Objective Reviews & Commentary - An Engineer's Perspective

March 15, 2011

Behringer DAC Modifications

behringer uca202 mods top side pcb caseINTRO: The little Behringer UCA202 DAC, for under $29, did surprisingly well in my review.  In all areas but one, the UCA202 is a respectable performer. The photo shows the much larger output capacitors (big black objects above the volume control) laying on their sides that are part of the modification.

PRO-SOUND DESIGN: Behringer likely designed the UCA202’s headphone jack for use with higher impedance studio headphones. While it can drive such phones fairly well, it’s not very compatible with typical consumer 16 – 32 ohm headphones.

WEAK HEADPHONE OUTPUT: The 50 ohm output impedance of the UCA202 limits the volume you can get with low impedance headphones and also causes substantial frequency response variations with certain phones due to how the impedance interaction (see the article on headphone/amp impedance).

Behringer UCA202 Frequency Response No Load (yellow) Ultimate Ears SuperFi's (blue)The graph (click for larger) shows the frequency response of the original UCA202 with no load in yellow and, without changing the levels or volume, what happens when you plug in a pair of Ultimate Ears SuperFi 5 Pro headphones. The balanced armature design of the SuperFi’s create wide impedance swings that cause a total of 14 dB of frequency response deviation (+/- 7dB). The broad midrange boost and high frequency cut is very audible and undesirable.

THE CURE: I wondered if it’s possible to lower the output impedance and raise the output level? If so, the Behringer would be a bargain USB Headphone DAC.

SOME RESEARCH: Unlike similar “disposable” consumer electronics that are often glued or snapped together in a way you have to destroy them to open them up, the UCA202 comes right apart after removing two easily accessible screws. My first observation was the general purpose op amp used to drive the headphones can’t drive lower impedances very well. And there are 47 ohm resistors in series with its outputs (required by the op amp). These further raise the output impedance and limit the output power. I came up with a modification that requires replacing the op amp and four to six other parts.

berhinger uca202 mods IC removedTHE EXPERIMENT: I warmed up the soldering iron and went after the UCA202’s PC board. I replaced the headphone op amp with a much higher quality pin compatible IC. The new amp can much better drive lower impedances at low distortion and generate much more output power from the same power supply voltage. A few other component changes were also required to optimize the new design. The photo shows the old IC removed and the other component locations circled.

THE RESULTS: The table below summarizes the measurements between the original UCA202 and the modified version. The main goals were met with more than 12 times more output power into 16 ohms and the output impedance dropped from 47 ohms to a much more reasonable 2.5 ohms. Using Ultimate Ear’s headphones, the frequency response improved from +/- 7 dB to a much more neutral +/- 1 dB. The other measurements were similar enough to be the same (better results are in bold):

behringer uca202 vs nwavguy version








LISTENING TEST: In the Listening Test the modified version scored a slightly better than the unmodified version’s headphone outputs. But I used headphones in the test with a relatively constant impedance so the frequency response changes were minimal. The listening level was also (barely) within the unmodified versions power capability. Changing the headphones, or raising the volume, would have yielded a much more obvious advantage for the modified version.

NOTE TO BEHRINGER: Behringer could, if they wanted, mass produce a similarly improved version of the UCA202 and the retail price would only need to be increased by less than $10. The changes I made would raise their wholesale component costs by less than $2. Unlike the current model, the new $35 – $39 USB DAC would meet the headphone needs of both professionals and consumers. It would suit a much wider range of headphone types and play significantly louder with any headphones with more accurate frequency response.

NOTE TO OTHER USB DAC MANUFACTURES: This experiment, along with the original UCA202 Review, show what can be done with an inexpensive USB headphone DAC. It’s my opinion if any company is going to charge several times more, and can’t at least equal this level of performance, they’re probably not offering a good value for their customers.

BOTTOM LINE: I was pleased with the above results. The main purpose of this rather academic experiment was to prove: It’s entirely possibly to design, manufacture, and sell through retailers, a high quality headphone DAC for $39 or less. The bad news is, as explained in the Tech Section below, it’s not practical for most to perform the modifications. And I’m not holding my breath Behringer will offer an improved version given their target market. And if you paid someone else to do it, the total cost (including the UCA202, labor, and parts) would probably spend around $100. And, at that price, there are likely some better options that don’t require modifications (i.e. the $99 FiiO E7, $99 Firestone Fireye2, etc.). As always, I welcome comments and feedback!

TECHNICAL SECTION (all the details):

WHAT DIDN’T CHANGE: Because only the headphone amp was changed, the performance of the DAC chip itself, and the line outputs should remain the same. I did some quick checks to verify the line output performance, DAC linearity, jitter, etc. were similar to my earlier review. They were.

DIFFERENT TEST LOAD USED: The original UCA202 did so poorly with my usual 15 ohm load, I used a 150 ohm load for most of the headphone output tests. But this makes comparing the UCA202’s headphone performance to other devices I’ve tested more difficult. So, for these tests (unless otherwise noted) I used my standard 15 ohm test. Note this is a much more challenging load, so in some ways, one can expect degraded performance from the previous 150 ohm measurements.

MAXIMUM OUTPUT: The original UCA202 had a hard time with my 15 ohm test load. It only managed 179 mV RMS at 1.3% THD+N which is 2 mW into 16 ohms. Here’s the plot:

Behringer UCA202 1 Khz 0 dBFS 44.1 Khz USB Headphone 15 Ohm Clipping Point (ref ~ 180 mV)

And here’s the modified version doing more than twelve times better better at 635 mV which is over 25 mW into 16 ohms:

Modified UCA202 1 Khz 0 dBFS 15 Ohms Max Output (Ref ~400mv)

And because the new amp IC can swing closer to the supply rails, even with 150 ohms, it has an advantage. Here’s the original max output at 150 ohms of 668 mV or about 3 mW with the volume set as high as possible for < 1% THD+N:

Behringer UCA202 11025 hz 0 dBFS 44.1 Khz USB 150 Ohms Bal Max Output Clip (ref ~400 mV)

Here’s the modified version into the same 150 ohm load with nearly 4 times as much power (11.3 mW) this is with volume control all the way up at 0 dBFS:

Modified UCA202 1 Khz 0 dBFS 150 Ohms Max Output (Ref 400 mV)

THD+N AT REFERENCE LEVEL: At the reference level of 400 mV RMS here’s the original driving the relatively easy 150 ohm load:

Behringer UCA202 1 Khz 0 dBFS 44.1 Khz USB 150 Ohms Reference Level (~400 mV) THD and THD N

And here’s the modified version, same level, but into a much more challenging 15 ohm load. The distortion is virtually identical to the above measurement and likely determined more by the DAC chip and implementation than the new headphone amp (anything below 0.01% is widely considered inaudible anyway):

Modified UCA202 1 Khz 0 dBFS 15 Ohms THD at Reference Level of ~400mv RMS

OUTPUT IMPEDANCE: Besides output level, the other big problem with the original UCA202 is the approximately 50 ohm output impedance. Here’s the modified version with no load referenced to the same 400 mV level used above. Knowing the no load (source) voltage is 467mV and the voltage with the 15 ohm load is 400 mV, the output impedance calculates out to 2.5 ohms which is a huge improvement and very close to my ideal of 2 ohms or less. I’m not sure yet why it’s not closer to 1 ohm but I suspect it’s at least partly the output capacitors I used (more on those later):

Modified UCA202 1 Khz 0 dBFS No Load For Output Impedance (Ref 400 mV)

NOISE:  The A Weighted output noise previously measured –92.0 dBA while the modified version measures a nearly identical –91.4 dBA. A difference of 0.6 dB is not generally considered audible. The 47 ohm series resistor in the old design was attenuating the output noise with a 150 ohm load by about 2 dB. Considering the new amp doesn’t have such an attenuator, it’s noise performance is actually better. The new amp IC has better noise specs than the original so this is what you would expect. And the remaining noise appears to be from the DAC itself. So, for all practical purposes, the noise performance is the same:

Modified UCA202 1 Khz -115 dBFS 15 Ohms Noise (Ref ~400mv RMS)

SWEPT THD+N: The original UCA202 did well on this test and the modified version does even better despite driving a much more challenging load (15 ohms vs 150 ohms). The original is shown in red, the modified version in blue, and the NuForce uDAC-2 in green (note the vertical scale is expanded to a max of 0.1% compared to the NuForce uDAC-2 Review):

Modified UCA202 -3 dBFS THD N Sweep 15 Ohms (Ref ~400mv RMS)

CHANNEL BALANCE: Channel balance is very load dependent. There are multiple reasons for this. More challenging loads cause the power supply (which is shared between both channels) to have more “load ripple” which is essentially the audio signal being superimposed on the power supply. Another reason is higher loads create higher currents and higher currents create more electromagnetic radiation which “cross couples” between the channels. This happens both inside IC’s shared between both channels (like the headphone amp IC is in the UCA202) and even between tracks and passive components on the circuit board. So I wasn’t surprised the UCA202 did much worse at 15 ohms compared to 150 ohms. If you compare the 150 ohm performance with the modified amp, however, you’ll see the result is unchanged. So the red line below isn’t a result of the modification, but mainly the much more challenging load. It’s not a great measurement at about –38 dB. But, especially for headphone use where a lot of people add far more “crossfeed” on purpose, it’s likely not a significant problem:

Modified UCA202 Swept Ch Sep 0 dBFS (Ref 400 mV)

FREQUENCY RESPONSE: Because the UCA202 lacks a split power supply, or bridged amplifier design, it uses AC coupled amplifiers and outputs. So in both versions, the headphone amp requires an output capacitor in each channel to block DC from reaching the headphones. Into 50+ ohm loads a relatively small capacitor works fine. The original UCA202 uses 100 uF output caps. With a 15 ohm load, however, the –3 dB low frequency roll off changes dramatically. So I increased the size of the output capacitors to help compensate for this. The values I used create a low frequency roll of only about –0.2 dB at 20 hz even with this worst case load. There’s also a high frequency rise that can likely be easily fixed. The new amp IC is “faster” than the old one, and hence requires different feedback compensation. I don’t have the right small value surface mount capacitors on hand to tweak the feedback loop. So I left the original Behringer compensation and it’s causing about a 0.4 dB rise at 10 Khz as shown (the original UCA202 is shown in yellow):

Modified UCA202 -3 dBFS 15 Ohms Freq Sweep (blue) Original (yellow 150 ohms)

And here’s a composite plot showing the frequency response of both versions with a variety of loads taken at the same relative level. The most interesting thing to compare is the blue plot of the original UCA202 driving Ultimate Ears SuperFi 5 Pro headphones versus the red plot showing the new version driving the same headphones. You can also see the massive drop in output and low frequency roll off with a 15 ohm resistive load in orange versus the modified version in green:

Modified UCA202 vs Original Frequency Response Various Loads -3 dBFS (see legend) with comments

OTHER TWEAKS: As mentioned above, the feedback loop could use some attention. Optimizing the feedback should remove the slight 0.4 dB rise at the highest frequencies and might improve the sound. And I suspect using higher quality output capacitors might lower the output impedance still further. The problem here is finding better parts that will fit inside the original case. All my modifications fit completely inside (although I did have to cut a plastic post off the inside of the case). Better audio-grade output capacitors (and possibly adding quality bypass caps) may also improve the sound quality and further lower the output impedance. It might also be possible to improve the channel separation with some tweaks to the power supply lines feeding the new amp IC.

smt resistor pencilTHE BAD NEWS: This is mostly an “academic experiment” as few have the tools or skills for the surface mount re-work these modifications require. As can be seen in the photo, surface mount components are incredibly small and not made for human soldering (machines do it all when the boards are made). The photo shows three surface mount resistors in their original paper “tape” next to a regular pencil. The entire parts are smaller than the tips on most soldering irons.

THE DETAILS (added 3/25): I’ve received several messages and emails wanting to know the details of the modification. My plan was to research the issues mentioned above and then publish the final component values. However, for those of you who are just curious, here are the details. I want to stress that anyone who doesn’t have enough surface mount soldering/re-work experience could easily damage their UCA202 beyond repair attempting these modifications. And I also have not explored the high frequency “peak”, tried to improve the channel separation, or explored the somewhat higher than expected output impedance. So for anyone attempting this modification, please be aware it is presented “as is”, has not been fully developed, and you may damage your UCA202!

I chose an Analog Devices AD8656 op amp. It’s designed for high quality audio use from a 5 volt power supply with very low distortion and noise. And, equally important, it has +/- 75 mA of peak current capability to better drive low impedance loads directly along with a “rail-to-rail” output increasing the power available for higher impedance headphones. For a high-end op amp it’s also relatively inexpensive in single piece quantities at $2.75 (I wanted to keep the total parts cost < $5). If cost is not an issue, I would consider the $5.22 AD8397 as it has +/- 310 mA of peak current capability and is used in many respected commercial products as the headphone amp although it’s not optimized for a single 5 volt power supply.

I replaced the series 47 ohm Behringer output resistors (circled in the photo earlier) with 1 ohm 0603 SMT resistors shown next to the pencil in the photo. And I replaced the 100 uF Behringer output capacitors (pads circled) with 2200 uF 6.3v capacitors you can see at the start of the article (laying on their sides). I had to cut one of the internal plastic posts from the case (also visible in the phone) to make room for the larger caps.

FINAL WORDS: All things considered, for a fairly simple “hack”, I was rather pleased with how this turned out. The modified Behringer UCA202 has enough power to satisfy most anyone (significantly more power than a Sansa Clip+ for example). And the output impedance drops from a very poor 50 ohms to only 2.5 ohms. It retains its previously low distortion, similar noise levels, and most other characteristics. The very slight ( +/- 0.3 dB total) frequency response variations are inaudible but I’d feel better about this modification with the feedback compensation adjusted for the new amp IC. But I have to order some parts to do that. If enough people are interested, I can take this project further?


  1. Color me interested in further modification! It's always cool to see cheap upgrades make a big difference.

    Too bad the process requires super-human skills, though. Do you think some of the easier parts, like output caps, can make a difference on their own, or is the modification pointless without the tiny resistors?

  2. You could jumper across the two 47 ohm resistors rather than replace them as I did. But even that requires a really fine tip soldering iron and a steady hand. Replacing the op amp IC also isn't easy--especially getting the old one off without damaging the PC board. And the IC is the "heart" of the modification.

  3. I see. Nevertheless - if you do decide to take this project further and write about it - it would be nice to have more insight into the actual modification process. What parts did you choose, why did you choose them etc. While knowing that the Behringer can be improved like this is nice, it would be of more value to benefit from your research by reproducing the hacks ourselves, even if it's likely to damage the PCB in the process.

  4. I recently bought a Behringer UCA202 based on your recommendation and have been very pleased with the noticeably improved music that it's able to deliver. I've been pairing it with my trusty Grado SR80i headphones, which have a listed "normal impedance" of 32ohms. You said that the Behringer is "not very compatible with typical consumer 16 – 32 ohm headphones". Do you think my Grado headphones are definitely still not getting ideal sound from the Behringer? Is it possible they're NOT being affected adversely? Like I said it sounds nicer than I've ever heard headphones sound, but on quiet sources (like a movie with a low mix), I have to turn the volume up to almost max or all the way max.

    Link to the Grado spec page:

  5. Oops I just checked your Behringer UCA202 review from late last month and it seems that "will it work well with my headphones" is becoming a common refrain. I don't mean to pile on. I do want to thank you, however, for putting together this blog, it has been a real eye-opener for me and a really fun read. It's great!

  6. In case you were not aware, a polish fellow also did a mod to a Behringer converting it to balanced.


    I'd be curious, would you mind testing the Behringer with a 5V battery pack or regulated 5V input instead of USB power and see if it has any effect on the noise floor?

  7. To Traf, I'll consider a follow up article, or modifying this article in the future. I need to fix the compensation problem I mentioned, and also explore other output caps. I'm also hesitant to turn this into a true DIY project as I'd hate to see anyone ruin their UCA202 because of me.

    To Scott Anthony, if you're having to turn the UCA202 all the way up at times with your Grado's I'd say you could probably benefit from a DAC with a lower output impedance that's better able to drive a 32 ohm load. The frequency response may also change in audible ways. One cheap solution might be to add the FiiO E5 to the UCA202 (a combination I haven't yet tried). But then you have another device to power, another cable, etc. See my E5 review.

    To K. Brant, thanks for the link. I'll consider testing the UCA202 with a different power source, but that's not a very realistic option for most people. I would rather explore improving the filtering of the USB power within the UCA202. I checked the power supply noise and there's a tiny amount of high frequency "hash" but the bigger problem is likely a fair amount of "load ripple" when driving low impedance loads (I think that's the main cause of the poor channel separation I measured). I don't think Behringer designed the DAC's power filter to provide the peak current the new headphone amp circuit can require.

  8. I agree with you that using alternate power for the Behringer wouldn't be a good option for most people. There are plenty of guys that have modded various portable USB dacs to run on battery packs but IMO this is a PITA and impractical.

    Anyway, where I was going with this was by running Behringer on alternate power and taking some measurements, you can establish a baseline and determine if it is even worth it to work on a power filter or not, or if it would be worth it for a guy to run the thing on a battery or whatever if he so chose. You can also have a better idea of how well a power filter is working or how much it could be improved, on the assumption that the a filter solution would land somewhere between stock dirty USB and clean regulated.

    You have better testing equipment than me and can do this kind of stuff :) Anyway you have things well in hand in either case, thanks for your work and your blog.

  9. Your blog has been a wonderful source of useful information, and your Behringer UCA202 review made me change my mind and buy this cheap DAC to drive my Audio Technica's ATH-M50 headphones on my laptop.

    I'm also interested in this project, as my ATH-M50's have a low impedance (38 ohms) and would probably benefit from your changes. It would be nice, like Traf suggested, to see further improvements to the mod, but with parts that can be put on PCB using a regular soldering iron by a not so skilled guy (not afraid of killing the device :-p).

    Anyway, keep up the good work, it's has been a joy to discover this blog and reading your posts!

  10. Hi!
    What kind of headphone output opamp/buffer have you been using for the mod?

  11. Are there any mods to improve the RCA outs?

  12. Richard, I added the details of the components used to the Tech Section above. Please note, I'm not suggesting others attempt this modification and I also have not explored the cause of the slight peak in high frequency response.

  13. I bought UCA202 for simple acoustic/electronic measurement use. I quickly checked the performance, and found the problem. left and right timing is 1 sample different, both of output and input !
    I checked TI website and found the reason...

    > Inter-Channel Phase Difference
    >The PCM290X has delay of 1 sample at each channels as >follows:
    >• Up-stream data from ADC, S/PDIF in : Rch data delay >(1 sample)
    >• Down-stream data to DAC, S/PDIF out : Lch data delay >(1 sample


    With loop-back measurement in RMAA, it seems to be correct, because down-stream and up-steam difference is opposite...

    Have you found this issue on your UCA202 ?
    It is amazing silly mistake, and a lot of peaple using the audio device using PCM290X without knowing the problem.....


  14. You mentioned the Fireye2 as alternative, which wouldn't need modifications.
    I'm curious if you did measure one of them?

    PS: Your blog is a great reading. Thanks!

  15. I have not tested any of the Fireye products. I do plan to test the Asus Xonar U3 and Creative X-Fi USB headphone DACs.

  16. A big thanks for posting this information on the UCA202.

    I have a AKG 600 ohm headphones, and although the sound will not play very loud, it is beautifully clear--much better than my Turtle Beach Santa Cruz card. For the most of my listening the sound is loud enough.

    On my Senheiser HD 580 (300 ohm) plays adequately loud.

    I find the headphone output intolerable and never use it. I would consider modifying it with a better audio chip, but I would first like to solve a more serious problem.

    There is form of jitter that manifests as a wandering tone. Musicians, holding a steady note go from sharp to flat, and the more I hear it, the more disconcerting the effect. I can find no other discussion on the web of this effect.

    I believe that the root cause is the asynchronous feed of the USB signal to the PCM2902 chip. To keep the buffer from overfilling or going empty, the timing system onspeeds up and slows down. The result is a wandering tone.

    It would be lovely if there is a simple modification that would rectify this problem.

    Am I the only one that hears this?

    Furthermore, have other USB dacs solved this problem, or is it something that is just ignored?

    The engineer working for Texas Instrument that developed this chip discusses the problem in a article at this website:


    Neil S

  17. The PCM2xxx chips are widely used in lots of commercial DACs--often just as the USB tranceiver with another DAC performing the D/A function. I agree they don't have the lowest jitter, but I've not heard what you describe. It also tested well when I ran what's widely considered to be one of the better jitter tests.

    I think if the jitter problem with the PCM2xxx was that severe there would be a lot more complaints. It's literally in dozens, if not hundreds, of different products--some of which are fairly high-end.

    I would suggest that what you're hearing might be from another cause, or there's something wrong with your UCA202, or it could even be imagined (see Subjective vs Objective).

    The whole async debate is not what some claim it is. If you read my "CD's are so 1980's" article I talk about some of that. Basically the data packets going over USB have little to do with a digital audio S/PDIF or I2S data packet. So "jitter" on the USB interface doesn't directly translate into digital audio jitter. There's also more in my article on Jitter.

  18. I tried out my UCA202 on two other computers and tone showed no evidence of wavering. I feel a bit foolish I had not tried this before writing to you.

    There is obviously something wrong with the USB feed from the computer that gives the wavering tone. Thank you for your comments.

    I am interested in doing some mods, even if I need to put the UCA202 in a larger case. What mods can you suggest?

    I plan on getting a second one to modify and keep it on the desk. For the time being keep the first, unmodified one for portable use.

    Used ones can be obtained for a very reasonable cost, so the risk of damaging it is not too great.

    Neil S

  19. Beyond the modifications I described in this article, I'm not sure anything else is worth doing with the UCA202. The biggest issue is using good output capacitors and getting clean power to the AD8656 op amp.

    I'm going to be testing the Asus Xonar U3 which is only $40 and may be a much better solution for not much more money.

  20. I'm not a DIY kind of guy, so I'll wait for the commercial version of O2, or some kit that only needs putting together. But I will get it for sure!
    I want to make a suggestion: could you cross boundaries and go in the DAC world too? D2 could be a nice name for a small DAC, suited for laptop use and not only.
    You're great, man! Thank you!

  21. In the article, the possible usage of a AD8397 is mentioned. Looking at the data sheet it appears that even though it is not optimized for 5V, a part for part replacement is still possible with improved output parameters over the AD8656. Am I correct in that assumption?

    (I am asking because I was able to acquire a AD8397 but not a AD8656. Go figure!)


  22. Both the 8656 and 8397 will probably perform similarly. I'm not crazy about CMOS op amps for high-end audio use. Every one I've ever tested has been much worse than conventional op amps. I talk about that in my Op Amp Myths and Op Amp Measurements articles.

    The 8397 is bipolar, the 8656 is CMOS. I haven't tested the 8656 but I did test the 8397. So at least you can get the results I achieved if you use the 8397.

  23. Thanks NwAvGuy - took a look though your op-amp articles as well as some of the more laborious 'audio engineering society' journal articles (thank-you university sponsored journal subscriptions).

    Just finished the substitution of the AD8397 as opposed to the slightly cheaper AD8656 - similar test results were obtained to those mentioned in the article. A digital oscilloscope (picoscope) was used for measurement.

    Comments on the modification process:
    The modification was not as difficult as anticipated. The solder masking on the board is reasonably well prepared, making it easy to solder the new IC on without too high a level of accuracy. HOWEVER! the UAC202 I received had the IC glued to the board! One particular dab of glue intersected a solder tack (crossed the top line of the IC box in NwAcGuy's photo). Removal of the damaged the track, resulting in an hour and a half of repair work.

    In any case, I found this to a be a most worthwhile hack.

    NwAvGuy, thank you very much for the effort you have already put in! Would you consider any further design work to correct the feedback compensation?


  24. I am currently trying to set the uca202 in a better encasing because the onboard volume trimmer really sucks in day to day usage. I removed the volume trimmer which is a 20k log stereo poti. My plan is to use an ALPS poti instead. Unfortunately the only have 10k and 50k but not 20k. I now ordered the 50k because I assume with 10k I will not be able to completely mute the output lines.

    Just for reference if others are also interested. If you look on the back of the board as in the 2nd picture here in this article you see the 5 soldering points in a row. I named them a, b, c, d, e from left to right.

    the channel assignment is a,c,e and b,d,e with e as the shared pin between the two channels and c, d as variable pins.

  25. I'm inspired to try the same type of mod with AD8656. But is the correct component size here the 8SOIC or 8MSOP ?

  26. I'm reasonably certain it's an SOIC-8. Due be aware stability may be an issue with other op amps. The power supply circuitry doesn't have an ultra low impedance at RF frequencies which is required to keep many fast op amps happy. There's also the issue of isolating the reactive headphone load. See my two Op Amp articles for more.

  27. I put the SOIC-8 AD8656 in there, followed by similar coupling caps bypassed by a couple of small WIMA film caps. I also shorted the mentioned resistors. A very worthwhile and fun upgrade! My UCA202 is now full-range with my lo-imp headphones!

  28. Hi NwAvGuy,
    following your very interesting blog, and your review of Behringer UCA202 interface, I bought an updated UCA 202.
    My intention was to use it as a cheap measurement interface (I have since a long time being developing audio measurement software, and would really like to develop a relatively affordable audio measurement system, hardware and software).
    What I discovered is that the headphone chip is now a JRC4556A (instead of a 4558). I suppose it has far better output current capability. Maybe just shorting the output 47 Ohm resistors (still in place) will be sufficient to have a good cheap headphone amp.
    What do you suggest? Have you reconstructed a schematics that can help in tweaking?
    Thank you, and thank you so much for your very enjoyable blog.

  29. @dZingoni, I'm glad you like the blog. That's interesting with the UCA202. Behringer didn't change the UCA202 in many years as I have one of the early ones and also one I purchased earlier this year that did not have the 4556. I don't have schematics.

    Yes, I would just short out the 47 ohm resistors. The 4556 isn't very happy on only 4.5 volts, so there's still benefit to using an op amp designed for low voltage supplies and rail-to-rail operation but it does have much better low impedance drive capability than the 4558.

    For an affordable measurement system I would strongly suggest a better audio interface as the UCA202's relatively high noise floor is going to limit many measurements (including distortion). And the capacitor coupled outputs don't help either. But it comes down to how much you want to spend.

  30. Anonymous, 1 sample time difference is like a positional difference of a tiny little bit of a degree... not critical obviously, probably exceptionally hard to spot :)

    Anonymous nr. other: obviously USB endpoint must adjust the number of samples it requests, but it's a Good Thing, because it allows the endpoint to run its own high precision clock! Samples being output at that rate, there can be no wow&flutter at all - worst case, you should get a jump or a dropout. Maybe the problem is electric and try not to use a DAC on PC's front USB ports, don't power from hubs. NwAvGuy: is there anything at all which can cause an XTal to drift back and forth?

    If you really think it's a software problem on your PC, would be curious to know whether e.g. that's the only XP run computer you use while others run Vista/7, and whether you can exclude that other sounds were playing through onboard soundcard first or simultaneously? I have some thoughts there, but no specific explanation, just things to perhaps experiment with.

  31. @Siana, I'm not sure what you're asking? All crystal oscillators have some degree of what's typically called "phase error" or similar. It's jitter--time variations from one clock period to the next. Cheap oscillators usually have more jitter. And all oscillators exhibit some frequency drift with age and temperature usually measured in parts per million. It's the same in nearly any battery powered clock. They might gain a few seconds a month when kept in a cold place and lose a few seconds a month in the summer months. But it's hard to imagine it being great enough to be detectable even by someone highly sensitive to musical pitch errors. The bigger problem is the jitter.

  32. Regarding the output caps, what would happen if I replace 100 µF caps with really big ones (4700 µF)? Will there be high-frequency roll-off or large amounts of current release when the device powers down?

    1. You don't need to go over 470uF. And it would be good to bypass those with a 1 uF film capacitor in parallel. If you go too big it might on the op amp on power and power down, and yes, it will make and even bigger transient on power up/down.


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