting for this guy...
    Some of the other DACs I was considering were:
    Emotiva XDA-1 (only $250 right now)
    HRT Music Streamer II
    CEntrance DACport LX
    I just wish there were measurement datasheets for all of these....it's so hard to decide what to plunk down money on...

    1. The Emotiva won't do 24 bit over USB. The HS MS II is a decent DAC for the price. The DACport LX should comfortably outperform both of them but is relatively expensive. Stereophile has tested the DACport.

    2. I would, personally, reccomend the HRT MS2. Based on my listening, it's very much worth its price. I also wish there were measurements.

  9. What can we say? Fantastic work, NwAvGuy! Eagerly waiting to build my ODAC after having built 2 O2.

  10. Awesom !!!!! Are you taking any Pre-orders???

  11. I am so excited. Thank you NwAvGuy for your continued efforts on this project. I have noticed that when using the usb input on my sparrow there is some odd "lag" when swithing between songs in Foobar. Is this caused by the inherent differences between usb and spdif, or is it software related? I chose to use spdif because of the 24bit support and the seemingly "smoother" transition playback. Does this have any effect on quality?

    1. I'm fairly happy with the ODAC's mute timing and I use Foobar. But it is a trade off with most DACs. If the muting delay is too short you may hear a "tick" under some circumstances when the DAC first receives a new bitstream. If it's set too long the DAC may audibly clip off the first tiny bit of the bit stream. I plan to do more testing in that area and make sure the ODAC mute timing is as optimal as possible. This is something a DIYer could change by replacing one SMT resistor.

  12. In the "USB Power Challenges" section you speculated about the USB current limits for devices attached to iPads and Android tablets. The release of iOS 4.2.1 changed the limit for iPads from 100mA to 20mA. This is a shame because the combination of battery powered O2 + ODAC + iPad (and 96/24 or 44/16 ALAC files) would be an extremely portable audiophile-grade setup. The iPad will play USB audio when used with the USB accessory kit. An article @ Benchmark's site details this well:

    iPad Streams High-Resolution Audio to DAC1

    I am not certain what other tablet manufacturers limitations are. There is talk in the Apple development community that this restriction will be lifted. Hopefully this will be the case. Until then a powered USB hub would have to be added to the mix.

    1. Thanks for the info. Hopefully a powered USB hub solves the problem but I haven't verified that.

      I really can't blame Apple for their decision and it might be a requirement as I'm sure the iPad has a rather critical "internal power budget". The USB port can't run from raw Li-Ion battery power. It's powered from a switching converter/regulator that's probably also powering other subsystems within the iPad. The efficiency is highest when they're running close to their design limit so in the interest of maximum battery life (an extremely critical design parameter for tablets) the hardware engineer should try to hit that efficiency "sweet spot" with little excess capacity. Exceeding the 5 volt supply's current limit may also completely crash the iPad depending on what else it's powering.

      Apple could, if they wanted, design a future iPad with more external power available. We'll have to see if the iPad 3 this month changes anything. Personally I like the idea of an open source network music player based on something like the Raspberry Pi + ODAC with Android and iOS apps for the user interface. :)

    2. Really loving this integration idea that.

      Of course, any apps written for android and iOS devices would also have to be open sourced so as to be in the same vein as of the project ;)

    3. My initial thought about the lower current limit for iOS 4.2.1 was that Apple was simply trying to protect users from being "surprised" by decreased battery life caused by connecting power hungry USB devices. However, your points about engineering related issues are very likely the driving factor.

      I like the direction of your thought regarding the Raspberry Pi feeding the ODAC. Despite its low price tag the Raspberry PI seems like overkill depending on what you are intending to do with it. My assumption is that you would simply like to feed the ODAC over the network via an app on the tablet. The Raspberry PI has many more design features than that (hardware video decoding, SD card slot, HDMI interface etc). And unfortunately the board also lacks WiFi so you would need to colocate ODAC and the Raspberry-PI near an Ethernet connection.

      A project I may take on personally once you ship the ODAC is to implement Apple's Airplay protocol using a low-cost/power and application appropriate ARM or ATmel chip plus a wi-fi module. IOS devices will send an ALAC encoded 96/24 file over AirPlay, which the ODAC should appreciate. The idea here is to create another small PCB-based module, much like the ODAC that could be connected to or housed with the ODAC board and allow people to create affordable audiophile-grade network DACs that could be used to front-end any system desired. Companies like Denon are already building AirPlay compatibility into their AV receivers, it would be nice to have an open source implementation as well.

      The AirPlay protocol has been reverse engineered a few times and details about that can be found here: AirPlay Info. Doing it in an embedded environment should not be too difficult.

      Supporting other kinds of tablets could be easily done by just using existing third party client implementations as detailed in the above link.

    4. As I said in my February article, I'll be happy to lend some hardware support on the DAC/analog/power supply side of a network player if someone else can sort out the rest. Reverse engineering Apple proprietary protocols scares me personally and there's always the chance Apple will decide to change it and break whatever you do. They've been constantly doing just that to try and thwart jail breaking, etc.

      And I agree a low cost platform with WiFi already on board would have some advantages. But any suitable ones I know of cost more than the Raspberry. Plus sending lossless audio over WiFi can be a bit sketchy in many installations depending on the distance, quality of the router, etc. You turn on the microwave oven and the sound starts dropping out. But clearly it's a desirable feature for many. Something like this is relatively expensive and lacks the internal space for the ODAC but would otherwise make a nice network player:


      I haven't looked very hard but I would think someone, somewhere, is already at least part of the way down this road by now using off the shelf hardware running Linux and an iOS and/or Android app?

    5. In principle, the microwave need not cause audible errors for WiFi streaming. The devil is in the details, though.

      In networking, you can use "TCP/IP" or "UDP/IP". TCP will detect errors in transmission, and retransmit lost packets. UDP is simpler and thus has less overhead. UDP also allows "multicast" where one device broadcasts data and any number of devices can receive the data (and play the song).

      The amount of data even a lossless stereo stream requires is much much less than the maximum you can transmit over WiFi. So I think it should be possible to design a protocol where the music was sent multiple times, with the hope that if there are errors in the first copy of a block of audio, maybe the second or third copy will be intact. The flip side of that is more traffic on your WiFi for audio, leaving less for other purposes, but that's a tradeoff I would personally take. The protocol should decree a specific amount of buffering, so there is at least a chance that all devices will play in sync. (The simplest is to decree "no buffering"; everything is in sync but you don't get error correction.)

      Alternatively, one could make a WiFi gadget that uses TCP to stream files, queues up the files, and plays them in order. Then you will never hear the microwave; the worst case there is that the queue might run dry before you finish uploading another song to play. If you don't care about multicast, this seems a good strategy for an open-source WiFi music device.

      Personally, I just want one one network streaming device, hooked up to my home theatre receiver and driving my good speakers. So I don't care about multicast.

      With a suitable "client" app, it would be as easy to use as a music player: select your song, stream it to the player, and once enough of the song is buffered it could start playing. Then once the song is fully buffered, you could put away your phone/tablet/whatever and just listen to the music. Multiple clients could connect and upload music as long as there is room on the device to store the audio.

      The Raspberry Pi will be available with up to 256 MiB of RAM; with lossless audio it should be easy to overflow that. Just trying to queue up an entire album would likely do it. You could still use the Raspberry Pi as long as you use the SD card for buffering audio; with GB of data space you could buffer a lot of music.

      Much as I want to play with a Raspberry Pi, I'd rather use some other board that has more RAM, and not try to cache music on an SD card. A few GB of RAM would be plenty and even 1 GB would be adequate. Ideally the board should offer HDMI and we should use that to send the music to a nice home theatre receiver. Or S/PDIF I guess.

      P.S. I'm excited to read about the ODAC. Cool stuff. Thanks for what you are doing!

    6. Thanks Steveha for the added information. I was speaking from personal experience with actual WiFi audio devices. And if you go to the forums of those selling the devices, they're filled with WiFi related complaints and problems. While serious geeks may know how to optimize their WiFi networks, the average Joe often does not.

      Ideally network music players should work with most any WiFi access point/router and the music streamed from a simple file share, UPNP media server, or perhaps using DLNA (requires certification). That way someone can use a $200 NAS as their music source rather than needing to have a PC powered up and running all the time with special server software. This precludes running proprietary network protocols.

      There's also a trade off between buffering and usability. It may not seem like a big deal, but most people don't like "lag". They want to select a song or skip to the next track and have it happen almost immediately.

      Sonos developed their own WiFi and network protocol for their network music system. One reason they did so was to allow different players to reproduce the same content in sync avoiding an annoying time lag "echo" between different rooms. But even with their audio specific protocol their forum is still full of people complaining about WiFi issues and they've had to add extensive WiFi diagnostics to their firmware. It's their biggest support headache by a huge margin.

      So while I agree it's certainly possible to flawlessly stream lossless audio over WiFi, the forums are full of people who have been unable to make that happen. Short of lag inducing deep buffering, the ability to improve things only from the player side are fairly limited.

      I'm not sure where the best place to host it would be (diyAudio?) but if this discussion is going to continue it probably deserves its own thread somewhere.

    7. I was thinking more along the lines of an open-source new protocol. Those other protocols you listed are, as far as I know, UDP with no redundant data packets and no delay; designed for simplicity rather than robustness. That might even be the right tradeoff for most people.

      I don't know if anyone would be interested in a new, free specification for more robust lossless audio. I'm only saying that I don't think anyone has really tried, so far.

      Or possibly they tried it and customers hated it! As you say, people don't like lag. Since I haven't actually tried these ideas, it could be that the multiple-copies idea only works if you separate the blocks by so much time that the lag becomes a problem. If you have three redundant blocks in a row, and you turn on the microwave, maybe you lose all three.

      But it might be worth playing with. Maybe a college student is reading this and needs a research project?

  13. I'm really excited to see the finished product especially ODA combo with ODAC

    btw NwAvGuy what your opinion about Ibasso d7 it's only $180 and look good
    using XMOS and have class A amp?

    1. I haven't tested any iBasso products but a few iBasso owners have written to me about iBasso products they own. One caught iBasso flat lying in their output power specs. In my opinion iBasso appears to be a lot like HA-Info (see my comment above), Yulong, Audinst, Matrix, etc. All of these manufactures seem to be more interested in turning out nice looking products based around the latest FOTM trendy chips rather than proper engineering and measurements. None have publish any meaningful measurement data that I've seen. All have rather limited distribution from rather sketchy sources. If their products are so great why are they not being sold by larger more reputable dealers?

  14. I like where this is going. Shame about the closed-source condition on the ODAC... oh well. Maybe the design will be opened once the producer made enough money off it. By the way, are you interested in posting the final designs of the O2/ODA on some open hardware sites such as http://solderpad.com/? Just recently heard about such platforms.

  15. Pardon me if I'm asking a stupid question but what is your opinion on USB galvanic isolation? I understand the "benefits" but with your statements on power supply filtering such a isolator would do absolutely nothing for something like the ODAC right?

    1. That's actually a good question. Galvanic isolation is of limited usefulness for headphone listening because most headphone amps and headphones "float" with respect to ground. But it can be useful if you're planning to connect your USB DAC to another piece of gear that's grounded (such as a home A/V system, etc.). If you do encounter problems connecting a non-isolated USB DAC to another grounded piece of gear there are various ways to deal with that situation. It's also worth pointing out even the Benchmark DAC1 doesn't have galvanic isolation.

  16. Your writng is getting better all the time. This article left me with zero questions, which is obviously ideal.

    Thanks again for the update and all the hard work. I can't wait for the ODA's turn in the spotlight, though the O2 helps. :)

  17. Thanks to Robert above and everyone else for all the kind words. As for my writing it's still amazing how many errors surface after I publish my articles. It doesn't seem to matter how many times I proofread before publishing I always miss things. I've fixed at least a dozen or so errors since just last night. I need an editor ;)

    1. The age old concept of not being able to proof-read your own work never fails. No need to worry regarding editors as there are plenty of keen eyes watching this site more than happy to volunteer their services as seen on the comments of this blog entry (along with the rest of the internet wherever a comment section is actually available, case in point being the MPAA/RIAA 'propaganda' websites).

      That said; I appreciate the time you do spend in the writing of these blogs in a format for people (like myself) of a low level of Electrical Engineering knowledge and look forward to future posts about this product as you head towards RTM status :)

    2. "You might want to save a copy (highlight Ctrl-C) in case there are problems with your submission."

      May I make a suggestion to Firefox Users to install the Add-On called "Lazarus: Form Recovery" which has saved my bacon many times on a wide variety of websites (afaik it is still a free add-on; and FYI I have no association with the add-on besides being an end-user of it =) )

    3. You know, if you think about it, it's basically confirmation bias. You know what you meant to say, so your brain uses its impressive ability to fill in blanks on the fly to gloss over minor (even major) mistakes.

      One of my gradeschool English teachers was fascinated by it. She had passages written in gibberish that resembled English words. A reasonably experienced reader could "correctly" interpret the gibberish to English at most of their normal reading pace.

    4. A few years ago, I've seen something similar to what you mentioned: Each word in the passage has the first and last letter fixed, while all letters in between are jumbled up. It's still possible to read the passage at a slightly slower reading pace.

      But I digress.....

  18. Hi there NwAvGuy. This is my first time posting on your blog, though I've been following your adventures for several months. I'm really looking forward to the ODAC release. I strongly believe that when I buy the ODAC + O2 combo, it will be the last piece of audio hardware that I buy. I only have a beginner's understanding of electronics, but what I do understand is your mission with the ODA and ODAC, and I wanted to say thank you. Your work on these projects is making hi-fi more scientific and affordable at the same time, and I think we'll all be better off because of it. Well, the snake oil merchants won't be, but you get my point. :-)

    Best of luck, and thanks for all that you do (are doing).

  19. I was about to get an O2, buy I will wait to get the ODAC as well..
    Are you taking pre-orders now?
    Thank you very much!

  20. I'm not sure if it was mentioned, I read the article twice, but will the ODAC have 1 or 2 outputs? I'd like to connect this to my future ODA, but I'd also like to connect it to my receiver so my speakers can benefit from some future lovely ODAC audio.

  21. @Anon, the ODAC will "dock" inside the ODA which should have a preamp output to connect to your receiver. So you can use it for both headphones and your receiver/speakers.

    @Mario, Once things are finalized I'm not sure when orders will be accepted on the commercial side of things. I'll publish the details when I know more.

    1. will you limit the quantity available for purchase on the 1st batch?..i am afraid merchants will buy all stock and left people wanting 1 of each (oda odac) waiting for more production...

      anyway, i am already saving cash to get it whenever it becomes available :-) along with some new cans (probably dt-770 250, here in Europe they are pretty affordable)

      on a different note...how do you like the ncore amps? (hypex)

      thank you for the time and energy you are putting into this projects.

    2. To get the price down production batches will have to be fairly large. With automated SMT assembly it can take more time to set up all the machines then to run the job. So the price drops fairly dramatically as the quantity goes up.

      It's not up to me, but I think the plan is to talk with the obvious suspects who might want a large number of ODAC boards in advance and adjust the initial production quantity accordingly. But with a brand new design, everyone is probably going to be somewhat reluctant to make big financial commitments until the ODAC is more proven out in the real world.

      I like Hypex a lot. I've met Bruno Putzeys on a few occasions and have read his excellent articles. In my opinion he's a really smart guy and has contributed a lot to modestly priced high-end audio.

  22. Hi NwAvGuy,

    Another great effort. Thank you for your hard work and willingness to share.

    I'm a little puzzled about the secrecy surrounding the major IC's. The DACmini for example, uses a AD1896 ASRC running at 96kHz. Musical Fidelity's M1DAC-A has the TAS1020B for 96/24 USB feeding a SRC4392 ASRC running at 192kHz, which in turn feeds a DSD1796 DAC with JRC5532 opamps. Bel Canto's DAC3.5VB has no USB, but it has the same SRC4392 + PCM1792 DAC solution feeding OPA1632. Bricasti's M1 uses a AD1955 with external FPGA filter, AD843 I/V and discrete buffers. It has no USB. HRT's entire lineup has the same TAS1020B for USB.

    So I guess I'm trying to say it doesn't hurt to say what the major IC's are. After all, the secret sauce is really in the implementation as your above blog clearly attest to. Alright, I'll admit it - I'm really curious. Haha.

    Arius from Diyaudio.

    1. We're just trying to avoid, where possible, giving other potential commercial interests a head start. Anything that lowers the financial risk at this point has some merit. The cat will be out of the bag soon enough if the project stays on schedule for April production.

    2. This doesn't really make sense... I thought your blog and designs are not for profit... What kind of financial risk can there be for someone who is not making money from the design?

    3. Please read the FAQ question regarding publishing schematics and a parts list. The ODAC cannot be built by individuals. They would have to buy 500+ expensive ICs under a contractual agreement stating, among other things, they will not resell them. So the only viable option is to have the ODAC be commercially assembled.

      Further down in the FAQ I explain I'm not involved with the financial or commercial side of this but someone has to be. The risk is to them, not me.

      I started off hoping to design an open source reasonably priced 24 bit USB DAC that works without proprietary drivers in Windows. It turns out that's not possible without signing contractual agreements with chip makers to even get your hands on sample quantities. Hopefully there will be more IC options in the future, but for now, that's just the reality.

      So even assuming I could somehow otherwise get the sample chips, if I were to just release the design into the public domain it's unlikely anyone would want to take the considerable risk to build it not knowing if multiple others were in the process of doing the same thing. It's a lot to ask for someone to risk buying parts for 500+ unproven DACs not knowing what sort of competition they'll face once they get them built. I could have put up the money but then I give up my entirely non-commercial position.

  23. Hello NwAvGuy,

    I just read trough your post, after following your previous work and efforts to give your work to the diy community. I really appreciate what you do and I wish you all good health for all this hard jobs of yours.

  24. Hello NwAvGuy,

    considering your interesting article about opamp myths and facts, I have been thinking how much of that can be said about DACs as well. The industry wants me to believe, that my opamps sound bad so that I buy more expensive opamps or hardware which features those. After what I've read here, I would be lucky if the end result of that wasn't audibly worse. But what if the same goes for DACs? I simply don't know if my DAC is bad or not. How am I to determine that?

    The only criteria I have are again names and specs, like Wolfson and 24/192 etc. But then again this could be the same kind of misdirection as with the opamps.

    Perhaps you could write a similar article about DACs as well.

    1. You're correct that just knowing what chips are used and perhaps having a few vague specs from a manufacture doesn't really tell you if you have transparent DAC or not. Even the finest parts won't work well if they're not properly implemented.

      If you buy from a major reputable audio manufacture with a focus on solid engineering, like say Emotiva, Cambridge Audio, Centrance, Benchmark Media, or Grace Designs, the odds are good you'll get a well engineered product. If you buy from a company that caters to audiophile myths, like say NuForce, Schiit Audio, or even Musical Fidelity, the odds of getting a solid product are more risky. And if you buy from a company that sells most of their product on eBay or through some sketchy website, like say HA-Info or Audio-GD, all bets are off.

      I'm still thinking about a future technical article on DACs. There are a lot of myths I would like to explore but it gets to be a very complex topic. There are myths regarding sampling rates, bit depths, software volume controls, USB vs S/PDIF vs AES, asynchronous USB, up-sampling, USB-to-S/PDIF converters, optical vs coaxial, jitter, digital filtering, analog filtering, ripple, NOS (New Old Stock) chips, "balanced DACs", DAC power supplies, ASRC, 32 bit DACs, etc. Taken as a whole it's a far more complex topic than op amps.

      In the meantime, your best bet is to stick with products that have been independently properly measured. Or, at the least, those with reasonably complete specs and some evidence the manufacture actually performed proper testing and isn't just applying creative marketing or copying numbers from the DAC chip datasheet.

    2. I primarily wonder if onboard sound on personal computers and notebooks is as bad as people say. I think it's true when it comes to multi balanced armature in ear monitors and 600ohms headphones, because of a too high output impedance or not enough power. But for one that's only the amplifyer part and second it applies only to specific headphones. Let's say you have good headphones which are easy to drive, like the Sennheiser HD 558 for example.

      Will there still be an issue with onboard sound? It can't be volume, because the HD 558 go more than loud enough with any laptop or netbook I have tested.

      With reference to onboard sound as a layman you are really lost, because the manufacturers are very reserved and don't give you a lot of info about the gear they're using. It's just terms like "conexant" or "realtek" "hd audio".

    3. There often are audible problems with built-in audio. Many computers have audible noise, bass roll off due to cheap capacitor coupled outputs, high output impedance, insufficient power, high distortion, and/or bargain basement sound chips with poor performing DACs. I have a relatively expensive HP TouchSmart All-in-one PC with literally terrible built in audio no matter what headphones I use. It suffers from several of the problems I just listed. The Apple Macbook Air I recently reviewed is much better but still has a few significant weaknesses.

      And once you get to a headphone like the HD600/650 or AKG K/Q701, there are almost no PCs that can properly drive them. Adding an amp can get you enough power but you may still be stuck with some of the other problems I listed above unless you use an external DAC.

    4. I see the brands you listed, and how you grouped them into different categories, but I just want a list. Could you please group the different manufacturers into a list, with different categories for "solid engineering", and another for "flashy parts with so-so engineering", and a final one for "probably shoddy engineering"? (or whatever categories you like)

      A list like this would really help. Thanks, I appreciate it. :-)

    5. Thank you very much for the helpful replies so far.

      Yet I am still pondering on how to judge a dedicated soundcard, if the amp section is not an issue because there is a also dedicated amplifier in play.

      Dedicated soundcards have in common with onboard sound, that they will not drive multi-ba in ear monitors and top notch headphones properly. For the latter you could buy an Asus Xonar Essence, however this probably would not solve the high output impedance issue that screws up the IEMs frequency response. So amplifier wise, a dedicated amplifier is the way to go.

      Then again some of us already own a rather sophisticated soundcard, that might not be up to amplifier task, yet features a potentially respectable DAC. So those of us are wondering if we should keep these soundcards and just invest in a proper amplifier.

      There are some soundcards which come to my mind, like the Creative X-Fi's (Cirrus Logic CS4382) or Asus Xonar DX (CS5361). They are reasonably priced and seem to have a decent DAC.

      Are those up to the task regarding the DAC part

    6. @Anon, you're probably hearing more bass from your laptop because it has a high output impedance. That results in a bass peak at the resonance frequency of your headphones (which is likely around 100hz) and generally less controlled and accurate bass. You might prefer the added bass from the higher output impedance.

      @Xactacx, while I can express general opinions, and my reasons why, it's going a bit far to try and categorize gear into black and white categories without testing each one. Instead, I try to help more people know what to look for, what's more important if you're interested in accurate sound, etc.

      @Simon, you're correct about Asus having too high of an output impedance for many headphones even with their flagship products. It's hard to say if you would gain any benefit from an external DAC if you're already using a decent amp. One problem with internal soundcards is they're much more at the mercy of the PC they're in. They can be acceptably quiet in one PC and have audible noise in another. So even if I were to test soundcards others might get very different results than I did. That's one reason I don't test them.

    7. @Simon: the Sennheiser HD558/HD598 have one of the largest impedance peaks of full size headphones, so these are actually quite sensitive to the output impedance of the device driving them. Different damping factors can easily make audible differences with these headphones.

    8. Even though the noise level of a sound card may very depending on the machine it is being used in, it is still worth testing them for other parameters. Although noise could also be tested in a "quiet" and a "noisy" PC to get a general idea, as well as to see how much the card is sensitive to the interference. I guess the main problem is that there is simply not enough time to test so many devices.

      There is very little usable information available on the performance of sound cards, other than the results of - often not very competently performed - unloaded RMAA tests. Basic parameters like the maximum output voltage and the output impedance are almost never known, so questions like "will card X drive headphone Y well" cannot be answered.

      When not degraded too much by interference or other problems, a sound card can actually perform quite well for the price, at least as far as the DAC is concerned; the SNR is often above 110 dB in loopback tests even for some relatively cheap cards. The main weak point is usually the headphone jack, which often has high output impedance, limited maximum voltage or current, or small coupling capacitors.

    9. John Atkinson at Stereophile did test two of the Asus Xonar flagship cards. They both use the somewhat flawed TI TPA6120 headphone amp, have a relatively high output impedance, and suffered from some other odd behavior (especially related to the proprietary drivers and configuration options).

      As I've said many times, I'm not a big fan of soundcards for anything but gaming for the following reasons:

      1 - The noise issue mentioned above. The inside of a PC is about the worst place imaginable for a high-end audio device.

      2 - They're leftover dinosaurs. Before the USB audio standard was born, some 15 years ago, soundcards had a reason for being. Since then it's much harder to argue they do. Fewer and fewer PCs even have suitable expansion slots for them. Anyone but hardcore gamers are increasingly buying smaller PC's including laptops, netbooks, ultrabooks, tablets, all-in-one PCs, small HTPCs, small form factor desktop PCs, etc. Only old school "tower" systems tend to have free slots for soundcards.

      3 - They generally require proprietary drivers that are often unstable and/or create other problems.

      4 - They offer few or no advantages over USB sound hardware. Internal sound cards are generally not less expensive or better performing than USB sound hardware. If anything the reverse tends to be true.

  25. Hey NwAvGuy! I've been following your blog for a bit now, and I'm really impressed. I love seeing the more technical side of things.

    Three quick questions:

    Will there be a preassembled ODAC/ODA made?

    How does the ODAC respond to noise inside the computer? (For example, with my FiiO E10, whenever my WiFi was on (on my MBP) and I browsed the web, I could hear clicks and interference through my headphones. This was even more evident on page loads. I'm pretty sure this is electrical noise coming from the WiFi card inside the computer.)

    And lastly, do you know how it would compare to a Wavelength Proton? (Easily the best sounding dac i've heard, under 2k)

    Thanks! Love your blog, keep it up!

    1. Yes JDS Labs, and others, have already expressed interest in offering a fully assembled ODA + ODAC. It's also possible they may sell the O2 + ODAC combo and perhaps even a standalone ODAC.

      WiFi creates RFI (Radio Frequency Interference) and most audio devices have some susceptibility to it. I'll be testing the ODA + ODAC and O2 + ODA for RFI immunity. The O2 and ODA have RFI filtering on their inputs. Using a USB cable with a ferrite "choke" located near the DAC end of the cable will often solve (or at least greatly improve) RFI problems. That might help with your FiiO E10.

      I've never measured or listened to any of the Wavelength DACs. Given their love of things like vacuum tubes and Black Gate capacitors, they appear to be more into audiophile snake oil than proper engineering. That said, if the Proton measures reasonably well, I'd love to arrange for a public blind comparison with the ODAC + ODA.

    2. Can't wait to get ahold of the ODAC/ODA to rid myself of the E10, and do some justice to my hd 600's!

      Very interesting point you bring up, I'd love to see how the Proton measures, with your thorough testing.

  26. Slotting the ODAC into the space in the O2 occupied by the batteries gives a very neat solution, but I wonder if it would be possible to keep the batteries for a portable DAC/Amp combination?

    If a USB socket-sized slot was milled in the edge of the O2 PCB underneath the batteries (where there are no circuit traces) there looks to be enough space to fit the ODAC under the O2 board rather than on top, without the underside of the ODAC fouling the case. Not very elegant, but it shouldn't be too difficult to find a way to fix the ODAC board to the O2 board in this position.

  27. I cant wait to have this magical pair!! ODAC+O2.
    As an engineer.. Im kinda tired of these "audiophile" designs drafted by ears..

  28. I'm curious about how much the ODA is projected to cost in a pre-built form from one of the manufacturers that picked up the O2? Are we looking in the $150 ballpark, or will it be more because of the combined increase in technology packed into one unit?

    1. The assembled price is up to others and it's too early to ask. There are three hurdles. First the final pricing on the parts and assembly costs for the raw board has to be determined, then the assembled board can be priced both for single board DIY sales and in larger volumes to those who want to sell finished DACs/ODAs like JDS Labs. Once those amounts are established, they can price their finished versions accordingly. It will depend on the enclosures and panels used, etc.

  29. I've learned so many things from this blog alone that head-fi couldn't teach me. Pretty much all of my questions were answered but I'm really curious about one thing. I ran some searches and I couldn't really find anything related to it at all.

    What is your opinion on people replacing their cups to improve the sound of their headphones? For instance, I have the D7000 which has many mods that are supposed to "enhance" the sound quality. While I can probably figure for myself that the dynamat mods and the custom ear pads will change the sound (for the better or worse), I'm not sure if the wooden cups will make a difference in sound at all. However, I do admit they look beautiful.

    Sorry that this is totally unrelated to the ODA/ODAC. Feel free to ignore this comment if you are too busy to respond :D

    PS: I really love your blog. I thought I was getting decent performance with my essence STX until I used an amp with a lower output impedence. Now, the headphones sound much more neutral.

    1. Thanks for the encouragement. While I have a fair amount of speaker design experience I can't say I've done any headphone earcup mods. I can say it's human nature to associate materials with sound quality in some intuitive but invalid ways. It's just the way our brains work. If you replace film capacitors with ceramic capacitors it's easy to think an amp sounds more "brittle" or "hard" because ceramic is a harder material. People think thin cables result in constricted and thin sound. Etc.

      The same sort of bias can easily extend to using wood for things like earcups. Warm rich looking woods bias people to hear warmer and richer sound--especially compared to plastic. Wood is generally perceived as a higher quality material than plastic.

      The best sounding wood for speaker enclosures is MDF which is basically particle board. But particle board is rather ugly and is otherwise associated with cheap furniture and $29 flimsy bookcases from Ikea. Exotic expensive hardwoods may look much better but usually are nowhere near as "dead" and inert as MDF. So speakers typically use wood veneer over MDF.

      There's nothing very special about the acoustic properties of hardwood. The right composite plastics, especially with a lossy viscoelastic layer (like Dynamat), are likely to be more neutral.

      You also have to consider cost and weight. Some wood headphone I've tried are downright "clunky" and not very comfortable. And the cost for such "upgrades" is probably much better spent elsewhere.

      When you get to the level of the D7000 I'm guessing Denon didn't cut a lot of corners in their construction. It's not like you're trying to improve a $69 pair of Grados.

      I'm fond of car analogies. To me, modifying the D7000 is a lot like buying a new Porsche 911 and giving it the same Pimp My Ride treatment you see on 15 year old Honda Civics. It's also a slap in the face to the Porsche engineers who created a great sports car. If oversize wheels and a huge wing really made the car handle better, they would have offered them from the factory.

    2. Not that it's the same, but grados/magnums change drastically with the cup material and the cup length and any coating on the inside of the cup.

      I would think that it could very well effect the demons, but perhaps to a lesser extent. The best way to find out is to diy.

    3. The D2000/5000/7000 are all really similar. There are some tweaks to the driver and fancier looking cups but from what I can gather they have the same corners cut in regards to weight vs resonances. For improving the sound, constrained layer damping like dynamat or something is more important than changing the hardwood that the cups are made out of.

      If you're going for some sort of colored or "romantic" sound like some of the AT woodies then the choice of wood can be important but if you're just going to slap dynamat on the inside of the cups afterwords then the choice of wood becomes mostly aesthetic.


    This reminds me of a story about the layout of the logic boards for the original Macintosh.

    I can understand perfectly the desire for an aestheically pleasing layout, it can be subjectectively satisfying to know that the parts that can't be seen have also been considered from an aesthetic point of view. That being said of course, design is not what something looks like; Steve Jobs even said as much many years which is why that story amuses me. If the quest for the aestehetic ultimately compromises the objective performance of the device then it should give way to more functional considerations. It's great to see that this is the case with the ODAC.

    How something looks can be play a huge subjective role in a person choosing product A over product B and that's fine so long as they are honest about their subjective bias. Saying something is better because they persoanlly prefer it's appearance (or other subjective attribute) is somewhat disengenious, as is stating without qualification that a given technology is better. One sees such statements in software development as well, where x or y framework or language must be better because it was used by so and so company. Ultimately implmentation is more important than the current flavour of the month fanboy favourite.

    1. I had heard the classic "Steve Jobs wanted the board to look nicer" story and it wouldn't surprise me if it's true. They had to revert back to the more visually "ugly" PCB layout because the Jobs way didn't work.

      There's a big difference, however, between digital and analog hardware design. Digital designs tend to either work or not. When they don't work correctly, even if it's a rare problem, the result tends to be obvious. But in something like an analog headphone amp or the analog side of a DAC, problems are often subtle and difficult (or sometimes impossible) to reliably detect by ear. That's the main reason why so many half baked amp and DAC designs gain some acceptance despite their flaws.

    2. I'm very glad that we not only have someone sweating the details, but also explaining why those decisions have been made and what their impact is. I for one cannot wait to place my order for one. I'm currently vacillating between waiting for for the ODA and ordering an O2, Epiphany Acoustics here in the UK are predicting a 6-8 week for an O2 so I may just hang on for the ODA/ODAC combination.

  31. As a question concerning bit-perfect output, my understanding is that Windows default behaviour is to resample everything to a common bitrate for output unless you're using something like WASAPI? is there a way to get bit-perfect output through a USB dac (or soundcard, etc.) without resorting to WASAPI, i.e. for something like VLC

    1. You can normally get bit perfect output from Windows 7 automatically. You can also, in the Sound control panel, set the default bit depth and sample rate preference for each audio device in the system. So the ODAC, for example, can be set to 24/44 if you mostly play CD audio.

      The dScope is capable of verifying bit perfect output and I can attest you can get it without using WASAPI. XP is a bit more cranky than Win7 but you can also get bit accurate output from XP without WASAPI.

      It's also important to note that going from 16 to 24 bit, or the reverse, isn't re-sampling and will not add artifacts to the audio (although if you truncate from 24 to 16 bits you may lose some information).

      In the right hand column of this blog there are a couple links to more information about computer audio in general.

  32. The ODA/ODAC combo clearly need its own name.
    Maybe ODADAC?

    1. We engineering geeks are generally bad at things like product names. I'd be happy with "ODA + ODAC" on the front panel but that's not very sexy. I'm open to better suggestions. ODAMP almost sounds like an Ikea product.

    2. Objective 9000 Elite PRO Signature Edition. Haha, just kidding.
      Maybe, Objective Duet, or something like that?

    3. I kinda like Objective Duet

    4. Objective^3? May not be original, but it does the job!

    5. How about:


    6. I like the O3 idea. You could call the O2 + ODAC the O2.5. You could poke some fun at your detractors with the name:

      O3: No Schiit Desktop Edition
      O3: Hey Jude!
      O3: ABX much?
      O3: And the banned played on

    7. O2 = Oxygen
      O3 = Ozone

      I think air is transparent and it really reflects the O2 & ODAC perfectly.

    8. I'll put my vote in for


      A nice logical naming scheme that keeps things consistent across the different possible combinations in the product line.

  33. Excellent work NwAvGuy! I keep checking your blog regularly for updates and this one was a nice surprise after a while.
    I am going to build an O2 in a couple of days with the JDSLabs PCB. If all goes well, I'll be waiting for ODAC to get released.

  34. What drivers are going to be used?
    Are they going to be made by you or someone else?
    Then they will be open source which is nice.

    My only issue with the standard windows driver is that it bypasses the volume control, then also the mute button. While normally not an issue, when using the DAC for an HTPC, the mute button directly on the PC is more convenient when needing to quickly mute the entire system.

    1. In both Windows 7 and XP (I haven't yet tried Vista) the ODAC works beautifully with the default Windows drivers. Both the operating system volume control and mute feature work. I've also verified it works in OS X Lion, Snow Leopard, and a couple of Linux distros.

      One of the main benefits of a 24 bit DAC, like the ODAC, is allowing use of software volume controls without audible penalty from loss of bit depth at lower volumes.

  35. Dear NwAvGuy, you may be interested in this article talking about 24/192 audio.



    1. Thanks for the link. I agree with 95+% of what the author of the article has written. He writes better than I do and we share similar views on several topics. I agree with his concern over the direction Apple seems to be headed with music formats. He references some of the same articles I have--such as the AES Meyer & Moran study.

      I do want to clarify a couple of things that might otherwise lead to some confusion:

      There's a significant difference between playback audio formats (i.e. 16/44, 24/96, etc. files) and hardware capabilities (i.e. 16/44 DACs and 24/96 DACs). The article is mostly talking only about recording/playback formats--not hardware.

      I agree 24 bit music is of limited benefit as a playback format--especially 24/192 music. But 24 bit hardware does have value. The author doesn't really address the issue of 16 vs 24 bit DACs and software volume controls. With a 16 bit DAC, and the volume set to -36 dB, the DAC is only receiving 10 bits of data. If the downstream volume is high enough, it's entirely possible to hear the noise floor of a 16 bit DAC--especially with headphones.

      Audio hardware that supports 24/48 and 24/96 as well as 24/44 helps avoid operating system re-sampling when high resolution music is played. Some audiophile music downloads are only available in lossless form in high resolution formats. Having a DAC that supports the native format may result in better sound as it avoids re-sampling.

      The author also talks about how 16 bit audio can exceed the theoretical 96 dB of dynamic range, and while he's correct in what he says, he's painting a somewhat unrealistic picture. The accepted way to measure dynamic range is to measure the total energy of the noise floor within the audio band--what we can hear. The audio analyzer sums all the noise from 20 hz to 20 Khz. Measured in that way, 16 bit DACs typically deliver around 96 dB of real world dynamic range. With proper dither it is possible for a human to pick out something like a single tone that's lower than -96 dB but the overall noise is louder than the tone which is hardly a desirable situation.

      Here's the link in clickable form: 24/192 Music Downloads

    2. Dear NwAvGuy, thanks for your insightful comments.

      An interesting discussion followed in Slashdot, IMHO it puts some uses of 24/192 into perspective.


      Thanks for your blog!

  36. There are two things which are not completely clear to me.
    "There’s a provision on the board for a 3.5mm stereo output jack..."
    May I suggest adding RCA jacks by default to the standalone ODAC? I think it's better for cable management, the average audio listener has a pair of RCA's as interconnects and either you use a stereo 3.5 jack -> dual RCA adapter which applies pressure on the plug, or you have to make a cable for that. Personally, I don't like the cable version because I it's hard to find a 3.5 jack that would fit to my usual interconnect cable.
    "DIYers can also panel mount 3.5mm or RCA output jacks..."
    By panel mount you mean the panel will be ready to accept RCA connectors?
    And if I buy a standalone ODAC when it's available (preferrably with RCA's :)) and I use it in my current rig, will I be able to attach it in an ODA? Or is it a little different in design, outputs etc.
    Keep up your good work and thank you!

    1. There's not enough room for side-by-side RCA jacks on the board with the required spacing (audiophile cables often have rather "thick" RCA plugs) and still have it fit in the O2 otherwise I agree RCA jacks (or ideally both) would be better.

      What I meant by "panel mount" was chassis mounted off-board jacks such as the RCA input jacks many have added to desktop versions of the O2.

      Also, if you stay with only the 3.5mm jack, there are lots of high quality 3.5mm to RCA stereo cables available so you don't need to use an adapter.

    2. Thank you for your answer!
      I guess I will stick to airwiring.
      And about my second question, the standalone ODAC will be the same as the "raw" panel -with a jack output of course- so I can put it into an ODA later, right?

    3. It's the same PCB for the O2, ODA or standalone ODAC. The only choice is if you want to install the 3.5mm output jack. You could start with the ODAC in the O2 or standalone and later move it to the ODA if you want.

  37. Let the hype train begin!!! Already got the fantastic O2. I'm guessing you're gonna trademark / IP protect this to prevent reverse engineering? Can't wait for the ODAC release!

  38. I have a relatively efficient pair of headphones that will be right in my comfort zone for listening with 40dB of attenuation from a 2V signal (mid 70's). So in my mind, unity gain is still too much. So even though I don't need a headphone amp, I'd like to have all the other side benefits of your designs. So my question is this: will the ODA have a slick way of incorporating a voltage divider on one of the gain settings? If not, will I have a way of easily dropping the ODAC's output voltage? If not, is there a volume control modification that would solve the problem?

    I think I'm not alone in wanting the pure sound but not needing amplification.

    1. No you're not alone and yes I plan to accommodate those needing less than 1X (unity) gain.

  39. I'm still enjoying my O2 (JDS Labs) and I've been following your progress on the ODAC with great interest. I was disappointed to learn it will be USB only. I understand your reasoning and can't say I disagree, but I personally don't plug into my computer to listen to music. I stream over Wi-Fi to a Logitech Squeezebox Touch, so S/PDIF is important to me. I'm shopping for a DAC with coax and/or optical inputs, but I'm finding it a lot harder to see through the snake oil with DACs.

    Have you have tested or listened to any of the DAC's from the companies you respect and can recommend any DAC's that have S/PDIF and/or optical inputs?

    You've mentioned Emotiva several times and I've been following them for over 2 years now (I was on their waiting list for the UMC-1 once upon a time). Do you know anything about their (discontinued?) XDA-1 beyond what their website says? It seems to good to be true for $250.

    What about Music Hall, Channel Island Audio, and Simaudio (sold by MusicDirect.com)? They offer standalone DAC's that retail for less than $600.

    As always, I appreciate any thoughts or insights you might be able to offer.

    1. I generally have a lot of respect for Emotiva gear although I haven't tested the XDA-1. The biggest issue with the XDA-1 is it's only 16 bit over USB. If you always leave the volume all the way up on your PC and control the volume at the XDA-1 that's not a problem. I suspect they're working on a 24 bit version but it will probably be $300 - $400.

      I don't have a lot of respect for Music Hall considering the prices they charge. Their gear I've seen uses cheapo capacitor coupled headphone outputs. I don't know anything about Channel Island. Simaudio seems a bit sketchy to me. MusicDirect has a whole catalog full of various flavors of snake oil.

      Does the new Musical Fidelity V-DAC Mk II have S/PDIF? If so that might be worth a look although I haven't tested it. A safer, but expensive bet, would be the Centrance DACmini with the 1 ohm output upgrade. Stereophile recently reviewed and measured it and it's a very solid DAC and headphone amp.

    2. I've been wanting to know the answer to this exact question. My assessment of the market concurs with this, but I don't know the manufacturers like NwAvGuy does.

      I've considered Music Fidelity V-DAC II since the original did pretty well according to Stereophile, but at the same time that company sells a power brick for the same price, so I'm skeptical.

      There's the DACMagic 100 that's coming out. Haven't seen any reviews on it yet, but it's the old DACMagic without headphone out and some features like digital filters

    3. Were you both (@palmfish, @nwavguy) aware that the Touch community have been investigating driving external DAC's off the Touch's USB port.

      See the following threads for details

      If their efforts come to fruition, a Touch / ODAC / ODA would make a great Headphone based listening solution.

      I'd also be interested in what real world benefits this would provide over running an ODA using the Touch analog outputs as input for the ODA.

      Stereophile measured the Touch

      Any comments?

    4. I think the new Audioengine D1 would be worth a look. SPDIF and USB input.

      Their wireless D2 solution appears to measure and sound very good:

      I'm not certain if the v9lume control wokrs on both the headphone output and the RCA line-outs. 10 ohm output impedance on the phones.

    5. I did read some buzz about "hacking" the Squeezebox Touch for USB output. Maybe I'm still in the dark ages, but it's my opinion that even with the recent advances in USB music systems, S/PDIF is still superior. I also wonder if the modification does work out, will be 24 bit capable.

      I know it isn't a blind test, but I can very definitely hear the difference between the Squeezbox Touch RCA analog output and the output from my current separate DAC (line out from my Sabre ESS based Peachtree Audio Nova). I have also compared the RCA output of my Squeezebox with my Redbook CD player analog output. To my ears, the Nova and CD player both sound the same and the Squeezebox is definitely inferior. Admitting that the comparison isn't scientifically or statistically valid, I do believe that I hear some shrillness and thinness directly out of the Squeezebox Touch. Personally, I am convinced that the Touch will benefit from a standalone DAC.

      After posting my question above, I ended up doing a lot of surfing last night educating myself and pricing various "affordable" DACs available right now. Based on my positive experience with Peachtree, I think their DAC*iT is probably a good unit. I also think the V-DAC II looks (sounds) good - especially for the price (although I recall NwAvGuy previously cautioning someone about Musical Fidelity. However, the company and DAC that keeps coming up to the top of my list in this price range is the Cambridge Audio DacMagic (and the new DacMagic 100.

      The DacMagic is a previous generation unit that got many favorable reviews (including a very favorable review and measurements by Stereophile). Stereophile even made comments comparing the DacMagic to the V-DAC, which I think lends credibility to both. For my needs though, the DacMagic might be overkill because I don't need balanced outputs and the switchable filter might confuse things for me (which filter is the "neutral" one?).

      Cambridge Audio also just introduced the DacMagic 100, which has a newer chipset and presumably has improved upon the older unit. I like that it is smaller and simpler (no balanced outputs or switchable filter), and it uses a newer Wolfson WM8742 vs the dual WM8740's of the older DacMagic. One advantage that comes up repeatedly is that the newer unit has superior USB performance, which although of no use to me, is still promising.

      One thing that I don't remember being mentioned here previously is the benefit (or lack thereof) of having dual chips (one per channel) vs. a single chip. I'm guessing that NwAvGuy will suggest that, all else being equal, it is irrelevant.

    6. @Palmfish, I'm really not trying to be obnoxious but "I know it isn't a blind test, but I can very definitely hear the difference" is classic. Until you do a blind test you really DON'T know you can definitely hear a difference. That's been proven over and over. I reference an AES study in my May Subjective vs Objective article where 70-some percent of people heard a "clear difference" where none existed.

      Given how well the Touch has measured (by Stereophile) if you really can hear a difference in a blind test it's likely your external DAC is flawed. USB, for computer/network audio has a number of advantages over S/PDIF. You might want to read my CD's ARE SO 1980's article from July.

      The new V-DAC and DacMagic, as you suspect, may be fine DACs. Until someone properly measures them, however, we can only guess. And yes, dual DAC chips is just a marketing thing in terms of meaningful benefits.

    7. No worries, I expected you to say that (hence the disclaimer). I have read your Subjective vs. Objective article and I agree with you completely. Unfortunately I don't have the resources or facilities to DBT 20 different DACs. I'm a firm believer in blind testing too and I realize that I am as susceptible as anyone to hearing what I want/expect to hear, but I also think that it is possible to be objective if the differences are large enough. I've read your blog and I've read Floyd Toole's book and I'm a believer. On the other hand, the "How to Listen" software download on Sean Olive's blog demonstrates that if the difference is large enough, you can hear and identify differences consistently.

      But this kind of leads into the underlying issue (which you have addressed). Until the industry embraces standardized testing (like the automobile industry), there is no way to be assured of what you're getting. Since we don't have the ability to test multiple DACs in our own listening room in controlled conditions (DBT), then all we are left with is subjective "professional" reviews, lab measurements from trusted sources, trust in the principles of respected companies/individuals, and lastly, our own ears.

      After more reading today, I discovered that Stereophile has tested and measured the DacMagic, the original V-DAC, the Squeezebox Touch, and several Peachtree DACs.


      I'm not an engineer so I can't say I understand all of the measurements, but they appear to be some of the same tests you perform. Both the Peachtree and the Cambridge Audio DACs subjectively tested and objectively measured very well, as did the V-DAC and the Squeezebox Touch. So with DACs, if the meaurements are good and the company stands on sound engineering principles, all you have left is how it sounds to you - however flawed that may be.

      I just purchased a DacMagic an hour ago so I'll get to do more listening soon. I've done all anyone can do - educated myself more than the average bear and exercised due diligence in my research of objective and subjective tests. Until testing methodology is standardized and DB testing becomes de rigueur in the industry, that's all anyone can do. I may not be able to trust myself to reliably/accurately hear differences between the DacMagic and my other units, but if the DacMagic is indistinguishable and/or does no harm in my opinion, then I guess that's the best I can do.

    8. For a 16 bit DAC the old DacMagic was a solid DAC. I suspect the new one is probably even better. It's enough of a mainstream (and sufficiently expensive) product someone will probably measure one fairly soon.

    9. The old DacMagic is 24 bit (Wolfson WM8740).

      Have you looked at the Stereophile measurements for the DacMagic (link in my post above)? I'm curious to know if their measurements are thorough and what you think. I'm not an engineer and don't know what a lot of the technical measurements mean, but I trust your knowledge.

      Also, if you are willing, I would love to get your thoughts on the measurements on my other DAC I currently own...


      On the Peachtree, John Atkinson mentioned an output impedance anomaly I'm also curious about. I have the Nova, not the iDecco, but the only difference is the Nova has a slightly more powerful amp - everything else should be the same.

      I've recruited my daughter to assist me in blind testing my three DAC's once I have them all on hand. I have a lot of combinations to listen to (the Squeezebox analog out, the Squeezebox S/PDIF and optical through my Peachtree DAC, and the Squeezebox S/PDIF and optical through the DacMagic). I can also hook up my laptop via USB and and include that through the Peachtree and DacMagic.

      The Peachtree Nova has all of these inputs built in so switching between sources should be fast and simple. I will make sure volume is matched as close as I can (by ear and with my Radio Shack SPL meter). It may not be scientific, but it is more controlled and I think it will be fun.

      Just out of curiosity, you've mentioned benchmarking/comparing your O2 and ODAC to the DAC1. Is all of your listening done blind or do you also use subjective listening - maybe in the earlier stages to see if you're close?

      Thanks again for all your contributions NwAvGuy. I've been involved in this hobby for over 30 years and I've learned more in the past 6 months than the entire rest of my time thanks to you and a few others out there.

    10. @palmfish: A big problem with subjective tests (even blind tests) is that they just identify differences and/or preferences, not accuracy.

      Using a simplistic example, if speaker and room acoustics result in an exaggerated high end, the listener may prefer the sound of a tube amp that droops down a few db between 10kHz and 20kHz. Then when they audition speakers, they might go for others with the same sonic flaw as that would sound best with their rolled-off preamp output.

      That kind of subconscious tuning took place for years with LPs, as users made speaker and equipment choices to tame the low frequency acoustic feedback that was so common with even higher-end turntables. Then CDs came out and those listeners proclaimed them to be inferior, sterile, or lacking "warmth." In many cases, it was just that the linearity of the CD source was not working well with their LP-tuned, bass-attenuated "audiophile" systems.

      I think that there has been inadequate study to correlate measurements with hearing. Part of the blame for that falls on the subjectivists who won't participate in the double-blind tests. Researhers need to know that they are correlating measurements to perception rather than imagination. Another area where I think that more study is needed is in designing measurements to test how outputs interact with reactive (inductive and capacitive) loads. As NwAvGuy points out, output impedence is a large part of that, but at least one paper has shown that headphone amps with similarly low output impedences still sometimes show marked differences in frequency response when driving reactive loads.

    11. Someone correct me if I'm wrong, but it's my understanding the original DacMagic is only 24 bit via S/PDIF. I'm fairly sure it's a 16/44 or 16/48 DAC via USB as that was fairly normal way back when it was designed.

      While I get Peachtree is trying to fill (or perhaps even in some ways create) an audio niche, I have concerns about their approach. For one thing, as I've hopefully made clear elsewhere, output impedance is critically important for many headphones. It's not a good sign if Peachtree got it wrong. And vacuum tubes, for anyone interested in accuracy, are a marketing gimmick, degrade performance, and a waste of money. They amount to either added distortion or snake oil.

      Blind listening is a fair amount of work, so no, I don't do all my listening blind. It's especially tricky to compare two USB DACs as you can't normally send the same bitstream to two devices at once. But, unless something is grossly flawed, blind listening is essential before you can draw any conclusions about sound quality differences.

    12. @Palmfish

      As shown on the Cambridge Audio DacMagic Website:

      DacMagic Digital to Analogue converter

      D/A Converters: Dual Wolfson WM8740 24bit DACs
      Digital filter: Texas Instruments TMS 320VC5501 DSP upsampling to 24bit 192kHz
      Analogue filter: 2-Pole Dual Differential Bessel Double Virtual Earth Balanced
      Frequency Response: 20Hz to 20kHz (±0.1dB) - steep filter disabled
      THD @ 1Khz 0dBFs: <0,001% (24 bit)
      THD @ 1kHz -10dBFs: <0.001%
      THD @ 20kHz 0dBFs: <0.002%
      Signal to Noise Ratio: -112dBr
      Total correlated jitter: <130pS
      Crosstalk @ 1kHz: < -100dB
      Crosstalk @ 20kHz: < -90dB
      Output Impedance: <50ohms
      Output level (unbalanced): 2.1V rms
      Output level (balanced): 4.2V rms (2.1V per phase)
      ***Digital input word widths supported: 16-24bit (16 bit for USB)***

  40. @Anon, while not cheap, the new DACmagic should be a solid piece of gear.

    @Anon, post 2005 Squeezebox gear designed by the original Slim Devices team tends to be respectable from an engineering perspective. I think the Touch came after Sean Adams left (post Logitech acquisition) but his solid engineering work was probably retained from earlier players. For those not familiar with it, Sean designed the $1500 Transporter which set new standards when it came out. Its performance rivals $5000 CD players.

    I don't see anything to worry about in the Touch's measurements except the headphone output appears to be capacitor coupled and probably lacks enough output for some popular headphones.

  41. This is certainly shaping up to be - without question - the best DAC bang for the buck (by a huge margin).
    NwAvGuy -- can you comment how you think it compares to new Audioengine D1 USB DAC (24-bit USB) which has good price point actually? Tx

    1. I'm not sure about the Audioengine DACs except to say, AFAIK, they're not designed in North America and they don't provide very detailed specs. It would be interesting to measure a D1. It might be in the same league as the ODAC or they might have cut corners or made some mistakes.

  42. Hi,

    You have ever tested professional equipment. I've seen a product that seems to have everything you need to get a stereo with the computer as a source: USB DAC, headphone amplifier and balanced outputs to handle a pair of powered speakers.

    It is also cheap and looks well built, the M-Audio Fast Track Pro:




    Please, can you include in your list of future tests? Seems very interesting.

    Thanks and happy days.

    1. @Juan,
      I have used many pro sound audio interfaces and natively that unit is only 16/48 unless you install drivers. Also, it's headphone amp is very lacking and has an output impedance around 33Ω making it bad for LowΩ phones and BA IEM's. Generally, the Fast Track® product is a cheap 'prosumer' audio interface for using ProTools™. Key word is 'cheap'. No real pros would ever use that interface for high end 2ch playback. Even the higher end Digidesigns/Avid MBox® line is severely flawed where headphone use is concerned. They are just not designed for use like an O2/ODA/ODAC, they are primarily designed as recording input devices, not critical listening.

    2. LOLOL, looks like you have a new protege called "FLAudioGuy"

    3. ...well, perhaps can be more interesting test the Focusrite Scarlett 2i2:


      Says 24bits 96kHz and less than 10 Ohm output impedance in the headphones amplifier.

      Happy days

    4. Sorry but even 10 ohms output impedance leaves most (> 50%) of all headphones out in the cold with compromised performance. Anything under 80 ohms, or any balanced armature headphone, will not be accurate with a 10 ohm output impedance. Focusrite, like most pro sound interfaces, pioritizes recording over playback. They took the cheap way out with their headphone output. See: Sonic Advantages of Low Impedance Headphone Amps.

      The Focusrite approach is fine for monitoring live recordings but it falls far short of what's required for high quality headphone listening with most headphones. It's also worth noting most Focusrite products require proprietary drivers under Windows. And, in my experience, their drivers are rather unstable and cause many problems.

  43. There seem to be already ASIO units out there that produce high-end DA performance. Seems like you goal is something that is generally considered (erroneously?) less desirable: non-bit-perfect DirectSound/WDM through the OS mixer. The complaints people (including myself) have with proprietary asynchronous ASIO drivers has little to do with non-ASIO performance, but is almost always tied strictly to ASIO playback and glitch-free recording capability... usually on slower computers or ones with cluttered drivers (i.e., not a dedicated workstation with a lean & optimized install). Trying to play DirectSound/WDM is rarely a problem for proprietary ASIO drivers regardless of computer or setup. ASIO would thus be a bonus feature in such cases as yours. I don’t understand complaints about something you don’t even plan on using. Having to download and install such drivers one time seems like a small price to pay for so much potential pro capability in addition to the simple Windows/Mac non-ASIO listening feature you're looking for in the ODAC. In other words, the pro devices can already do that and do so well even if they have issues with fulfilling their more advanced features on less optimized systems. Is driverless plug and play really that important to you that bit-perfect capability, inputs, and the other features cannot offset it if basic playback quality is as-good or better? Is Windows Mixer not really that destructive to the signal? It certainly does look like you will fulfill a niche for users that absolutely must have a 24bit plug and play non-ASIO DAC and nothing more. I wonder if you’ll end up with something that costs the same or more than competitive ASIO products, though, considering the cost overruns on the 02 compared to what was initially projected. Good luck, nonetheless. Looks promising.

    1. As I've already stated, Windows and OS X can deliver bit perfect audio with native drivers. I've verified as much several times. From what I understand, the main reason people want ASIO is for lower latency for simultaneous recording and playback. The ODAC doesn't record. And, for music playback only, latency is rarely an issue.

      You imply ASIO may somehow sound better. It won't. Some of the most highly regarded DACs around, including the Benchmark DAC1, use native OS drivers. Please see the Computer Audio links in the right hand column of this blog.

      You also correctly point out computers with "cluttered drivers" tend to have more problems. That's one reason I believe using native drivers is important. Why choose hardware requiring stability degrading drivers unless absolutely necessary?

      It's possible there may be third party ASIO driver support for the O2. There are only a few 24 bit capable USB interface ICs available that are suitable for this design. It wouldn't surprise me if there is, or will be, ASIO support for the chip in the ODAC.

      As for the costs, please remember the ODAC started out as an add-on to the ODA headphone amplifier. Those "competitive priced ASIO products" almost universally have horrible headphone outputs and most of the design budget goes into the recording, not playback, hardware. DIY and low volume production is rarely cost competitive with flashy plastic boxes mass produced in China.

    2. @Reticuli: No ASIO or ASIO4ALL drivers needed for playback only devices. Recording interfaces like an MBox® or Fast Track® may take advantage of ASIO drivers for low latency recording and simultaneous monitoring through the same device. If you are using such a device to record guitar, keys and vocals then you need low latency monitoring in your headphones to keep sync as close as possible. If you are simply playing back 2channel audio then no specialty (read: buggy) drivers are needed. The built-in UAC drivers are just fine and more reliable.

    3. @Reticuli: What "cost overruns" on the O2 are you referring to? I know of none, considering the O2 can be built in 3 variations, being, Battery Only, AC only and 'Combo'. From the start, the O2 has been described as $25-30 or $150 fully assembled from various providers. All of those price points have been met or bested.

      @NwAvGuy: Please feel free to embed this post into my previous one.

    4. Maybe that was just clarifying what the expected costs were? I've been following the O2 from the beginning and own one. I remember prices changing, perhaps an incorrect recollection. And I'm not pointing out the cost increases because these were particularly expensive or bothersome ones or being accusatory about honesty, but that there is an implying that there are no DACs in the ODAC's price range with similar performance. I don't think that's necessarily true, as one could have said about the O2 versus similarly priced headphone amps even after the pricing revisions. As far as price/features, the plug-and-play character of the ODAC is admittedly being put above recording, ASIO (at least until third-party drivers are available), and multiple ins or outs capability of competing pro interfaces. Yet one of the reasons for that: stability, is not a proven problem, as ASIO-capable interfaces seem to be rock-solid when used as ordinary Directsound/WDM stereo DACs. I haven't encountered DS/WDM problems myself and I haven't seen evidence for that presented in these threads. The complaints on the stability of proprietary drivers is pretty universally aimed at those interfaces’ advanced features on non-workstation systems. What I doubt is that such pro DAC outputs running as just DS/WDM are inferior to what is being designed here, cheap Chinese plastic boxes or not (the case/box doesn’t affect the sound, right?). What's been tested so far prior to the development of the ODAC are some rather crummy little USB outboard soundcards, several dirt cheap. And also, I suppose, since the ODAC is an add-on to a headphone amp (ODA or O2), I don't see how complaining about the headphone jack on a pro interface is relevant (even if it is substantiated) unless one were, for instance, to review an interface that cost the same as the combined price of an O2 and an ODAC together… or the ODAC has an O2 hidden in it that I haven't noticed thus far. Anyway, I hope the results of NWAVGUY's work turn out fantastic again. I'll buy one even already owning an interface just for the my gear-hoarding tendency. "Uhmmm... but I'm really a shepard." "No, the correct word is hoarder." I just don't quite see the magnitude of hole in the market that existed when the O2 was developed and filled quite nicely. It would also seem you get more for your money in some competing interfaces, assuming you don’t care about the box/case or the need to manually install drivers one time. The ODAC would seem be meant more for people who absolutely have no need for pro interface features and/or require a pretty box & plug-and-play. Hey, I’m all for a pretty box! But in my opinion, the stability and plug-and-play issues are being exaggerated, or perhaps a better way to put it: has not been convincingly asserted yet. And to the next poster "anonymous", I hope that wasn't directed at me. I’m not a competitor company with a grudge or a hater. "I'm a lover sweetheart, not a fighter."

    5. You said "What's been tested so far prior to the development of the ODAC are some rather crummy little USB outboard soundcards, several dirt cheap." Did you miss my testing the $1600 Benchmark DAC1 Pre? It compares well both objectively and subjectively (in preliminary blind listening) to the ODAC. The ODAC, under the exact same circumstances even has a bit more dynamic range than the DAC1. Do you really consider the DAC1 a "crummy little USB outboard soundcard"?

      Please remember the O2 and ODA came first and the ODAC was developed primarily as an addition to those. So the headphone output of other gear to which you might want to compare the O2/ODAC or ODA/ODAC against is relevant. And the output impedance of many pro interfaces can be found right in the specs so it's well substantiated. It was a logical extension to design the ODAC to also be used standalone, but you're correct, "the magnitude of hole in the market" for 24 bit USB DACs is not as obvious as the void the O2 helps fill.

      Many of the same issues apply to the ODAC as the O2. An obvious one is the lack of complete specs and/or proper measurements for a lot of DACs that are popular in the audiophile headphone community. Another is the number of "boutique" DACs that seem to be more about slapping some trendy chips on a board rather than an emphasis on proper performance.

    6. The DAC1 comparison isn't exactly relevant in demonstrating the lack of pre-existing similar-performance interfaces in the ODACs price range; rather it simply demonstrates the (wait for it... ) benchmark once again. I would argue the DAC1's performance was used to find suitable low-price USB DACs, but that it was put up against straw men. You then attempted to replicate or beat the DAC1's level of performance with a design of your own.

      High output impedance is not necessarily a design defect or performance reducer on headphone jacks. It's just a problem with specific headphone transducers of lower impedances, right? And as I stated, I'm not disputing that many interface jacks are poor even ignoring their impedance. Even if their general crapulence is substantiated (which we can hypothetically suppose for the moment is universal), the ODAC doesn’t even have a headphone jack, right? But some of the interface headphone jacks that are fair quality and higher impedance are capable of doubling as line-outs at nearly the same performance level as the main outputs. And as you state, the impedance of the jacks is often disclosed in the specs to begin with. An extra independent DAC channel pair that doubles as a possibly decent jack for high impedance cans (even if they need to be sensitive, too) doesn’t seem like a negative compared to an ODAC with only one DAC channel pair and no headphone jack at all.

      One curious thing about Windows mixer is it has that shared and exclusive mode aspect, and it doesn't seem to do very well in the areas of IMD and high frequency extension if you feed it (within the Windows software domain from an app) one bitrate while the shared mode is set to something else. It appears to get quite mediocre trying to deal with converting two sample rates very close together, such as 44.1 and 48khz, and still is not very competent with just doubling the sample rate. You can manually go in there and make sure the sample rate is exactly what you plan on playing back. However, if you don't do that and you aren't using either ASIO, an exclusive WASAPI driver, or have a software player that can do WDM/DS exclusive (don't know of any that do and prevent other programs from running... kernal drivers maybe?), the performance seems to suffer if this setting isn't matched.

      Do you have any solutions for dealing with this or do users just need to manually change the shared mode to whatever the file's bitrate is?

    7. I've never said I'm a fan of operating sytem sample rate conversion. I think most would consider setting a single Windows Control Panel option less of burden than installing a third party, potentially problematic, driver. For those who want to geek out on the specifics, there's a link in the right hand column of this blog titled "Computer Audio Setup Guide".

      The fact is 99% of the music we all listen to is in the Redbook CD 16/44 format. Sure there are some who listen to DVD soundtracks that are 48 Khz but they're often lossy compressed audio and resampling is probably the least of your worries. And there are a few who buy some of the very limited selection of 24/96 downloaded music but that's more a novelty than anything else. A musician recording their own hi-res music probably doesn't need an ODAC.

      So the bottom line is 99% of people can likely "set and forget" Windows to 24/44 with the ODAC. It would seem you're in the minority. Most believe the benefits of driverless operation far outweigh the re-sampling issue for those very few cases where it's an issue.

      And, as I said in my previous reply, it's likely there either are or will be ASIO drivers that work with the ODAC. Wouldn't that address all of your concerns? Why are you still beating the horse?

      As for output impedance I'm not sure if you haven't bothered to read my article and the Benchmark article on the topic, or if you're just trying to fuel an argument. This article clearly shows, even with 300 ohm Sennheiser HD650 headphones, that lower impedance outputs have significant advantages:

      Sonic Advantages of Low Impedance Headphone Amps

      As I also explained above, the ODAC is MAINLY intended to be an addition to the ODA and O2 forming an integrated headphone DAC. So, in my opinion at least, the headphone amp performance is important and valid. Despite the made-in-China volume production advantage of pro gear, I'll put the ODA+ODAC up against any pro sound interface up to twice the price and the headphone output will probably beat nearly any pro sound interface.

  44. I love how as soon as you bring a new product the bashing and hating of nwavguy begins X-D

  45. Thank you NwAvGuy for a great reading. All things are looking good except one. Maybe I didn't catched something but here is my question. Only ine thing bothers me here and it is the volume control: what type of control it will be and will ODAC have an external pseudo pot to control the volume or some software to control volume in OS? Now don't get me wrong, I don't have anything against digital volume control and on the contrary, I think digital control is the right way to go! I just wonder how convenient will be volume control on ODAC. I am planning to use "The Wire amplifier" from DIYaudio.com and use it in POTless mode. I have seen you NwAvGuy on diyaudio forums and I think that you understand me. Some well known DAC chips like WM874X and es9018 support proper digital volume control, are you going to implement native digital control in ODAC? Pseudo pot would be cool to see on ODAC front panel. I saw this idea at twistedpear http://www.twistedpearaudio.com/control/volumite.aspx it is nice, small and simple. Hope you can use this idea in ODAC or maybe even better one.

    And the second question is regarding opamps. Will ODAC have opamps in dip8 sockets to support opamp rolling? (There are some good opamps like LME49990, LME49710, OPA1611, OPA1632, AD797 that I've seen in a lot of expensive gear, amybe they can help to improve the ODAC performance. Don't get me wrong here either: I've read your previous articles. Just curious if these opamps can help good thing to become even better.)

    P.S. Very interesting project. Wish you all the good luck out there! Best regards!


    1. The ODAC started out as an add-on to the ODA headphone amplifier. It also works with the O2 headphone amplifier. Both of those amps, not the ODAC, have the volume control. The ODA will also have a volume controlled line output.

      While digitally controlled volume controls have some benefits they also generally require a microprocessor, some sort of display, etc. Some are also inferior in their performance (lowering bit resolution and/or adding distortion and non-linearities). Microprocessors require firmware, programming, add cost, take up board space, create more digital noise, etc. They're also usually more annoying to use than a pot. If you look at the original O2 article and measurements you'll see the pot used (the same one that's in the $1600 Benchmark DAC1 Pre) performs very well all the way down to -50 dB.

      There are "modular" electronic volume controls out there that could be added to the ODA by a DIYer if they really want one. Using just the volume control in a DAC chip prohibits having a line level input as it only controls the DAC volume. The O2 and ODA both have line inputs.

      Op amp rolling is mostly myth and often does more harm than good. Please see my Op Amp Myths Article for why and a $500 listening challenge that nobody has taken me up on. Plus, the ODAC is entirely surface mount to keep the profile as low as possible to allow it to "piggy back" into other designs more easily.

  46. Is there any place on the board to include an USB isolator like ADUM4160?
    I suppose it is fairly easy to use with not many parts needed.

    1. There's not. Because the ODAC is USB bus powered you can't isolate the USB bus without an isolated power source to power the ODAC. And, for nearly all headphone applications, it won't make any difference. USB isolation is only of possible benefit when you have grounded equipment downstream of the DAC (such as an A/V system, etc.). That's one reason few USB DACs, including the Benchmark DAC1, have USB isolation.

  47. Hi NwAvGuy,
    Thank you again for your hardwork and kindness in sharing. I can't wait for the ODAC to come out.

    In the meantime, if you have a moment to spare, I shared my latest DAC design at diyaudio.

    You can contact me via the forums for technical discussion if you like. It shouldn't compete with the ODAC because I'm not offering any kits/boards/group buys.

    Thanks - Arius from diyaudio

    1. Thanks for sharing. It looks like a nice collection of chips. Like you, the Benchmark DAC1 was partly my "inspiration" and I agree with at least some of your design goals. I'm not worried about competition but instead I'm mainly trying to raise the price/performance bar.

      Your design is considerably more complex, expensive, and involved than the ODAC. As you point out in the thread, it requires firmware, programming, challenging SMT soldering, etc. It also, unless I missed something, has not been properly measured. I can attest even making a "best effort" at PCB layout, grounding, etc. often doesn't yield anywhere close to the expected results.

      We're on our fourth revision of the ODAC PCB and we both are probably more experienced at PCB layout than most DIYers. If I didn't have an audio analyzer to discover all the layout problems, we probably would have stopped at the first revision.

      My other goal with the ODAC is to use it as the baseline for some serious blind testing against much more elaborate designs like the Benchmark DAC1 and whatever else I, or my partner in crime, can get our hands on. If we find other DACs that stand out in blind testing I plan to dig deeper with measurements to hopefully explain the audible differences. If we don't find audible differences then it's hard to justify a more expensive and/or elaborate design than the ODAC.

      We also had reservations about the TAS1020B for a production board as it's going to be discontinued and is not recommended for new designs. It also, as you comment in the thread, requires firmware and programming to properly support driverless asynchronous mode. If your firmware proves to be solid, and you release it into the public domain, that might make the TAS1020B more attractive--at least as long as they're still available.

  48. The transient response is a major failing point of almost sigma-delta audio DACs. Does the ODAC address this issue at all? While there are many flaws with non-oversampling filterless R2R DACs, I think there is some merit to the claims that their sound is simply more natural than modern DACs, and this can be seen from the time-domain performance.

    The argument most often given in support of extreme oversampling and harsh digital filters is that the I/V conversion and amplifier circuitry after the DAC cannot handle the harmonics. This seems wrong, as modern opamps have bandwidth into the megahertz range. The harmonics created by R2R architecture are also easily handled by slow-rolloff analog filtering with suitably high cutoff frequencies (with some extra margin on top of the Nyquist frequency).

    Then many designers make excuses to avoid using amazing (IMO) chips like the PCM1704 that they require too much support circuitry. There's a new chip I think it's very cool called the ARDA AT1401. I hope someone someday makes a R2R-based DAC with USB interface that has as much effort put into the design as the ODAC.

    1. This is an interesting topic and worthy of its own article someday. Ideally I would like to add something to the debate rather than merely re-state what's already been published. That will require some more research on my part and I have some theories and ideas I would like to check out.

      DAC and digital filter design involves trade offs. There's no perfect real world solution. Some of the best performing DACs at any price, several of which have also received very favorable subjective reviews for their sound quality (such as the Benchmark DAC1 and many others), are sigma-delta DACs using linear phase filtering.

      Non-oversampling DACs generally perform horribly on the 19Khz + 20Khz CCIF IMD test. This can be seen in some of John Atkinson's reviews at Stereophile. Some of these DACs have hundreds of IMD products below 19 Khz over the maximum desirable limit of -80 dB. Collectively these distortion products sum up to lots of distortion (well over 0.1%) that's potentially audible. I'm not talking out of band components, or slew rate op amp problems, just really poor IMD performance by the DAC itself as you approach the 22 Khz Nyquist frequency. This isn't an excuse, it's just reality and there's no cure for it. R2R DACs also often perform much worse for low level linearity regardless of how they're implemented. These are significant trade offs.

      I'm not aware of a single credible blind test that shows any audible benefit to different filtering schemes except a few artificially synthesized tests or where more is going on than just different filtering. So, AFAIK, the "inferior transient response" (i.e. ringing) has not been demonstrated to be an audible problem. If someone knows of a credible blind listening test that demonstrates the superiority of hardware non-oversampling or hardware minimum phase filtering, please post a link here?

      The ODAC, like 95+% of other current DACs, uses a sigma-delta DAC. And like perhaps 90% of current reasonably priced DACs it uses linear phase digital filtering. I'll be publishing a graph of the transient response which looks pretty much like the Benchmark DAC1 and countless other well respected DAC's transient response.

      In my experience those who prefer obsolete technologies often tend to own those technologies and hence are biased towards defending what they own. There are still people, for example, trying to claim component video is better than HDMI. But if you pry a little deeper you find out they bought a $30,000 projector that's so old it lacks HDMI (or DVI).

    2. I agree, this is an interesting topic. I dont think oversampling is a problem at all compared to "time-smearing" digital filters. I am not trying to discredit your design by any means - like you said, I haven't seen any definitive tests either proving the audibility of differences in transient response of DACs. That said, on an intuitive level, an oversampled R2R-based DAC with a conservative analog filter may offer the best of both worlds (time domain accuracy and low distortion). Do 24-bit (or higher) R2R DACs still have linearity issues?

    3. @Anon, if you know of any objective blind tests that support your belief that old school R2R DACs are somehow better, please post a link? Otherwise, I have to believe modern DACs are the better overall choice. If I'm forced to choose between mostly ultrasonic transient response ripple or massive IMD below 20 Khz, I'd pick the very likely inaudible ripple. If someone has a good argument for favoring the ripple over serious alias distortion, please post links that objectively support your argument.

    4. The IMD is only a problem for non-oversampling setups, according to your original post. I think a fairer comparison would be a delta-sigma vs. reasonably oversampled, maybe 4x, 24-bit or higher R2R DAC.

      In addition to ultrasonic ripple, the actual SHAPE of the transient response (in the time domain) is altered under digital filtering. Again, I'm not sure this is audible, but a comparison on objective terms would definitely be illuminating.

      Just because a design is old doesn't make it obsolete. Sometimes "improvements" in design are really just improvements in cost-effectiveness, and overall performance declines.

    5. All fair points. I especially agree sometimes "progress" is much about lowering costs as anything else.

      I haven't done that much research into what R2R DAC chips are still available. I do have some flagship Burr Brown R2R DACs in a couple of vintage high-end CD players. But I don't think I have any DACs with an S/PDIF input that are R2R. That makes a proper time synchronized blind comparison more challenging.

      I'm 99.9% certain the DAC used in the Meyer & Moran blind listening AES study was sigma-delta. It proved to be transparent under normal listening conditions--i.e. it (and the companion A/D) did not alter the sound in any way over 60 audiophiles, recording engineers, and college students could reliably detect over 550+ trials.

      In terms of overall measurements the flagship AKM sigma-delta DACs, for example, are hard to beat. As I said I agree it's an interesting topic and more blind listening tests might help shed a bit more light on the subject. But I would need a suitable R2R DAC--ideally something that's currently available and modestly priced.

  49. nwavguy,

    I saw a guy claiming to get better sound off of internal drives that were separate from his OS drive and also claiming to get much better results from an internal drive stored in an external enclosure. Should I make an effort to store my media externally?


    1. There are also guys claiming setting a Sonic Brick on top of your amplifier makes it sound better. The only real-world issue I'm aware of with hard drives is when drive access creates audible noise and that usually only happens with built-in motherboard or soundcard-based audio. There have been a few reports of drive access noise on external USB audio devices but the ones I've seen involved rather sketchy USB DACs and probably lacked decent power filtering.

      There are only three things hard drive noise in a PC can effect:

      - Audible noises as discussed above.

      - Dropouts due to insufficient bus or CPU bandwidth. This would be an obvious problem.

      - Increased jitter but this is extremely unlikely with any decent USB DAC as the DAC has its own local data clock. It is somewhat more likely an issue with internal audio, or using a PC's S/PDIF output, but even then it's likely rare to non-existent.

      In general, if you can't hear any random noises that seem to coincide with drive access, don't worry about it. If you can, you should look at upgrading your audio hardware rather than adding another hard drive.

    2. The other and probably most common issue is the mechanical sound of the drive access itself, potentially an issue with open headphones and some computer and living arrangements. Try silentpcreview if you want to see acoustic analysis of hard drive seek and idle noises, as well as ideas and builds to reduce those noises. With an external drive located further away from your ears, I guess you could get reduced noise. ;)

      Some audiophiles have the weirdest conceptions of what matters. Sometimes these mature into irrational fears of forward error correction (FEC) or ideas that lossless audio formats sound different, among other things. Who knows.

    3. Well,

      I have to add a new drive one way or another. I'll probably grab a 2tb drive for just media, and another 2tb drive to toss into an enclosure and use for back ups (i have serious trust issues with "external" hard drives. Any suggestions on hd's? I know its terribly OT. Also, thanks for the reply :)

      @mike, I do use open headphones, and I can hear my computer.. mostly just a bit of fan or cd/dvd drive noise.. my computer was pretty darn silent until I upgraded my cooler. I think I will look into quieter CPU fans.

    4. @Chris Langley

      You could try the new Seagate 1TB/platter drive. It's the drive with the ST2000DL003 code. But really, Anandtech/Techpowerup/SPCR/others is the correct place for asking this.

  50. Just wanted to say 'thank you' NwAvGuy; your hard work, integrity and dedication makes you one of the few (if only) bonafied heroes of the wonderful and wacky world of hi-fi-dom.

    If there were to be a college course on headphone hi-fi, this blog would be in the first week's curriculum.

    It's sad to see the trouble that comes your way due to your willingness to stand up for something other than someone else's bottom-line, but for all of us who have read a history book or two the results aren't far from surprising, although your courage to stick by your guns is. Basically no one has delivered a spectacularly awesome message without having to beat back idiot minded nay-sayerers, and the more idiots whining, generally the greater the message, so perhaps the golden lining might be that you've stood tall, held your ground and so far the people who've tried to pee on you parade have only validated in some way what you had set out to accomplish.

    In the words of the holy order of the Wu-Tang Clan; Cash Rules Everything Around Me; I hope you find some way to channel all this and to tie it into making some sort of living from it; you've certainly proven more than capable, and from a selfish stand point, without it lining your pockets, the knowledge and effort you've poured into this blog and projects is too much for anyone to sustain without something 'objective' to show for it. It's 2012, Well Fargo doesn't deposit good will, and dude, people get paid a whole lot more to do a whole lot less.

    And I know I'm not the only one seeing you kicking ass and taking names, don't get discouraged along your way.

  51. I have tremendous respect for your work. Thank You!

  52. Things are really looking good.

    To be honest, your challenges have got me a bit excited, and perhaps not with entirely pure thoughts. With all this hyped gear I would so love to see people being unable to tell supposedly choice gear from things you can (at least partly) put together yourself for a few hundred. You mention gear for $450, but considering your claimed measurements and what's humanly even audible one can't help but fantasize about seeing it invalidate the existence of gear into the range of thousands ...

    But enough of the praise, on to the part where I want things from you:
    I've got my eyes set on a Sansa Clip, and while I want the features of the Zip I don't want to miss out on the sound of the +, so I wanted to know if you have any idea when we will get your word on that? Will that be left until you are finished with the ODAC?

    1. I not only have the ODAC but also the ODA. But I've been curious about the Zip as well. I'll try to squeeze measuring it in somewhere. If it performs very similarly to the Clip+ that makes the review a lot easier to write. If it's much different, it's going to be a lot more time consuming and might have to wait although I should be able to at least give a brief preview and let everyone know if it's much worse, similar, or, better.

      As for blind tests I agree it could lead to some very interesting things. But doing blind tests in a way that can stand up to criticism is challenging. If the tests reveal no discernible differences, and history is any guide, critics are likely to attack the test methodology. The best solution, in many ways, is to challenge the most outspoken critics to a public blind test that's on as many of their terms as possible--i.e. their preferred headphones, music, cabling, etc. But, history also predicts, they will find reasons to avoid backing up their critical words with their own ears. So readers may be left to decide which side has the more credible position.

      It's also possible more thorough blind testing may reveal audible differences. If that happens I'll be very interested to see if the right measurements can provide an explanation. Such differences would also provide more incentive for a future "ODAC+" to raise the bar higher. But, for now, it's best to start with a simple relatively low cost design and see if it can clear all the hurdles.

    2. I'm also very interested in the clip zip.. Maybe squeeze it in between the odac and the oda? seems like a good spot for a little break from designing. I'm sure everyone will be busy playing with the ODAC for a while after it comes out.

  53. In case I want to get the most of the ODA+ODAC as a preamp, is there any specific way of optimize it for pre duties? will this customisation penalize the head-out performance?

    1. By popular demand, the ODA will very likely have preamp outputs on the board. Both the headphone and preamp outputs will already be optimized with no modifications required. In the interest of the best performance and keeping the cost down the the preamp outputs will likely always be enabled. If you use the ODA to drive speakers, and want to listen with only headphones, you will need to turn off your speaker amp, receiver, powered speakers, etc.

    2. Just wanted to say I'm very glad to hear this. I've been reading your blog ever since I found out about the O2 and I'm patiently waiting to buy an ODA when it's available and I'd be horribly sad if I couldn't use the ODAC with my stereo.

      So please keep the pre amp outputs or at least make that an option that costs more if anything :)

      I appreciate your work and writing, thank you.

  54. Do you think the ODA/ODAC will offer any sonic advantage over the O2 with ODAC installed, via headphones? Or maybe that is too hard to call at this stage of development?


    1. Unless you can benefit from one or more of the ODA's added benefits over the O2 it's unlikely you'll hear any sonic difference. The O2 is a very transparent headphone amp and it's hard to improve on that in terms of sound quality. The ODA is planned to have more flexible gain options, a 1/4 inch headphone jack, RCA input jacks, preamp outputs, and more. But, assuming the O2's gain is reasonably correct, it's unlikely the ODA will sound better in most circumstances. I plan to compare the two in blind listening tests against each other and some much more expensive options. Regardless of the outcome I'll report the honest results.

  55. This article addresses a very interesting topic:


    Before you connect anything to your laptop/netbook, we should eliminate the noise source due to the topology of the power connection. The same article explains the easy solution: replace the power cord of two conductors by one of three conductors, and make the connection between the negative and the earth in the power connector on the laptop/netbook.

    An easy and inexpensive way to enhance any laptop/netbook as audio source

    This text explains the same noise problems due to bad topology in the suplies. In Spanish:

    http://www.mediafire.com/file/o1gn2inmn3i/Simple DOA & Clean Supply.pdf

    Happy days

    1. It's really interesting how my HP portable adapter has 3 prongs and many VAIO portable adapters only have 2 prongs.
      Why? Is this because of the grounding issue?

    2. What matters most here is if anything downstream of the laptop/computer is grounded. Most headphone amps are not grounded so it doesn't matter if your PC/laptop is grounded or not.

      If you're using audio/video gear that IS grounded, then it might be useful to either isolate the USB connection or otherwise isolate the grounds between the PC and audio equipment.

    3. I found the Audio Component Grounding and Interconnection article from DIYAudio.com to be a fairly easy to understand primer on arranging/understanding grounding schemes (and clearling up a lot of the confusion I had related to what "ground" actually means) and how two devices can work fine separately, but when put in series (preamp and power amp, for instance) there are suddenly ground loops, buzz, hum, fire, brimstone, etc.

  56. have you ever experimented paralleling dac chips?

    1. I have not. It's been demonstrated DACs can be audibly transparent without resorting to multiple DAC chips or other exotic configurations. I think most such DACs are designed that way for marketing and/or snake oil reasons. Some of the best performing DACs at any price use just a single DAC chip.

  57. Hi NwAvGuy, I hope all is going well for you. I don't know where to post this, so move it to a different spot if you please. I was wondering if you ever measured the audio output from an Apple AirPort Express. The 3.5mm output is both analog and optical. For only $99.00, it might make a good wireless audio streaming device to play into the analog input of the ODA or O2. The specs don't mention if the stream is 24 bit or 16 but seeing as the iPad2 is 24 bit, there may be hope? I could see a case for playing my music from iPod, iPad, iPhone (or even an iMac) wirelessly while reclining in my chair and directing it all the the Remote app.

  58. I've got a couple of questions I was hoping you could help me with.
    First question being about DAP's and DAC's. I recently broke my Clip Zip, and before that the jack on my Clip+ stopped working. My main concern is SQ, and you've commented on the Clip+ having a decent DAC. My questions regarding this are: Do you think there are better DAP's out there (taking into consideration money) or do you think I'm better off buying another Clip and using the money that would have been spent purchasing a more expensive DAP towards other audio gear. My second question related to this is, will the ODAC be compatible with the Clip?
    My final question is regarding the O2 and the ODA. If I'm not going to utilize the higher quality inputs/outputs and don't mind having an external DAC/portability/ergonomics, do you think I should wait for the ODA or get an O2 now?

    1. If your amp isn't going to move around much, I'd still wait for the ODA. If you might get some benefit from a portable amp, or just can't wait, I'd get the O2.

      None of the Clip players have a digital output so they can't use an external DAC--including the ODAC. The O2 and ODA are compatible with the Clip.

      The SQ question is hard to answer. The iPod Touch (and perhaps other current iPods) have better DACs and audio performance. But the Clip has a lower output impedance which can be a big help with many headphones. If you're going to use an amp with the DAP, like the O2 or ODA, I would go with the iPod if you want the best. If you're mostly going to use it standalone, I'd probably get another Zip or perhaps a Clip+.

      My Clip+ has had over a year of frequent use and I've not had any problems with it beyond the battery run time being a bit shorter than when it was new. With frequent use, you'll be lucky to get more than a couple of years from any DAP before you start having battery trouble. The Clip is so cheap it's easier to consider it disposable--especially compared to a $200+ iPod. And, based on what I've seen, I would stay far away from the players that are even more expensive--like the clunky HiFiMan players.

  59. @FredM, I really don't want to get into a debate about subjective tests, but good subjective tests do indeed work on difference, rather than preference. Take a look at BSD1116, for instance.

    While ABX is the poster child for pure difference detection, it does require extensive training and familiarity with both material and the system, even when A and B are both known (reference and test signal) and fixed.

    For some things, signal detection (single blind but computer administered so it's an equivelent thing) are better, they are substantially self-training, basically you learn during the test what you're trying to hear, but they are sometimes hard to create for some kinds of impairments.

    There's a lot more to be said, but perhaps this isn't the place, my only point is that a proper subjective test can determine strictly if a difference is audible. Nowhere, you notice, did I say "easily" or "trivially", such tests are neither.

    Having said all that, I agree entirely that engineers and scientists need to make sure that they are chasing real effects, not the fruits of perception, which can be fleeting indeed.

    1. Good subjective tests first identify if there are audible differences and, if there are differences, the next step is often to identify a preference. If no preference can be determined, do you strive to make A more like B or B more like A?

      In the infamous Carver Stereophile challenge, Bob Carver added tweaked his $700 solid state amp to sound identical to a $3,000 Conrad-Johnson Premier Four tube amp, and amp which the Stereophile staff felt sounded "much better." Many of the changes he made degraded the measured performance of the Carver amp, rendering it less accurate. But the panel preferred it to the more accurate version he started with.

      That's the problem with making things that "sound good" -- what sounds "good" might be less accurate. Then you've taken a step backwards, albeit often after a lot of work.

    2. And I believe the "monoblock" CJ amps were $3K each so it was really $6000 vs $700. Given all the "dancing around reality" that was done by Stereophile over that challenge those involved should have run for US Congress. And, not surprisingly, to my knowledge they've never attempted anything similar since.

      Your points are valid. It's easy enough for a blind test to demonstrate there's an audible difference. But trying to choose which was one is better is like choosing between two similar wines in a blind wine tasting. If you had a large number of listeners/tasters sometimes a clear preference might emerge. But the outcome can also be more equally divided. Joe Wine Snob can have a strong preference but he might like his wines more dry or tannic than Joe Average.

      In my experience with blind testing, even when there's a difference, it's difficult to pick a favorite--especially if you still don't know which is which. I might think I like the midrange clarity of A better but the highs seem to be cleaner with B. So from there it can come down to what music you're listening to, etc. The choice is rarely obvious.

      The above is fairly dramatic when you stop and think about it. Because the sorts of clear "across the board" improvements so many claim to hear when they compare say DACs are, in reality, quite rare when you don't know which is which. Even when differences are detectable, it's often hard to pick a favorite unless one piece of gear is seriously awful.

      But let's save this dialog for a future article (or the existing Subjective vs Objective article). We keep hitting 200 comments here which seems to be the limit.

  60. The first out-of-the-box (i.e. without modding) Android device able to output USB audio is the Android 4.0 powered Archos G9.

    There is an ongoing lobby requesting Google to impose USB DAC as a standard Android USB device, like a standard USB device for every Mac or PC (i.e. we don’t have to request each individual PC manufacturer to add the USB audio capability).

  61. I have a question: did you make a blind test between clip+ vs the ipod + o2 driving iems? Where there audiable diffrences?

    1. Comparing two players blind gets complicated as you're normally just trying to see if a difference can be heard. Unfortunately, it's nearly impossible to play two different portable players in near perfect time sync. That means in real time A/B comparisons you'll always detect a difference--one player will be slightly ahead of the other in time. This would happen even comparing two identical players.

      I do most of my blind testing using an ABX box so I can do it solo. This method works great for things like amplifiers, cables, and even DAC's when they can be fed the same digital signal and have similar latency. But it doesn't work where there's a noticeable time shift.

      That's a long way of saying I haven't done a blind comparison of the Clip+ vs iPod. It is, however, relatively easy to ABX compare the iPod's "raw" headphone output to the iPod running through the O2 amp. I have done those sorts of blind tests and the higher output impedance of the iPod with my Etymotic or SuperFi balanced armature IEMs creates an audible difference.

      Comparing two players blind you would ideally need someone else to run the test so you don't know which is which. You would have to account for the inevitable time shift using methods such as repeating the track each time you switch. But that's a much less sensitive test than direct real time A/B (i.e. you're less likely to hear differences).

    2. I don't know how easy it would be with your ABX setup - but I think a solution would be to make sure that the players are close enough to being synced (it's probably easy to get less than a second of delay just by pressing "play" on both at the same time) and introduce one or two seconds of silence each time you switch. The comparison wouldn't be as good as switching instantaneously, but it might be better than replaying the track from the beginning?

  62. This may be abit premature, but I'm curious how you're going to choose who gets to manufacture and sell the ODAC. Normally, you will sell your design to the highest bidder but since you don't sell your designs (I would have been perfectly fine if you had chosen to make money off these projects, afterall a guy deserved to be paid for the great work he had put in!), I'm just wondering what criteria you will have.

    On a completely unrelated note, can I just ask your thoughts on digital transports for iPods? From my understanding, a digial transport should ideally be able to draw out the digital signal from an iPod by bypassing the internal DAC totally. Hence, theoretically, there shouldn't be any difference between a $100 transport, and a $500 transport. Can you comment on whether there really isn't any difference (besides the different built in DAC units) among the many digital transports on the market today? (Like a $500 transport will do a better job of bypassing the iPod's internal DAC as compared to a $100 transport?) I was thinking of having a digital transport for the ODAC and ODA but this question has been bugging me for a long time. I've gotten many replies that there is no difference, but there wasn't any hard data to back it up. Thanks!

    1. The ODAC manufacturer for the first batch has already been determined because they have already invested a lot of time and money into helping develop it. Once the initial production run is sold ou,t and their development costs have hopefully been recovered, we will know a lot more about demand, possible revisions/updates/enhancements, etc. At that time we can mutually figure out what makes the most sense for future production.

      I haven't personally tested iPod docks with digital outputs. The only difference between their digital outputs, if any, should be in jitter. I don't know how much digital output jitter the various iPod's have to begin with. If there's a lot it's possible some docks could use more advanced methods to reduce the jitter (like ASRC).

      Overall, given the respectable analog jitter performance of the iPod, I would NOT expect an audible difference between the digital outputs of different docks. But I can't say for certain there isn't any.

  63. If anybody wants to know how to hook up the ODAC to an iPad, you need the following items:
    -iPad Camera Connection Kit (from Apple)
    -Split USB Cable with distinct power end (if ODAC has a type B USB connector then check out the Cables to Go 28108 as an example)
    -USB Power Supply (iPod or iPad power brick, or powered hub, or Energizer XP4001)

    In case people are curious, this setup can also be used for recording onto your iPad with a USB microphone.

  64. To update my last comment, it appears the ODAC uses a mini-B type connector, so to hook it to an iPad, you'll want a cable like the Cables to Go 28107, not the one I mentioned above.

  65. I'm very like your explanation about how to develop good amplifier, actually I have O2 now & I like it..

    I have some questions about your upcoming amplifier ODA:

    Is ODA is bigger than O2?

    and has ODA integrated with ODAC when it produce? So if we don't use ODAC there will be empty space in ODA?


    1. Yes, the ODA is bigger than the O2 to allow room for more options such as 1/4" headphone jack, RCA jacks, preamp output, etc. The ODAC board is the same as used with the O2. It can be added later to the ODA if desired or you should be able to buy a complete ODA+ODAC.

  66. I wonder if you can compare between ODAC and amb gamma2,

    maybe it'll be interesting.

    Have you been looking for amb gamma2 design, is there any flaw in the design (since it was diy)?

    1. In the article above I point out some of the problems with the gamma2. Most notably it uses an ancient USB interface that's limited to only 16 bits, it uses distortion producing electrolytic coupling capacitors in the line outputs, and it falls well short of the Redbook standard of 2 Vrms output. I guarantee the gamma2 will measure significantly worse than the ODAC.

  67. A little off topic, but I'm wondering if you happen to have looked at the XMOS Reference Design Board. It is $149 at Digi-Key, and offers i2s and coaxial S/PDIF up to 24/192 and TOSLINK up to 24/96. It also has a built in DAC and ADC, with analog inputs and outputs. I am considering getting it to use as a USB-i2s and S/PDIF converter. There are a lot of $400+ USB-SPDIF converters that are using this chip. I think that this board has a lot of promise, but unfortunately I haven't found any published measurements. There is also a $349 evaluation board that offers multichannel input and output. Please excuse me if you have written about this board before and I have missed it.


    Thank you for your continued work, I greatly appreciate your efforts and am enjoying my O2 amplifier.


    1. The XMOS board is not off topic, and it has been (briefly) discussed here in several places. The big problem is it requires a proprietary driver for Windows and that driver cannot legally be re-distributed without paying a license fee. I'm not a fan of proprietary drivers in general for a variety of reasons. But if you're OK with using the demo driver it could be interesting to mess around with. But the ODAC board will be less expensive if you don't need S/PDIF and the other features.

      Generally demo boards perform fairly well so the odds are good the XMOS board has at least reasonable performance. But it won't fit inside the O2 or ODA and doesn't have a quality headphone amp. And the driver issue is a deal breaker for an under $100 low volume DAC like the ODAC. My experience with similar proprietary USB Audio 2 drivers for pro audio interfaces in Windows has not been good. The one from Tascam is especially a train wreck.

    2. Thank you for taking the time to respond. I use OSX for audio, so the drivers are not an issue with the XMOS board. I understand your reservations about the software for the XMOS. This platform is being used in a lot of expensive upcoming and already released products, so it must have some advantages over other platforms. I think I'm going to buy the board and give it a shot. It does a lot for the money.

      Of course I am going to buy the ODAC when it is available, probably even more than one if I can get them.

      Feel free to delete this if you need to save space, I just wanted to thank you for your time.


    3. "This platform is being used in a lot of expensive upcoming and already released products, so it must have some advantages over other platforms."

      If you want to sell to audiophiles, you need shiny USPs. It's not enough to cleanly convert from digital to analog, you need to convert with authority thanks to the Awesomium (TM) cryogenically-frozen capacitors in the power supply! And the free silver power cord! OK, the examples are OTT but the point stands. Nobody ever sold audio equipment by pointing out how well they routed the star ground.

  68. Dear NwAvGuy,

    this question is probably off topic and maybe has been already answered...

    Would you recommend ODAC + some high quality reference headphones to be used
    for mastering purposes?

    And I'm curious what do you think about the so called mastering engineers (I wouldn't
    mention which popular forum they're active on), who say that the absolute ruler flat mastering experience currently is using a very expensive reference headphones and a very expensive balanced headphone amplifier, together with the headphones being balanced-recabled with custom military specs audio cable, which are giving better and fuller low end and mids to the headphones than the stock cable. Well, for myself, I absolutely wouldn't trust such engineer and would never give them anything to master, for such claims. I think that a serious mastering engineer would never say anything like this - balanced recabling that gives a better, fuller sound... are they strongly biased or what? That's just funny :)

    Btw, I'm a happy user of the O2 and currently waiting for the ODAC. Thank you for all your hard work being done on O2 and ODAC :)

    With best regards,

    1. Mastering/recording engineers are not somehow exempt from hype and myth. Their hearing is subject to the same unavoidable bias as the rest of us. So, like audiophiles, many believe spending more money generally yields better sound even when it doesn't.

      Several of the AES blind studies included engineers involved in audio production. And, while they were often more able to pick out subtle differences, they also failed to hear the difference between things they claim to easily hear in their jobs. For example Meyer & Moran's study used recording engineers to compare SACD to 16/44 CD quality audio and they could not tell which was which.

      My experience is those working in music production, as a group, are a bit more rational than hardcore audiophiles. They're less likely to buy Sonic Bricks and $4000 power conditioners. But, like audiophiles, many have a gear fetish and want to believe really expensive hardware sounds better even when it doesn't. Pro audio has its own snake oil. Avalon is a good example.

      I'm not the best guy to ask for headphone suggestions. If you don't need isolation I personally think the Sennheiser HD-600 is a great headphone for mastering. Some of the better Stax headphones, or the AKG Q701, might also work well. In a closed back headphone it's harder as all the ones I've heard have various obvious flaws (especially the classic HD-280 and HD-380). I would probably lean towards the Denon AH-D2000 (or one of the higher models) just because I know them well. But they have a bit of a "V" shaped response and boost the bass and highs.

      AKG, Shure, and Audio Technica all make some nice closed back headphones. I'm also told KRK has some good cans for studio use. I'm not sure what the Mackie or Genelec studio monitor headphone equivalent is.

    2. Pro audio is surely full of snake oil, just as the consumer market is! Avalon 2022 can't begin to compare to the Benchmark MPA1 in most respects. What happens is that one guy uses it and says how great it is or some biased review in a prosound rag or forum. Then impressionable lemmings follow suit. For $3k you can get less performance with an Avalon than $1.8k with an MPA1. I do like some outboard mic preamps because many mixers/control surfaces have "less than great" built-in pres. It's not like you're gonna get a Cadac, Neve, Neumann or even a Midas pre in your MBox Pro or Mackie whatnot. Alot of newer studios are going with an Avid C|24. Even at say $10k, expensive for consumer but cheap for studio, it doesn't even have a pre as good as an MPA1. Get the recording as best as you can, cuz even Pro Tools can't fix what's missing.

      As far as mastering goes... I doubt any mastering engineers worth their salt and/or multiple Grammy winners use headphones to master with. They may use them to check for certain things but their needs are so different than the studio recordist. Mastering is the audio (or video) post production that gets the mixer stems in the original format and makes them compatible with whatever format the end medium is to be, whether CD, DVD, reel tape or vinyl. Sequencing the tracks, applying corrective (or format) EQ, fades, gaps, fixes, indexing and final format storage that the reproduction facilities need. All that "recording studio gear" can get in the way of good mastering. Mastering requires very critical listening by a person with critical ears and sense of what is going on. Sure, there are "mastering" plug-ins for various DAW's but none are worth anything without the training of the mastering engineer. What is needed is an extremely good acoustic workspace and monitor loudspeakers that are very clean, accurate and very dynamic. The ME needs to hear the mix in great detail to be analytical about what changes need to be made. The success or failure of an album or CD can rest on his shoulders. A recording engineer is not the same as a mastering engineer, no matter what forum they write in.

      Since no hi-fi speaker, monitor or headphone is completely flat no matter the design, all loudspeakers color the sound to some extent. Monitors are assumed to be less colorful than typical hi-fi products since most consumer speakers are "colored by design". As we can measure the monitor speakers or components and build compensation for them, nothing really can be done to headphones to ensure they have a flat frequency and power response. The sound you hear from headphones is not directly comparable to the sound from a loudspeaker. You cannot gauge what your final output will sound like on different playback systems if you solely master using headphones.

      When selecting your audio components, choose the most transparent product you can. I can recommend the O2 wholeheartedly as I have built three of them already and am building four more for a project studio. They are far superior headphone amps than anything built into studio gear or PC interfaces I have heard. So many pro audio PC interfaces, especially ones sold for 'home studios/podcasting' are rather cheap overall and lack quality pre's and h.o.'s. For instance, Avid's top of the line MBox Pro ($1000) has a 33Ω output impedance.

  69. @Aaron Sheya:
    The XMOS Reference board you refer to is USB input only. The S/PDIF is output. There is stereo analog input/output and S/PDIF output via optical. The header is for debugging. Also, this design uses the CirrusLogic 4270 DAC chip. Just wanted to clarify that the board has USB input only, not an additional S/PDIF input. So, I guess in essence, all it is really is a USB DAC and/or USB-to-S/PDIF converter. Output is 1VRMS@0dBFS. Input is 2VRMS for 0dBFS output. It's ac-coupled output impedance falls with rising frequency 1kΩ@35Hz to 576Ω@1kHz and it's input impedance is 8kΩ. There is no headphone amp.

  70. @Aaron Sheya: Also, to compare them as pertains to the O2/ODA, the ODAC is USB In/Analog Out @2VRMS while the XMOS is only 1VRMS output. Plus, the ODAC is $50 less expensive so far. Cheers!

  71. I wanted to check back with you and also ask another question.

    I got my Cambridge Audio DacMagic and with the help of my daughter, did some blind testing between the DacMagic, Peachtree Nova, and Squeezebox Touch analog outs. Bottom line, I couldn't reliably tell the difference.

    I've sold the Nova and reinstalled my old Carver amp because the Nova didn't drive my speakers well at all. The touch is now plugged directly into my Carver via analog RCA cables and it sounds great with my Denon AH-D7000's

    Speaking of which...The Denons have a very low impedance of only 25 ohms, but I hear no evidence of any frequency response problems whether they are plugged into my iPod, Clip Zip, or old Carver (which I'm guessing has an old-school high 120 ohm output impedance). I've asked around and the only explanantion that seems to make sense is that the Denons, while being of low impedance, have a ruler flat impedance across the audible spectrum, so a high output impedance amp has little effect on them. Could this be so?

    Finally, you briefly touched on "$4000 power conditioners" and this reminded me of an "article" I recently read in the last Crutchfield Catalog I got in the mail. They sell the stuff, so I think I can assume a certain amount of bias, but they claim to have measured the "noise" of the electricity from the outlet and then from the sockets of several different power conditioners they sell. Of course, the wall outlet was very noisy, and the power conditioners were 10X "quieter." And again, of course, the more expensive the unit, the less noise was measured.

    I always assumed that the transformer inside the amp is what sent juice to the circuits, and the "quality" of the electricity coming from the socket was irrelevant - so long as it is of sufficient power and current. So, are power conditioners of all types truly just snake oil or is there some merit to feeding an amp "conditioned" electricity?

    Thanks again for investing your time to this blog!

    1. The Denons (at least the 2000) do not have ruler flat impedance but they're flatter than many. It's possible your Carver has a dedicated headphone output. It's also possible the differences would be more obvious in an immediate A/B test switching live between the sources.

      Crutchfield's new "labs" are, in my opinion, off to a very disappointing start. I was hoping they would do meaningful objective testing, but so far from what I've seen, they're not. They're either doing biased sighted listening or making questionable measurements such as power line noise. In my opinion their supposed "tests" are really more like infomercials. It's perhaps taking a page from what Jude does at Head-Fi.

      The proper way to measure a power line conditioner is to measure the audio performance of whatever is plugged into it vs the same device plugged into raw unconditioned power. The reality is most devices do a fine job of rejecting lots of power supply noise so adding a conditioner won't make any difference. The notable exception are single ended MOSFET/tube amps or other devices with low or zero feedback circuitry. But that's because those devices are poorly designed for their intended purpose in the first place.

      If you don't believe in measurements just set up two systems and run one from raw power, the other from the conditioner, and do a blind A/B comparison. Crutchfield could easily do such a test, but not surprisingly, they don't.

      If you can't hear power-line related noise, you don't need a power conditioner. If you can hear power-line related noise your money is probably be better spent finding the weak component and upgrading it rather than using a power conditioner as a bandage for some other problem.

  72. Dear NwAvGuy,

    Thank you for your talented work so far! I love how your Objective2 amp drives my LCD2 headphones portably!

    I will patiently wait for your future version of PORTABLE ODAC with S/PDIF inputs. I have read your "why no S/PDIF" arguments and can certainly understand.
    The following is my follow up comments, just for your consideration:

    1) I do not really care for O2 compatibility. As long as the entire rig is transportable and battery-powered, I am happy. O2 is not highly portable to begin with but I love its sound.

    2) IMHO, PORTABLE S/PDIF is still kind of a niche market. I am only aware of iBasso D10/D12, Fiio E17, HM-801 and a upcoming Leckerton UHA-6S MK2. That is all (I did not count Fiio D3 because even Fiio said
    D3 is NOT for audiophiles).

    The beauty of PORTABLE S/PDIF is that you potentially only need one DAC for all S/PDIF capable gears in your house, which include CD players, Squeeze box, PS3 and MP3 players (e.g., iRiver H1XX, Cowon D3/Q5W, Archos 605 w/ dock).

    3) Judging from the success of iBasso D10/D12 and Fiio E17, there is big demand for PORTABLE DAC accepting S/PDIF. I am sure many people will be willing to paying more than the current ODAC to get S/PDIF portably. Higher cost or being in another enclosure are not really major concerns, at least not for me. I would not spend a dime more on fancy cables, but for your ODAC, I would definitely pay more.

    Would you like to save our ears from Fiio E17 or iBasso D10/D12? Please do. Based on what I read, Fiio or iBasso do not provide that much of improvement to portable audio.

    Your O2 amp has raised the bar for portable audio; because of that reason I would rather wait for you portable S/PDIF ODAC than buying a Fiio E17. To my ears, O2 beats Mini3 for sure; I do not miss my AMB M^3 much, now that I have O2. And the portable O2 stands well against my Beta22 w/ Sigma22!

    1. Thanks for the feedback. You're not the first person to prefer the O2 over the M^3 and beta22. Several have done their own comparisons (a few even blind) and sold their AMB amps.

      I can understand the appeal of S/PDIF for home gear--especially something that might have a really cheap DAC in it. I also think it's important to be realistic. There are inherent advantages to NOT running digital audio over S/PDIF. The internal I2S interface is much less prone to jitter and does not require reconstructing the audio clock. This gives internal DACs a significant leg up on any external S/PDIF DAC.

      It's also important to note that without taking some rather extreme measures, that would be power hungry and impractical in a battery powered DAC, any S/PDIF DAC is at the mercy of the quality of S/PDIF signal you feed it. If the S/PDIF signal is laced with jitter, as it may well be coming from a battery powered portable player, the DAC's performance will still be limited. It's "garbage-in-garbage-out". That's one reason I like USB. You're not at the mercy of the audio chip in the PC/device.

      So my recommendation is if you have some device with a lousy DAC, upgrade the entire device rather than gluing on another DAC via S/PDIF. Where that doesn't work so well is a PC because the inside of PCs are so electrically noisy. But that's where USB beats S/PDIF.

      Such an upgrade might cost less than many spend on external DACs. Most of the Squeezebox players, for example, perform very well on their own. And the newer iPods are rather amazing as well.

      Just to be clear, the ODA will NOT be battery powered. It would be interesting to know how many have a genuine need for a battery powered DAC with an S/PDIF input? I say "genuine" because I suspect what many using battery powered DACs really want is an iPod dock digital interface which is not S/PDIF. I know there are a handful of rare portable players with S/PDIF outputs but that really seems like a niche to me.

      The fact is an iPod Touch already has a very nice DAC in it. The next generation will supposedly be even better and play 24 bit files. All you need, for headphones the iPod won't properly drive directly, is a decent headphone amp like the O2 running from the line output. No portable DAC is required.

      I suspect the portable headphone amp functionality is a more common use of the E17 (and the E7). I believe portable iPod DACs, like the iStreamer, are mostly a waste of money. If you have some old substandard iPod, you're better off getting a current iPod Touch for about the same price.

      FiiO products are popular because they're relatively inexpensive for what you get and have lots of nice features. iBasso products, as near as I can tell, are popular because they're heavily hyped and have a cult-like following of subjective evangelists on H-F. But, from what I've seen, they don't live up to their specs, have no solid measurements to back them up, and are based more on FOTM chips and snake oil rather than solid engineering.

      One of these days I'd love to put an iPod and O2 up against an ultra high end transport, DAC, and headphone amp in a blind test. I think the result would be shocking to a great many people. I really want to focus on helping solve real problems that will result in genuinely better sound. The biggest need was for a high performance reasonably priced headphone amp. A secondary need is to upgrade the rather marginal internal audio in many PCs and laptops with a USB headphone DAC. But I don't believe there are audible benefits to using an external DAC with say an iPod Touch 4G. If the DAC in your device sucks, get a better device.

    2. Thank you NwAvguy for your helpful advice.

      You have persuaded me. I will pass on the idea to get a portable S/PDIF DAC then. I do suspect that my iPhone 3GS' internal DAC to be pretty good, as I could not tell much difference when comparing it to some Aufio-GD DACs (which may not be so excclent to start with I guess). I would not even bet my money on it vs. my PreSonus Central Station or AMB Gamma2; I may be able to tell them apart sometimes, but doubt I can tell consistently with any music.

      In my experience, when a DAC is sufficient (I guess many current ones are), amplifier affects sound more, especially with hard-to-drive headphones.

      With regards to O2 vs. M^3 vs. Beta22, while I do prefer O2 over M^3 in view of its overall portability and sound, I prefer Beta22 over O2. Sorry I was not clear enough in my previous post. However, that is based my personal preference; I like that Beta22 provides a larger soundstage (you may call it coloration, though that is just my preference) than O2 with LCD2s. O2 is still amazing in view of its cost, sound and portability, of course.

  73. It's interesting your stance on current iPods dac quality. I pretty much concur but i disagree on your iBasso quote. I do have an iBasso T3 and to my ears it has a very low output impedance and has a clean and open sound. Thus for driving armatures it's hard for me to deem it as snake oil.Actually i think that it outperform a few bigger brothers.

    On a side note it would be amazing if at some point you are able to measure an iPhone 4 which might well be the most amazing portable source out there.

    It's a delight to read your blog. Keep it up

    1. I'm not saying iBasso may not have some reasonable products. But I know for a fact they've been caught exaggerating (to use a polite word) their already vague specifications.. And I don't agree with their design approach. They tout class A where you don't need class A, etc. They also crank out products way too fast to be sweating all the details, measurements, and proper engineering. As I've shown, product design is way more than throwing some trendy parts on a PC board and putting it all in a nice looking enclosure. But that seems to be the iBasso recipe. It took a couple engineers at Benchmark 2 years to design the first DAC1. How many products has iBasso released in the last 2 years? Doesn't one guy claim to design all their products? It doesn't add up.

  74. I just wanted to say thank you for all your hard work with the O2 and now the ODAC. I just received my O2 amp yesterday and i am glad to say that it is the best amp i have ever owned. I compared it to my cute beyond and the my Audio-GD C2C and i like it way better. It is nice to not have to crank up my volume just to get the channels matching.

    I haven't had that much time with it but i look forward to testing all my setups and music with it. Thanks to the stellar performance of this amp i am now an admirer of your work and cant wait to purchase and ODAC. I only have a nuforce icon mobile and look forward to upgrading.

    Upon discovering your blog i was disheartened to find that you had been ostracized from the head-fi community. From what i can tell you seem to be about promoting honesty. Well i for one appreciate your efforts as i have been misled in the past by what i have read on head-fi.

    Well just wanted to leave my 2 cents thanks for the good work and please keep it up. For the little guys like me who dont have thousands and thousands of dollars for cables etc

  75. Just wanted to say keep up the good work. I can't wait until this comes out :)

  76. I can understand your approach towards iBasso even i find it a bit generic. I still think though that the only iBasso product i've ever own (T3) it's quite good. If i was in the U.S. i'll be delighted to ship to you to take a listen (and may be a proper measurement). I'd bet you would be subjectively surprised.

    I can't help but encourage you again to put through test an iPhone since i find its headphone out a marvel of electrical engineering.

  77. I keep finding the O2 mentioned in the most unexpected of places: I was browsing a random music forum and noticed that someone has a photo of their O2 and headphones as their profile picture.

    After looking through the obligatory "Audio Headphone Stuffs" thread, it seems like there's a very strong bias towards the O2/Fiio gear, with plenty of links to this blog to boot. Couple of people getting all excited about the ODAC as well!

    It seems that outside the world of cognitivebiasophiles, your designs/measurements are really doing exceptionally well - but I don't think you need me to tell you that!

  78. Just put my last 15 dollars in my gas tank, still check the blog multiple times daily waiting for an odac, oda, or clip zip update. I'll have to take desperate measures to get my hands on the odac when it is dropped. Can't wait to get a listen to it.

  79. Hi,

    First of all thank you for your great input and devotion.

    I was going to start from "top" and buy really expensive set of headphones, amp and DAC. DAC itself was going to cost around 900€. However I just accidently got by your blog and started reading and reading and at the one point I was like NICE. No need to buy expensive gear just wait for ODAC :)

    Is it going to be possible from ODAC to control volume of active speakers? It would be really welcome option.

    Keep up good work!

  80. Hi I can't wait for the ODAC to be out and as I understand, the ODA will soon follow. Right now I'm using my O2 as a desktop amp rather than a portable amp so I'm interested in the ODA. Since I'm interested in both the ODAC and ODA, it makes sense for me to buy the ODAC+ODA in a single enclosure rather than buy both separately as standalone units. However I just have a concern:

    If i buy the ODAC+ODA unit, will i still have the ability to connect the ODAC to another amp (feeding the analog signal out from the ODAC to another external amp, bypassing the ODA entirely)? I predict that I might be using the ODAC with other amps as well so if I'm unable to do so with the ODAC+ODA unit, I'll have to buy them separately. Having an answer to this question will allow me to know whether to buy the ODAC once it's out or to wait till the ODA is out too.

  81. To answer the last two questions above in one post: With the ODAC you can control the volume in software on your PC. Or the ODA will have a preamp output and a volume control and can be connected to another amp or powered speakers (with the added bonus of a great headphone amp for headphone listening).

    Right now the plan is for the ODA to have a variable preamp output. But it may also have the option for a fixed line output for those who want to control the volume "downstream" of the ODA+ODAC. So it should be possible to buy (or build) the ODA+ODAC and use it both as a standalone headphone DAC and also to feed another music system or powered speakers.

    Finally, this article has exceeded 200 comments a few times and I've been forced to go back and delete comments to make room for new ones. I expected to have a new article published by now providing a new venue for comments. I may have to disable comments on this article soon. I should have the next article up within a few days.