BEHRINGER UCA202 RCA output coupling cap mod ?? - diyAudio
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Old 10th June 2012, 03:28 AM   #1
AC439 is offline AC439  United States
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Smile BEHRINGER UCA202 RCA output coupling cap mod ??

Hi, I just bought this usb DAC and connecting to my stereo via RCA output. I use this in place of my ipod for using Winamp/Shoutcast for music. I read mods on the headphone section, but I'm using RCA output. There is no mod posted for RCA output. By looking at the pics, there seems to be a coupling output capacitor of 22uF (electrolyte type) to the RCA jacks. I like the MKS/MKP type caps better but they are too big to fit in. Anyone has tried replacing this pair of caps ? What would you use ? I'm thinking about ELNAs as film caps are too big to fit in.

Side note: I used the headphone output from my ipod touch 4G to compare to the UCA202 RCA output to same amp/speaker. They are very close but the ipod seems to be slightly more transparent, detail, warmth and more musical. I believe this is because of the output coupling caps of the UCA202 being electrolytic.

-AC
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Old 13th June 2012, 07:48 PM   #2
AC439 is offline AC439  United States
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Ok, nobody reply yet....

I opened up the case and got into the PCB. I realized that the L/R audio outputs go through an SMT op-amps (8-pins, dual opamps), then a pair of SMT transistors and a few SMT caps/resistors/inductors before the RCA jacks. Definitely more than just output caps. There are few 22uF electrolytics in the signal path.

I think I found one old post here somewhere that someone just got the signal output from the chip (pcm2902e) and feed it to the power amp and stated it was fantastic. I have just downloaded the datasheet and will give it a try. Problem is I want to use MKP caps such as WIMA but large ones can't fit in and the value of the caps are usually large (10uf, 22uf and someone uses 68uf).
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Old 13th June 2012, 08:02 PM   #3
Ar4 is offline Ar4  Latvia
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I do not recommend to do that, because PCM2902 requires LPF at output. I used UCA202, changed opamps, swapped lytics for foil, everything was fine. When I just soldered wires directly to PCM2902 pins, (used 10u cap, depends of load you plan to use, mine was high impedance). sound was worse, there was high frequency noise audible. You can try to use passive LPF. I used active, with dual PSU, to get rid of few capacitors. UCA202 is a nice USB card to play around, and sound pretty good for that price.

Last edited by Ar4; 13th June 2012 at 08:05 PM.
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Old 13th June 2012, 08:36 PM   #4
AC439 is offline AC439  United States
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Thanks for sharing your information. Which foil caps did you use to replace the lytics? The lytics are 22uF. Foil caps will be very big with 22uF. I am also thinking about Elna silmic caps for that. But again it is still lytic caps and wondering if I should do that to keep everything inside the original chassis. Also, which op-amp did you use in place of the original ? (I don't use the headphone output. I'm only concerning the RCA output.)

-AC
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Old 15th June 2012, 07:53 PM   #5
Ar4 is offline Ar4  Latvia
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I used some Vishay 10uf, and they did not fit in the case. Actually I did not even try to put the PCB back, because I added power line bypass capacitors too, used external trafo for opamps, added SE headphone buffer. (yeah, might be too much for 16bit soundcard ) I used different opamps, preffered OPA1642 and LME49720 metal cans. LME was oscilating, had to add local bypass caps, but OPA worked fine. I can't help you with choosing capacitors, because there are not really much free space. Maybe you could use good quality lytic, and bypass it with SMD MKP capacitors, at the bottom of PCB.
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