Hi there,
I got faulty Lite DAC-AH on my hands and now i am trying to repair it.
The problem is that it gives a lot of distortion (like bad signal on radios). Issue is with coaxial and also with optical input so the problem is not there. Also the distortion is same on both channels so i quess its not issue with op-amp circuit.
Measured all regulator output and they seem to be ok. Fixed the common issue with wrong resistors and adjusted TDA1543 dac chip outputs to correct 3.3V. Did not solve the problem.
Heres the circuit:
http://www.audiodesignguide.com/DAC/dac_ah_circuit_new.JPG
What to do next? If one of the eight TDA1543 chips are bad, could that add distortion to the signal?
Thanks in advance.
-Samu
I got faulty Lite DAC-AH on my hands and now i am trying to repair it.
The problem is that it gives a lot of distortion (like bad signal on radios). Issue is with coaxial and also with optical input so the problem is not there. Also the distortion is same on both channels so i quess its not issue with op-amp circuit.
Measured all regulator output and they seem to be ok. Fixed the common issue with wrong resistors and adjusted TDA1543 dac chip outputs to correct 3.3V. Did not solve the problem.
Heres the circuit:
http://www.audiodesignguide.com/DAC/dac_ah_circuit_new.JPG
What to do next? If one of the eight TDA1543 chips are bad, could that add distortion to the signal?
Thanks in advance.
-Samu
Without cable i can hear very high tone, definately not should be there but distortion ends.
DAC chips are in parellar so i quess it is impossible to diagnose those without removing them one by one?
EDIT: Also when i start to play music the distortion sound increases a lot.
EDIT2: Interesting.. DAC chip that is second from top (near to trimpot, see image below) is quite hotter than others.. is this normal?
http://www.diygene.com/store/image/cache/data/dac/dacah_1-1600x1200.jpg
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Mine has a faint high pitched tone as well, I think around 16 kHz, not sure, so that may be normal.
Which DAC chip is hotter? Then I can check mine, can not view your picture right now.
Ill try that chip removing next. Both regulators give steady 6V output and tda outputs are adjusted to 3.3V.
If i have understood right, the dac should work still if it had only one dac chip installed?
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Ok good to hear that pitched tone is normal. U8 seems to be the hottest, the one near the trimpot.
I'd recommend considering replacing the AD847 with sockets as well, then you can try different IC's at the line-out, I did this a few days back and the difference in sound is pretty much like a completely new DAC.
Removing all the solder is a hassle, you need to insert the desoldering pump at all kinds of angles, well I didn't remove the board itself just the two metal covers beneath and above.
Removing all the solder is a hassle, you need to insert the desoldering pump at all kinds of angles, well I didn't remove the board itself just the two metal covers beneath and above.
I am planning to do the passive mod when i have figured out this isue. Already ordered k75-10 2.2uf pio caps.
I must to addmit that i have no clue about current out dacs.
Do you recommed op changes over passive mod? I have just readed about passive mods and people have said that it sounds good.. Is there some electrical problems with the passive mods?
None that I'm aware of - with 8 paralleled chips you might even have enough headroom to implement a passive low-pass filter too to take it to the next level.
Another mod worth doing is disabling the internal current sources (just disconnect all the pin7s) and provide external 'pull-up' CCSs.
Another mod worth doing is disabling the internal current sources (just disconnect all the pin7s) and provide external 'pull-up' CCSs.
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