Objective Reviews & Commentary - An Engineer's Perspective

October 5, 2011

Roadmap Update

innerfidelity_blog_NwAvGuyRecco_photo_main_300ARTICLE UPDATE: I’ve been publishing roughly one article a week but not always on the usual Wednesdays. Lately I’ve published and updated reference material for a guest article Tyll Hertsens asked me to write for InnerFidelity:

O2 UPDATE: There are a half dozen or so group buys around the world for the O2 in various flavors and forms. Much to my surprise, somewhere around 1000 circuit boards have been ordered making the O2 one of the most popular DIY headphone projects anyone can remember. That number is even more amazing when you consider most made their purchasing decision when there were only a couple O2 prototype amps in circulation. The boards have been ordered and there should be lots of people building the O2 in the next few weeks.

CHALLENGE UPDATE: I put out an open challenge to compare the O2 on a test bench or in blind listening to much more expensive headphone amps. I also threw out a challenge to hear the difference between op amps.  It’s been many months and not a single person has come forward. Where are all those who swear they hear obvious differences between gear or have been critical of the O2?

FUTURE ARTICLE POSSIBILITIES: There are only 11 more weeks left in the year and here are some possible articles (no promises) to wrap up 2011:

  • 4 Inexpensive USB DACs – Under $40 DACs as portable companions to the O2 amp.
  • FiiO E11 Review – How does it compare to the Mini3 it’s based on and the O2?
  • FiiO E6 Review – How does it compare as an upgrade to the E5?
  • Sansa Clip Zip Review – Sansa’s long awaited replacement for the Clip+.
  • Objective Desktop Amp (ODA) – The O2’s upgraded desktop sibling.
  • FiiO E10 Review – How does this upcoming 24/96 DAC/amp compare to the E7?
  • Flawed eBay Headphone DAC – Yet another typically flawed eBay design on my bench.
  • 24/96 USB DAC Reviews – I plan to test some other DACs capable of 24 bit USB audio.
  • Balanced Audio – The main advantages and disadvantages of balanced audio.
  • O2 vs DIY (Pimeta/JDS/AMB/Gilmore/?) – How does the O2/ODA stack up to other popular DIY amps besides the Mini3?

REVIEW DECISIONS: I get near daily requests to review some piece of gear someone already owns or is contemplating buying. Many are fairly obscure but there has been some consensus. Various inexpensive small USB DACs are the number one request. And the FiiO E6, E10, E11, and new Sansa Clip Zip, are also frequently requested. The E10 isn’t even widely available yet so it might not make it this year but the hopefully I can get the rest reviewed.

TECHNICAL TOPICS: There’s been a clear consensus for an article on balanced headphone gear but I’m open to suggestions for other technical topics. Are there suggestions for other technical articles with broad appeal I’ve not covered yet


  1. I have completely missed the fact that O2 boards are finally available. How do I order one?

  2. Perhaps I need to word it differently but I was trying to say around 1000 boards have been ordered as part of various group buys. Those group buys are now closed and awaiting delivery of the boards. Some have ordered extra boards and will likely be making them available in various ways (check the links in O2 Files & Resources). I also wouldn't be surprised if someone eventually stocks O2 boards or kits and sells them on eBay or in an online store.

  3. I'd be very interested in:

    1. Flawed eBay Headphone DAC – and also some other chinese "hifi" products/brands.

    2. Balanced Audio

    3. Inexpensive USB DACs

    4. Objective Desktop Amp (ODA)

  4. "somewhere around 1000 circuit boards have been ordered"

    Congratulations, I am thinking to replace my fiio e9 with o2, well need to find someone in europe to sell me one.

    I will love to read:

    1. 4 Inexpensive USB DACs – Under $40 DACs as portable companions to the O2 amp.

    2. Objective Desktop Amp (ODA) – The O2’s upgraded desktop sibling.

    BTW could I ask you kind sir one important question, I have AKG k702 (Impedance @ 1kHz: 62 ohms) and Fiio e9 (out. impedance 10 ohms), could you predict freq. response change of AKG becous of fiio? Is it -2dB on bass?

  5. Hi! If the following claims pique your interests (that may arise as a real contender since many swear by their xonar series)...

    Xonar Essence One
    World's first USB digital-to-analog converter with 8x symmetrical upsampling and 120dB SNR

    Output Signal-to-Noise Ratio (A-Weighted) (Front-out) :
    120 dB
    Output THD+N at 1kHz (Front-out) :
    0.000316 %(-110 dB)
    Frequency Response (-3dB, 24bit/192KHz input) :
    10 Hz to 48 KHz
    Output/Input Full-Scale Voltage :
    Balanced Output : 4 Vrms ( Vp-p)
    Unbalanced Output : 2 Vrms ( Vp-p)
    Headphone : 7 Vrms ( Vp-p)

  6. I don't know the impedance curve of the K702 (how the impedance changes with frequency). But it's probably not worse than 120 ohms at the bass resonance. That would be less than 1 dB of error using the 1/4" jack on the E9.

    I'm less certain about the effect on the bass damping but you're probably OK there as well as it's close to meeting the 1/8 rule. Unless you want a portable amp, the E9 probably does OK with the AKG's.

  7. @NwAvGuy: Thank you for your replay.

    Impedance of AKG k701/2 vs Freq:

    Yes AKG is ok with Fiio, but not with my 16-32 ohm headphones. So o2 is cheap answer, allrounder.

  8. K702 impedance X frequency

  9. Congrats on the Innerfidelity article. Dunno why, but I'm kinda happy that your opinions are valued by a guy as respected as Tyell.

  10. According to Tyll's measurements, it's like 72 ohms in the bass, and still below 100 at 20kHz.

    As for suggestions, I don't really know because I'm pretty much intrested in anything. Maybe something about headphone measurements, that wasn't mentioned yet.

  11. Thanks everyone for the comments. As for the blatant plug for the Essence One does anyone know the price in the USA yet? If it's around $400 or more it will have some significant competition like the replacement coming from Emotiva for the XDA-1. If it's under $400 it might be a worth trying to get on the test bench. I like that it supposedly comes with Audio Precision test data but claims like "8X Symmetrical Upsampling" are mostly just marketing hype.

  12. Small and cheap are always good topics, so I'm onboard with the FiiO E6.

    So here's something interesting. I was part of a discussion on balanced (differential) versus traditional single-ended headphones and brought up a chart from HeadRoom's Learning Center showing that the balanced headphones showed MORE distortion than single-ended. Everyone immediately lost interest but me because I figured the differences were negligable and I think you can get up to another 6dB of channel seperation... and that is interesting to me.

  13. @akgk171, I'm not sure what you're asking? You can get far more than 6 dB of added channel separation with a 4 wire headphone connection, but that has nothing to do with balanced amps. In general, balanced amps have MORE distortion, MORE noise, and WORSE (double) output impedance. Those negatives are significant and hard to avoid.

  14. The Asus Xonar One (http://www.asus.com/Multimedia/Audio_Cards/Xonar_Essence_One/) should come bundled with a test report from a Audio Precision SYS2722 system. I'd trust Asus's listed specs.

  15. Anon, I already mentioned the AP measurements. I'm not questioning the specs, I'm questioning the PRICE. What will the Essence One sell for in the USA? If it's more than $400 US there are likely better options.

    I'm not likely to approve posts with more links to Asus as your posts seem to have a commercial interest. This is a non-commercial blog.

  16. Ah I missed that comment. I'd like to clarify that I don't have any commercial interest with Asus other than that they might get my money. The link's just to show that it will come with one. Apologies

  17. Please include the Fiio D3 in your inexpensive DAC roundup. its <$30 and I am considering it as a partner to the O2.

    Also if there are any inexpensive DIY dac's that measure well id love to take a crack at one, but I do understand why this is an area where economies of scale are hard to beat.

    Other than that, cant wait for the ODA!

    On a side note, have you noticed that Steve Guttenberg is now doing guest articles on head-fi-- right after publishing his article on how on how sound quality is immeasurable? I rolled my eyes pretty hard at that. Birds of a feather I guess.

  18. nwavguy, i think it would be great if you could measure the fiio e10 soon.. based on initial info and early review (from review samples), it seems that it's going to be a small desktop version of e7 that measures well (based on your previous measurements), and having the power output of e11.. i believe many people would be interested in it, a cheap DAC/amp combo that measures well, hmm..

  19. As I have already pointed out in private correspondence, the Asus Xonar Essence One retails for about 18000 TWD, according to the following thread: http://my-hiend.com/vbb/showthread.php?t=1672&page=169
    This is currently about 585 USD and I would be very surprised if it retailed for significantly lower than that in the US.

  20. Forgot to mention: I also expect the Asus Xonar U3 to measure worse than the Behringer UCA202, as it's probably some cheap integrated C-Media solution.

  21. I'd be looking forward to the ODA - I never saw the point of a portable amplifier. To me a portable music system should be first and foremost portable.

  22. I'd be very interested in the ODA. Is there a possibility that it will be designed to house a DAC (USB or optical) in addition to the amp? Do you have plans to design a DAC?

  23. Thanks for all the added comments. If the Essence One will be close to $600 it's going to have some significant competition from several dedicated audio companies.

    @Inarc, based on what I've seen so far you're probably correct about the U3. The integrated C-Media chips, like the CM119, have some serious problems.

    @Mikey G, I will be testing the FiiO D5 as it offers USB. The D3 lacks USB severely limiting its use--especially with laptops.

    As for Steve G, he should be careful. Celebrities make ideal candidates for public blind listening challenges. :)

    As for the ODA and a DAC, no promises, but I'm working on just that. :)

  24. @NwAvGuy Optical In is very useful for things like TV and Macbook Pro owners ;) And I actually like that it would use optical, not USB. But, I'd assume that the DAC's and performance for the D3 and the D5 would be very similar. Also, the D3 functions as a "no frills" DAC with line out.

  25. headphone cables/interlinks.
    Would be nice to get that sorted on here as well.
    Much too persistant.
    tubes (valves) also a topic.

    how audio is converted/strored digital)/converted again.

  26. I'm fairly sure you don't need to waste time doing a Clip Zip review, it's the same AMS SoC used in the Clip+ and Fuze. It should have the same, or nearly identical performance.

    I'd be interested in a Balanced Audio post, because I know almost nothing about it, tbh. ;)

  27. Wow so good you have posted what you are thinking of doing the rest of the year! Almost all of it is very interesting IMO.
    The things I'm interested in the most are:
    1. 4 Inexpensive USB DACs – Under $40 DACs as portable companions to the O2 amp.
    2. FiiO E10 Review
    3. O2 vs DIY
    4. O2 vs E11

    And obviously the Objective Desktop Amp (ODA)...

    If there was an award for Shaking the Audiophile Tree I would most definitely nominate you!

  28. I'd be more interested in reviews and tests of higher-quality DACs.
    Of course it would be great to find a low-priced DAC that measures well on your test run.
    But somehow my hopes on that are close to cease existing.

    Units like the AckoDAC and the Buffalo III seem more interesting.
    Short, anything that has a chance of matching the sonic quality of the O2.

    And I really hope my O2s turn out as good as I imagine them according to your measurements.

    Other topics of special interest to me: ODA, O2 vs other DIY, PC soundcard measurements.
    The last point is of interest, because 99% of the USB-connected DACs dont have BluRay licenses and may be great for music, but disqualify them as one-size-fits-all.
    And the Asus Xonar HDAV 1.3 in my rig "sounds great" but I lack the skill and equipment to do measurements myself.

    But whatever you decide on: This blog has been a great read so far.
    I've even printed the articles and once theres enough of them, I'll have them bound to a book, because they are distilled to the essence and a good starting point for further research and learning.

  29. I'm voting for the articles about balanced audio and the upcoming E10 - Thanks! :)

    I haven't purchased any O2-DIY-hardware so far, since I mostly suck at that sort of stuff, but I've preordered one at Epiphany Acustics (in UK) .. still no response so far though, on when they might start producing them. Epiphany Acustics is the only "official" manufacturer in Europe right? (Since they're the only ones you mention on your blog)

    Also one last question, because you mentioned "only 11 more weeks this year", does this mean you'll discontinue your blog next year?

  30. It's been quite a while since I first started reading this blog. Very interesting, fairly easy to grasp and always relevant articles. Audio blogs like this are few and far in between.

    I've been posting some links to your articles on the heavily-funded forum. Recently I got banned from posting there.

    My intentions were good. I wasn't trying to start a flame war or anything. Was merely trying to warn the guy against opamp rolling. That guy was grateful for the article but I guess the admins found that post and decided that I was posting on behalf of banned persons.

    They didn't contact me with a reason for the ban though. I just got shut out. lol

    Meh. It's a shame. I get the feeling they want to keep everyone in their own big Headfi bubble of pseudosciencecrap. Any attempt to bring members back to reality = instaban.


    Not blaming you for anything though. I have since started my own subjective audio blog to pen down my thought, I write about movies, audio, headphones, etc.

  31. Thanks again for all the added comments and suggestions (which kind of got backed up for approval).

    @GuiltySpark, I have no plans to end this blog, I was just mapping out some possibilities before year end. MrSlim and Epiphany are currently the only sources I know of for a completed O2 but I suspect there will be others in the future.

    @Johnny Bravo, sorry about the Head-Fi ban. Several others have been banned there in the last month or so for mentioning me. Their policies seem as unpredictable as ever. What's allowed last week by one member results in a ban of a different member this week.

    The more Head-Fi tries to suppress factual information helpful to the majority of their membership, the more they're encouraging people to take their contributions and page views elsewhere. InnerFidelity is an example of a site with similar commercial sponsors but a far more rational policy regarding content. Tyll welcomed my article there while Jude banned me at Head-Fi. It's obvious they have very different agendas. I think many more are growing suspicious of Head-Fi and seeing the site as a giant infomercial.

  32. Well thanks for the contributions, as always.

    Personally I'm most interested in cheaper USB DACs, both for myself and as a reference to recommend to others.

    re: heavily-funded forums

    For some reason I'm getting an urge to post a link to the InnerFidelity article in a relevant discussion and see what happens there. ;)

  33. "As for Steve G, he should be careful. Celebrities make ideal candidates for public blind listening challenges. :)"

    Now, now, be gentle.

    Inarc, the Asus Xonar U3 is a proprietary Asus chipset whereas the Essence one is a C-Media CM6631.

  34. Thanks SpaceTimeMorph. I still may test a U3 someday. There's also the new cheap HiFiMan USB DAC. In the testing I've done so far, the C-Media CM119 has a low output impedance and can manage more output than a lot of portable players. But the DAC and other audio performance is fairly poor. It's sort of the opposite of the Behringer UCA202 which has semi-respectable audio performance but a really lousy headphone output.

  35. SpaceTimeMorph wrote:
    "Inarc, the Asus Xonar U3 is a proprietary Asus chipset whereas the Essence one is a C-Media CM6631."

    I am fairly certain that Asus' UA100 is a rebranded, possibly custom-built C-Media chip. As for the Essence One, the CM6631 is just an USB controller, not a wholly integrated one-chip solution.

  36. ^ Doesn't matter about output impedance I think... I'd just connect it to an O2 anyway ;).

  37. Will the ODA be ready before winter starts?
    I rather not solder things in the cold.

  38. O2 vs. DIY! Would love to see comparisons :)

  39. (second choice: 24/96 USB DAC Reviews, would love those, too!)

  40. There's no way a $40 Dac will sound as good as the Emu 0204, even though I'm angry at Creative's ASIO drivers. So I don't have much interest in cheapo Dacs. Seems like a bad idea pairing a $120 headphone amp to a Dac that costs a third of that. No way the O2 will sound its best. 0204 + O2 will have to do the trick for me. I just can't surf the web when I'm using ASIO unless I can stand glitches. The Fiio E6 is far more interesting to me as the O2 cannot replace super portable amps and the E5 did not perform up to the level that made it worth buying for something like Clips or iPods. E6 could be a major leap for people.

  41. Thanks to all for the added input and comments.

    @inarc (or anyone else), Do you know if the Essence uses the same USB chip as the Schiit Bifrost?

    @Reticuli, in theory a $40 USB DAC mass produced in China designed for function over form (i.e. not in a fancy chassis, etc.) can perform well enough to be audibly transparent. I'm not saying such a DAC exists but the UCA202 comes very close. If you take all the recording hardware, mic-preamps, level controls, peak/clip indicators, extra connectors, etc. out of the E-Mu 0202, and put it in a smaller/cheaper enclosure, it could probably sell for around $40 street price.

    @anons, I will be testing the E6 and hope to have at least an initial ODA article published before December but no promises. It's much less likely a PCB group buy will be completed with boards delivered this year. So those wanting to build one will be soldering this winter. It's a good indoor activity ;)

  42. NwAvGuy wrote:
    "Do you know if the Essence uses the same USB chip as the Schiit Bifrost?"

    Google says yes, but what do I know?!

  43. If you choose to do the DAC topic(s), could you maybe do a round-up or side-by-side comparison of them?

    While I really love your articles and the detailed information they provide, it makes comparing the products harder for someone who doesn't know exactly what he's looking at.
    I've tried comparing the graphs with each other, but it's a little tiresome given different scales and so on - and in the end I'm not quite sure if what I did was correct anyways.
    Case in point I'm still not sure wether the E7 or the UCA202 is the better choice for DAC-only desktop usage...

    Thus it would be great if, additionally to the graphs, you could maybe sum up the relevant measurements in tables. :)

  44. Thanks Inarc, and GuiltySpark I do summarize the measurements in a table in all my later reviews including the E7 (but not the UCA202). My article at InnerFidelity helps explain the measurements and what to look for. Unfortunately, what's "better" often isn't black and white. One DAC, for example, might have lower distortion but higher noise than another.

    My review strategy is still a work in progress and I appreciate the feedback. I am trying to further standardize my measurements and make it easier to compare products among not just my reviews, but those being done by others such as Tyll at InnerFidelity.

    As for DACs, if you're not in a huge hurry, I'll have some more DAC reviews up shortly. And, based on preliminary info I've seen elsewhere, the new E10 is probably a better choice than the E7.

  45. Lovin' the articles!!

    I purchased a board and a front panel from the diyaudio group buys and I can;t wait to build it!!

    I've never had a headphone amp before so hopefully this will be a good one!

    I am also very interested in inexpensive USB DAC's as I am a high school student and don't have much money and I frequently use my laptop to listen to music via Spotify or MOG.

    The Clip Zip has also sparked my interest as I currently have the Clip+ and loving it! Still gotta Rockbox it though...


  46. I believe those who ordered the O2 might have the misconception that pairing a clean O2 amp with under $40 DAC (even though it might be "good enough") is doing O2 injustice. That's human (and i'm one of them)! But i am glad that you'll filling that gap with 24/96 USB DAC reviews! Maybe a suggestion is also to recommend one companion USB DAC that has reached the diminishing returns (for different segment of readers with deeper pockets).

  47. NwAvGuy: "In the testing I've done so far, the C-Media CM119 has a low output impedance and can manage more output than a lot of portable players. But the DAC and other audio performance is fairly poor."

    Sounds about right for a CMedia device. The digital parts tend to work pretty well, but their converters have always been very basic affairs - no doubt in order to keep cost down. Remember the "classic" CMI8738 didn't even have an A/D antialias filter... There are a few "audiophile" cards based on the CMI8770 around, with nice build quality, socketed opamps and all - basically a waste.

    Otherwise, very interested in the ODA, and not all that much in the Clip Zip (as mentioned, it should perform about the same as a Clip+).
    Re: balanced audio, I found Douglas Self's "Small-signal audio design" book a fairly good read, specifically the line input chapter.

  48. The few I'd be interested in are the cheap USB DACs, the ODA, and the balanced article in that order.

  49. Do you think it might be possible to develop some kind of non-instrumented tests for some of the various factors that you measure with your expensive equipment? This may seem self-evidently a non-sequitur in view of 'objectiveness' however perhaps there are ways of manifesting clearly audible artifacts that might be useful as a "finger in the air test" that would be an improvement on the usual subjective opinions. I often find that considered reflection and ingenuity can solve, or much improve, upon seemingly impossible problems. With so much kit out there - and headphones - we are prey to a lot of rubbish (and subsequent disappointment) that I don't expect will ever be truly addressed unless your kind of testing becomes a legal requirement for a review (which I am ideologically against, in any case).

  50. Thank you for all of your work, I check your blog religiously :)

    I would be interested in your opinions on various amplifier output topologies, especially the digital ones; Lab Gruppen has Class TD, Crown has Class I, Yamaha has EEE (or something like that) etc, I realize that these are all types of PWM driven outputs, but I would be interested to hear your opinions on the various methods used, which you think are best etc.

    Also, various methods of sound transduction (balanced armature vs. typical diaphram) would be interesting - speaking of course about headphone transducers here :) - I do not know if you have 'reference microphones' or the sort of equipment to do analog measurements but that also would be cool.

    Thanks again!

  51. Thanks all for the added feedback and comments.

    @Stephen, Self's latest books are all excellent. What's surprising to me is how many DIY and commercial designers seem to either be unaware of his proven research or they choose to ignore it and their designs suffer as a result.

    @Chesteta My opinion on "switched" amplifiers is they're a compromise. A proper linear conventional amplifier can always outperform the various switched technologies. But switching amps still have their place--especially where you need a lot of power in small package, the most power from a limited power supply, and/or the most power with the least heat. They're especially well suited for portable audio, pro sound, car audio, small multi-channel AV systems, powered speakers, and subwoofers.

    I'm not current with all the latest topologies but I know some haven't worked out very well. Several A/V receiver manufactures, for example, have gone back to conventional output stages. I have a lot of respect for the Hypex amps by Bruno Putzeys in the Netherlands. He seems to have done better than most at overcoming the typical problems with switching designs.

    The "keeping the entire signal path digital" argument is usually pure marketing nonsense. The D/A process has to happen somewhere in any signal chain and it's arguably easier to do properly before the power amp.

  52. For those of you who are saying that a cheap DAC will not be good enough - I highly doubt it. I think you are overestimating the importance of the DAC in the audio chain. Both the amp and headphones are more important in my limited experience. I have the Music Streamer II (24/96 DAC) but I'm very interested to see if cheap (well measuring) DAC's can compare. I'll wait to see if an Objective desktop DAC/AMP comes into existence though.

    I'm interested in. . . pretty much everything. :) esp. balanced amps and the ODA


  53. Just about comparing measurements:

    I really liked the tables you drew up in a couple of your reviews and also love them for camera comparisons etc.
    Key data next to each other allowing for easy comparison.

    BUT: all the sites that used them were "dynamic" sites, I.e. Php or asp.net and thus generated comparisons on the fly or contained all the info available.

    Creating these tables by hand is tiresome - unless you have a template to expand that you can then post. I personally would really suggest something like a mysql based database and php that will allow the reader to pull up a comparison, but it don't think google blogger can offer this.
    I don't know whether wordpress can either...
    Dedicated hosting could, but it would cost you money to run, which is really too much to ask. Also, someone would have to write the site. (while I know some php I know little about securing a php site)

    Alternatively, naybe you know someone who can give you a bit of server space to host a comparison database with your measurements?
    (sorry about any typos)

  54. I'm voting for

    Objective Desktop Amp (ODA) – The O2’s upgraded desktop sibling.


    24/96 USB DAC Reviews – I plan to test some other DACs capable of 24 bit USB audio.

    There's some good info here on inexpensive headphone amps, but I don't think I'm alone in having a little bit more to spend (say few hundred) on quality audio, am pretty interested in desktop audio and my sources are USB or SPDIF. However, a Benchmark DAC is a bit on the pricy side :-)

    Anyway, thanks for a good blog, I'm a SW engineer but enjoy a read on EE sometimes :-)

  55. @Satellite the MS II is an example of a great reasonably priced DAC. If you want 24 bit support you currently have to spend a bit more but that will hopefully change.

    @DetLevCM dynamic comparison tables would be great but this blog, and all the behind the scenes testing/designing/etc, already takes more time than I'd like. Something like that is more likely to happen at a commercial site like InnerFidelity.

  56. I would be very interested in E10 review. E7 is clunky to use with its buttons, I'd much prefer a wheel, if SQ is on par.

  57. E10, D5 and other low cost 96/24 USB DACs (there are not too many of them for all I know)

  58. The E10 can supposedly do 24/96 over USB, the D5 cannot. The D5 is 16/44 over USB using an integrated C-Media chip. I have a D5 and I'm not very impressed so far but it's cheap and has some features other DACs in the same price range lack.

  59. Regarding USB DACs -
    It would be great if you could take a look at the HRT Head Streamer when it comes out, if the price is reasonable.
    Seeing as the MS II is a great DAC, I am very hopeful about it (and hopefully it will only be in the next price bracket from the likes of the E10).

  60. Fantastic blog/site. Great to see some engineering objectivity applied to audio, and thanks for sharing your wealth of knowledge.

    Most interest for me - USB DAC/amps. Was curious about the "AudioGD Sparrow" or similar?

    I've Senn HD-565 Ovations and HD-595. Currently just running direct from PC, and the board connector is failing... good excuse to buy an amp.

  61. @SpacePixie, I hope to test the new HRT.

    @Anon, If someone wants to loan me an AudioGD product someday I might test it. But from what I've seen, most of their products are "designed by ear" and measure rather poorly--sometimes horribly. Anything with their discrete op amps, for example, will have hundreds of times more distortion than even an iPod.

  62. I possibly sound a bit like a broken record on this, but if we are down to wishlists...

    I'd really love to see one of the ProJect Boxes tested - but considering they use RCA to interconnect, they end up being a bit of a "closed system" if you want small equipment and don't want to roll out standard hi-fi gear.

    Maybe some day I'll see that review :)

  63. I believe the one ProJect product I looked into uses a capacitor coupled headphone output. That's far from ideal. Their higher-end products might be better but they have lots of competition at their price. Although I think they're proportionately cheaper in Europe than they are here in the USA (compared to say USA amps). But still, I'd probably suggest spending a few more Euro's for a Violectric over the high-end ProJect.

  64. Yes, we talked about it - specifically a headbox II amplifier.

    The question about the DACs remains though.

    At the same time a Violectric system wit a DAC is about 3 to 4 times more expensive - depending on the (USB) DAC you chose, headbox II + DAC = 200 or 250€
    Violectric starts at 450€ without a DAC. If you want the DAC as well you need a higher model with a combined price of at least 750€ (-5% on web order)
    If you take the higher end usb DAC it is 800€...

    So while they make significantly better equipment, it reflects in the prize.
    So for people getting into audio or on a limited budget the violectric stuff is more something to aspire to. Fiio is more of a direct competitor to the Project stuff if ordered on Amazon with a similar price tag.

  65. You may want to check out a $4 USB sound card which uses the CM119 chip. I bought one off eBay recently to fix the hum noise from the mic-in on my laptop and found it to quite good.

    It's call Music Fairy and supposedly it has one of the "better" USB chips made by CMedia, compared to the generic $2 alternatives. I was about to buy Behringer's USB interface or Creative's Sound Blaster Play! USB dongle for $20-30, but then I went for the even cheaper route and surprised myself.

    You can use this as a low anchor for your DAC comparison, like the codec/audio compression listening tests.

  66. @kingpage, Thanks. I have a Syba CM119 USB DAC already and will be including it in the upcoming reviews.

  67. That's good to know.

    I wonder if you will release a schematic without the extra space for batteries making it more compact. If you make a desktop version, are you to go make it bigger to further improve the SQ or will it be smaller? The battery slots make up 1/3 of the space of the board. For those of us who only use it at home, it is a waste.

    Of course, the reason I asked is that I have very cool looking amp enclosure that is 79mm*61mm*36mm which is a tad smaller than what is needed. Is there a easier way for us to transform your schematic easily with the help of a program or something? I just think if batteries are not included, I could make it fit into my existing desktop amp.

    Thanks for you contribution. I look forward to what you have in store for us in the coming months.

  68. @kingpage, Because the upcoming desktop amp has several upgrades, and is not designed to be portable, the board will be at least as large as the O2 (100mm x 80mm) and might be larger. If you wanted to use your enclosure you would need to do your own custom layout of the O2 without batteries. Expresspcb.com and others offer free board design software.

  69. Hi, NwAvGuy!
    First of all I'd like to say it's nice to see an island of objectivity in this vast ocean of audiophool* madness.
    Quite an interesting and (most importantly) informative blog you have there.
    As for (possibly) upcoming articles, I'm most interested in "Balanced Audio", "ODA", and "24/96 USB DAC Reviews".
    Speaking of DACs: in my quest for a decent USB DAC for my laptop I recently stumbled across Halide Design's website. These guys, among other stuff, offer two USB DACs: "devilsound DAC" and "DAC HD". According to Halide, their DACs features asynchronous USB technology, plug-and-play Streamlength driver etc.
    There aren't much info on these on the Internet so I was wondering if it's possible for you to review some of these DACs. They aren't the cheapest, though ($350 for "ds" and $550 for "HD"); but the latter is capable of 24/96 audio, so you probably may be interested in reviewing it.

    BTW, you once mentioned that you have heard some of the STAX earspeakers. Many of head-fiers consider these to be the "Holy Grail"
    of the headphone world. So it would be nice if you post some impressions.

    Best regards.

    * Audiophool (not to be confused with "audiophile")
    (US) IPA: /ˌɔː.di.əʊˈfuːl/
    audiophool (plural audiophools)
    1. (pejorative) Snake oil audio believer in general.
    2. (pejorative, rare) Head-fi adept.

    P.S.: "Damn, Blogspot doesn't allow for correct IPA copypastaing."

  70. Further possible 16-bit USB DAC: http://www.headfonia.com/hifiman-express-hm-101/
    (Ignore the woo.)

  71. what is the components + pcb cost limit you are aiming on your ODA -considering it has a dac-?

    just my opinion, but in case you want some annonimous feeedback....dont be afraid of reaching $250 or even more, there is a serious lack of quality "computer stations" diy projects and i think the kind of people who will build your designs understand that quality -most times- has a cost and probably are willing to invest in it.

    keep up the good work

  72. Hi,

    First of all, thanks for this great blog full of great information! I really appreciate the objective presentation of your articles. Are you considering testing the Yulong U100?


  73. @hlin599, the "flawed eBay headphone DAC" I plan to review is similar to a Yulong U100. I've had really bad luck with the eBay DACs.

  74. Thanks for the quick reply, looking forward to your review :)

  75. Perhaps you can try reviewing the Audinst HUD-MX1, given how much it's recommended as THE budget DAC.

  76. As a teenager I used to buy all the Hi-Fi magazines every month, lusting after all the delicious gear. In my early 20's I was fortunate enough to be able to afford to buy some of it. I quickly found that despite the reviews I couldn't really hear that much difference between item A and item B. But what really put me off was the very poor build quality of most of these A rated products, as well as the increasingly ridiculous and absurd snake oil being peddled. What I really wanted was to listen to music, not have to babysit and molly coddle expensive Hi-Fi components or have to read rubbish about how bits of foil stuck on walls magically improves the sound.

    So I started again. I restricted my purchases to highly rated (but not mega-priced) and properly bench tested items from major manufacturers who wouldn't go out of business in 5 years time, were highly respected and used sound scientific principles in their designs. And I made all my own interconnects using pro standard ofc instrument cable.

    25 years later I am still using the same items (servicing and upgrading the caps etc as needed) and adding new technology items using the same criteria as 25 years ago. Without exception, everyone who comes listening to my system is blown away by the sound quality. And the money I have saved in hardware has of course bought me lots of lovely music to listen to. After all, isn't that the whole point of this crazy hobby - listening to music?

    As a musicphile, I rarely visit the 'audiophile' forums, except for a laugh and to keep up with what's happening in the crazy schizophrenic world of Hi-Fi. Whenever I do post my views on forums, they are often met with derision and anger. For example, on one pro audio forum I once complained about the increasing rarity of well recorded music and that the most important piece of recording equipment was ones ears, and the most important upgrade was to go see an audiologist. You can imagine the response I got . . .

    Anyway, long story short, by chance a link I clicked on a link led to your blog. What a breath of fresh air you are! Definitely someone this 'hobby' has needed for a long while. And by the number of positive comments you are getting, I am obviously not alone in thinking this. . .

    By designing the O2, and seeing the overwhelming positive response it has generated, you have shown to your detractors that you do know what you're talking about, even if you won't tell us who you are!

    I do agree with almost all you write, especially your views on the objective Vs subjective debate. Personally I hate reading reviews where they spend pages describing in intricate detail how something sounds and then don't bother to actually measure it! To me something either sounds bad, good, better or worse than something else, or excellent. End of. Everyone with half a working brain cell knows that most of the time manufacturers specs are probably optimistic, are there to look good, and don't necessarily reflect real world usage. As you have shown, a perfect example is a certain AMB product, powered by an amazing battery, with only one channel driven to full volume. Realism or fantasy?

    Although I appreciate that your main area of interest is in portable audio, many of us also have home systems and I would greatly appreciate it if you could consider giving us your thoughts on pre and power amplifiers. Reviews of excellently designed value for money amplifiers would also be greatly appreciated.

    I have signed up to one of the forums you recommended and will continue to follow your blog very closely.

    Keep up the good work!

  77. Edit: What I meant by 'should see an audiologist' is that in quite a few recordings I have (LP as well as CD), the sound balance is inversely proportional to the recoding engineers hearing loss. In others the overall sound is (sorry for these subjective terms), muddy, closed in, lack of soundstage etc. I'm not talking about the loudness wars here, that's another huge kettle of fish!

  78. @Anon, thanks for the praise and comments. Recording engineers also are biased by their personal preferences and those of whoever hired them. The world has really changed as you don't need a million dollars worth of hardware to record and mix music anymore. You can do all the mixing and engineering in your bedroom with an almost endless pallet of creative options. So the results these days are more variable than ever.

  79. I feel like the 4 Inexpensive USB DACs – Under $40 DACs as portable companions to the O2 amp would help me out and many others as well. There are just too many to pick from...

  80. I vote for:
    FiiO E10 Review
    Objective Desktop Amp (ODA)

    Your whole blog is amazing, I love your logical and objective approach to the world of audiophiles.

    A question- I recently picked up a Fiio e10 and Sennheiser HD650s. The Fiio e10 has a bass boost function on it that I really don't see on other DACS/Amps often, and I am very seduced by it and decided to just leave it on all the time as it is pleasing to my ears.

    All I could find out about this function is from fiio's website: "Bass boost,OFF:0dB;ON:+3dB , built-in bass boosting circuit ,it’s different with traditional software to set the EQ, the effect of E10 will be better."

    I can't tell if that is marketing BS or not. I also don't know if I like the bass boost because the Fiio e10 can't drive hd650s enough or that is false. I would like to upgrade to your O2 desktop Amp/DAC when it is released, can I somehow simulate the bass boost with software EQ or do I really need a AMP with bass boost to get correct bass boost?


  81. @StarBeamAlpha, You can generally, with the right EQ software/feature/tool, perform the same EQ in the digital domain as the FiiO is doing in the analog domain but there's a catch. To avoid digital clipping, digital EQ can only safely boost frequencies by lowering everything else. With a 24 bit DAC and a low noise floor that's not a big deal. But with a 16 bit USB DAC, and/or a higher noise floor, it may slightly degrade the sound quality. So FiiO's claim has at least some truth behind it.

    The E10, based on what I've seen, might be marginal for the HD650 in terms of output level depending on how loud and what kinds of music you like. The amp puts out the same amount of maximum power with or without the EQ. With the EQ on, it's more likely to clip on bass frequencies. But if it plays loud enough for your tastes, and sounds good, that's what matters most. I'll be testing the E10 when they're more readily available in the USA.

  82. Thanks for the enlightening info. I'll stick with the e10 for now, and pickup an O2+DAC when the diy crews start building it.

  83. Any plans on designing an O2 DAC based on the same principles as the O2 amp?

  84. @StarBeamAlpha, you're welcome.

    @Anon, As I mentioned earlier in the comments above, the current plan involves a DAC option for the upcoming desktop version of the O2 amp but it's still in the early stages. The present plan is the DAC could also be used standalone and it will support true 24/96 over USB--something very few DIY DACs can do. Unlike all DIY DACs I know of, the performance will be thoroughly documented on professional instrumentation.

  85. O2 desktop with DAC sounds excellent, I was thinking of getting an O2 from Epiphany here in the UK but am in no hurry so will wait to see what happens with that in the future.

    If the O2 measures very close to as well as the DAC-1 as an amp, is it too much to hope you'll be able to manage the close performance to the DAC-1 for the DAC as well?

    Also, a little off-topic but you mentioned about the problems of the 3.5mm TRS jack in the O2 measurements thread and the improvement a "four wire" system would use, what do you mean? Do you mean the perfect hp amp might be single ended inside but use an XLR or TRRS plug? Or have I (likely) completely missed your point?

    Keep up the good work anyway, I really enjoy your blog.


  86. @Anon, if you're asking if I'm expecting Benchmark DAC1 Pre performance for a tiny fraction of the price, that's a loaded question. In terms of overall measured performance I seriously doubt it. The O2 can't match the DAC1's headphone voltage and current output and I doubt an inexpensive DAC will match the DAC1's D/A performance--especially for jitter as the DAC1 uses an elaborate (and expensive) ASRC, custom FPGA, and licensed technology from Centrance. The DAC1 also has several man years of development and refinement behind it and keeping the price down wasn't a major design goal.

    It's a different question to ask if a ODA/DAC combo can hold its own in a blind listening test against the DAC1. With 95% of the headphones people are likely to use I believe it's at least possible but I won't know until I (and perhaps others) try.

    The 3-wire vs 4-wire issue is purely one of crosstalk from the shared ground connection. It's likely only an issue with very low impedance (i.e. around 16 ohm) headphones and even then I'm not sure it's audible. But you can certainly measure a significant difference in crosstalk.

    And yes I believe conventional single-ended amps are best for headphone use with a 3 or 4 wire connection. The only possible exception is with a single voltage power supply and you're willing to use a 4 wire headphone connection. In that circumstance a properly designed balanced/bridged amp would likely perform better than trying to use a virtual ground or capacitor coupled outputs.

  87. Did anything come from that talk about testing any of the Twisted Pear DACs that was mentioned somewhere in the O2 thread on diyAudio?

  88. @maverick, the Twisted Pear thing never went anywhere. I'm less interested now as hopefully the ODA DAC will be smaller, cheaper, simpler and offer true 24/96 (and 24/44) over USB with point-of-diminishing-returns level performance. If that works out, I see little reason to buy any of the Peachtree DACs (although I can understand those who own one wondering how well it really performs).

  89. I'll look forward to the ODA DAC then.

    Is it going to be that Violectric DAC module or are you keeping it under wraps for now.

  90. It's not the Violectric module but the current plan is somewhat similar. The Violectric solution is a bit expensive for what it is--especially for those outside Europe. The folks at Violectric have been interested and helpful so that could still be an option if the current solution doesn't work out for some reason.

  91. about the ODA amp, ..will it be based on the national buffers or will it be opamp as the o2? either way i will be getting one, but i am curious after seeing the wire measurements over diyaudio, those pieces look well worth the money

  92. @Anon, it's (so far) a well kept secret :) But, regardless, I'll gladly put the O2 and ODA up against The Wire in a blind listening challenge with any of the 98% of current headphones that are within the O2's output capability.

    I've already done such a challenge against the Benchmark DAC1's headphone amp which is a very similar design to The Wire and nobody can hear the difference on any headphones I've tried.

  93. any plans on changing the format of your website from blog to a more standard site? the ammount of info and variety of topics gets diluted with the blog format based on posting date....i really like the comments to the articles, but there has to be a better way of indexin and relating the entire list of articles.

  94. @Anon, No plans right now. I know it's not ideal but the site is taking a lot of time just with the content, reviews and projects. I'm hoping Blogger will enhance their feature set in some ways that might help, but we'll see.

    I could do a "table of contents" offline in HTML and post it as an "article". That would help. But it's just a matter of priorities right now.

  95. When I googled (Jds Labs C421 vs O2),I found that O2 beats c421 in sound quality hands down,but then found the bass boost option of c421 is a very attractive option for various user & they are liking it a lot,but no disregard to Jds labs,so can we see a bass boost option in future O2s.


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