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I was reading the thread about distortion but I'm not sure if my problem is the same so I thought I'd start a new thread. I have the buffalo fed with a toslink wired to D1. The outputs go to XLR jacks, RCA jacks, and a single ended headphone jack. I have a single digital and single analog power supply. The problem is at high volume, I get some distortion on both left and right sides. This happens with both balanced and single ended headphones at about the last 15 degrees or so of volumite travel. I pulled the controller off the board and am using the Buffalo firmware chip for the volumite. Otherwise, the SPDIF switch is set to off and the other switches are in their default positions. I have not cut the traces for the output resistors. Is this the next logical step? Or is there something else I should do first? (EDIT: single ended headphones are Grado SR-80, balanced headphones are Sennheiser HD650.) Edited by user Friday, July 24, 2009 1:38:32 PM(UTC)
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Is it a Buffalo? Or a Buffalo32S?
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Buffalo 32S. The version with the thumpbusters already installed.
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What voltages are you running?
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5V for digital and 15V for analog
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Ok if by 15V you mean +/- 15V then you are ok there.
I would indeed try enabling the output R at least to test. It very easy to undo just by shorting the output R51-R54.
You may also want to send good quality pictures of the top and bottom of the DAC to "quesions" by email.
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Yes +/- 15V. I should have been more precise. Just to be 100% sure, to cut the traces, I cut in parallel with the marks on the board, correct? Also, I was reading in the manual about making sure GND and the AGND pads are connected. I didn't do anything special there (did not short L1 and L2) although the 2 AGNDs are connected since they're using the same power supply. Would that make a difference?
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On the version with integrated thumpbusters, the grounds are already connected on the bottom of the board, so not changes are needed there.
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How about wiring? Is there a minimum gauge recommended for connecting the power supplies to the Buffalo? I'm currently using pretty thin stuff (I think it's 24GA) but I didn't think there was that much juice coming through for that to make a difference.
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24gause should be fine. My best guess is that there is a cold or loose solder joint somewhere. Can you post some pictures (top and bottom)?
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This sounds very much like the distortion that I'm getting. I just received my B32S board back from getting a new Sabre chip installed, and the distortion is unchanged. It distorts as the volume increases. I will post more detailed info in the next day or two. You might look for a DC offset on the output of the op amps. So as to not confuse the two boards and problems, I'll post my findings on the old 'distortion' thread. We may be able to mutually solve our audio problems. BTW oneplustwo, I live in the SF Bay Area.
RossG
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Ross can you send clear pics of the top and bottom (if you already did I will search for them). I would like to make sure all the comps are in the right place and right value. It is possible there was an error in assembly.
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One thing you both may want to do is decrease the output swing by installing R47-R50. 2K would be a good start.
Also if you are going to be heavily loading the DAC I would use 12V analog rails instead of 15V, it will be generally happier and cooler.
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Russ White wrote:Ross can you send clear pics of the top and bottom (if you already did I will search for them). I would like to make sure all the comps are in the right place and right value. It is possible there was an error in assembly. You may recall that Tom, a fellow DIY'er, wrote that he would solder my Sabre chip for me. Afterwards he compared my board to his B32S and all the components were of identical (printed) value and in the same place. What Tom found was a 1.6 offset on the output of the op amps (IC 9, 12) that my AC coupled scope traces failed to show. All the power supply voltages on the Sabre chip measured the same as his working B32S board. Since the problem is happening identically on both channels of my board, Tom was beginning to think that possibly something is wrong with the board, like a through-hole not making contact with both sides. There may also be a failed component. Although he said that with the inputs the op amps were receiving, they seemed to be functioning properly. RossG
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Ross IC9 and IC12 work at a common mode bias voltage of 1.65V. This is perfectly normal.
This is to make the I/V stage work at the same bias voltage as the output of the DAC.
At the second stage of the output (the output terminals on the board) the common mode offset should be close to 0.
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