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Wow Tom, that is very kind of you. Ross, I hope it works out! :) We have the greatest members ever. :) Cheers! Russ Edited by user Thursday, June 11, 2009 3:24:00 PM(UTC)
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So thanks to Tom, I now have a new Sabre32 chip on my B32S board, but the distortion at high (medium to high) volume was unaffected by the chip replacement. I was checking IC 9 and 12. Under quescent conditions the voltages are
pin 1: 1.656
pin 2: 1.653
pin 3: +15.00
pin 4: 1.656
pin 5: 1.654
pin 6: -15.00
pin 7: 14.90
pin 8: 1.654
Pin 2 (Vocm) under signal conditions is doing something strange. I apply a -6dB 1KHz sine wave to the board, via direct SPDIF coax connection to the board. On pin 2 of both IC 9 & 12, there is a 1kHz square wave superimposed on the 1.653 quiescent voltage! This square wave is 50mV above the quiescent voltage for 400 microseconds, and then it's 50 mV below the quescent voltage for 600 microseconds (which adds up to the period of the 1kHz sine wave input.) Also, the freqency of the square wave follows the input frequency that I'm sending to the board. When I play a 400Hz sine wave, the square wave on pin 2 now has a period of 2.5 mS (the period of the 400Hz input). Pin 2 on IC 11 and 10 are -2.5mV and -3.7mV respectively. Is this square wave normal?
I'll have scope photos of the signals tomorrow.
RossG
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Regarding VOCM, It is normal for it to move, but it might be more than usual, which makes me wonder whats going on at the second stage. The voltages look just fine at IC9 and 12. I would concentrate down stream. Edited by user Thursday, July 30, 2009 10:02:45 AM(UTC)
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I guess I'll wait and see how your trouble shooting concludes before trying to do anything with mine! Krgaunt - did you cut the traces to enable the output resistors? How about installing R47-50? Those were my next steps but I wanted to see if you had done it yet. Also, did you try lowering the analog voltage to 12V? Edited by user Saturday, August 1, 2009 4:37:13 PM(UTC)
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oneplustwo wrote:I guess I'll wait and see how your trouble shooting concludes before trying to do anything with mine!
Krgaunt - did you cut the traces to enable the output resistors? How about installing R47-50? Those were my next steps but I wanted to see if you had done it yet. Also, did you try lowering the analog voltage to 12V? I did cut the traces to enable the resistors. The distortion is unaffected by lowering the AV to +-12V. I have not installed R47-50 because I believe the problem with my board lies upstream. RossG
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Here is a scope trace of IC 9 pins 1 and 8. The scope trace is exaclty the same on IC12, so all of the below pictures apply to what's going on on the other half of the board. I think the distortion problem that I'm having is near IC 9 & 12, and not at the output terminals. The below pictures I believe will bear this out. There is something that's common to IC 9 & 12 that is causing this voltage fluctuation which results in the distorted output. Changing the Sabre chip has had no affect on this distortion. Here you see the inputs of IC 9 and 12 when a 1kHz -6dB sine wave is input to the board. My friend Tom, who compared my board to his, said that his B32S shows no voltage fluctuation with the same sine-wave input. (I mailed him a copy of my test CD). RossG krgaunt attached the following image(s):  IC9-pin-8_1.jpg (82kb) downloaded 277 time(s).You cannot view/download attachments. Try to login or register.
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Next scopt shot. Here is a comparison of IC 9 (IC 12) Vin+ and Vout+ (pin 8 and 4 respectively) Note how the output is not a sine wave. When Tom did this test on his working board (same sinewave input applied), the outputs of Pin 4 and 8 are sine waves. krgaunt attached the following image(s): IC9-pin-8_4.jpg (84kb) downloaded 276 time(s).You cannot view/download attachments. Try to login or register.
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Here is the outputs of IC 9 (IC 12). This should look like two inverted sine waves. Notice the fold over with respect to the 1.65 quiescent voltage point. One though I have, this output looks as if the ICs are being starved of current, or something is causing too much bias current. It looks like the sinewave reaches a point where a lack of current (or a current limit) is causing the output voltage to sag. krgaunt attached the following image(s): IC9-output.jpg (82kb) downloaded 273 time(s).You cannot view/download attachments. Try to login or register.
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Here is the output of IC 10. The output of IC 11 looks identical. These two op amps seems to be functioning just fine, given the input from IC 9 and 12. Pins 1 & 8 of IC 10 and 11 are at the normal 0.82V bias level with no voltage fluctuation when a signal is applied. So there seems to me something wrong on my board with the current bias of ICs 9 & 12. krgaunt attached the following image(s): IC10-output.jpg (87kb) downloaded 273 time(s).You cannot view/download attachments. Try to login or register.
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Have you tried replacing those opamps? I think your previous incident with the board may well have killed them.
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Russ White wrote:Have you tried replacing those opamps? I think your previous incident with the board may well have killed them. Do you have the DigiKey or Mouser part number?
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Mouser:
595-OPA1632D
DigiKey:
296-16679-5-ND
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Thanks, I'll give that a shot.
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Finally! It works! I replaced all 4 op amps and I finally get a full undistorted sine wave. And the music....Ahhhhhh.  Huge thanks to Russ and Tom for all your time and support in dealing with this. Now it's time to pop on the headphones and quaff a tall cool one. Ross
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Excellent Ross. :) I was pretty sure that would work. I also commend Tom for helping out like he did. Bravo. Enjoy!!! Cheers! Russ Edited by user Wednesday, August 12, 2009 5:05:05 AM(UTC)
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Congrats on the fix! I guess I should try cutting the traces first and seeing if that helps before going so far as to replace the opamps?
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Personally, I prefer to not cut traces, they can be a bitch to resolder. I believe that could mess up Russ' low-noise pathway. The op amps are only $5 each. In reading the TI literature, the op amps are sensitive to heat and static electricity. So trying to remove them for testing and then resoldering the original chips will increase your chances of doing damage to them. For me, replacing all 4 chips was quick and easy. I thought that was a better way to go than replace one or two and see if that solved the problem. I changed them all out and got the board running straight away.
Of course, the problem may not be with the op amps. If you get to the point of needing to replace the Sabre chip, I may have new-unused one that I can sell you.
Do you have any scope traces on the inputs of the op amps? What are your voltages on pins 1 & 8 of IC 9 & 12?
RossG
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