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NAD C370 distorted sound on both channels
NAD C370 distorted sound on both channels
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Old 16th June 2012, 08:31 PM   #1
nemz is offline nemz
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Join Date: Jun 2012
Default NAD C370 distorted sound on both channels

Hi all,

I was hoping someone had come across this problem before, but after searching the forum it seems they haven't.

The symptoms are the volume is very low and distorted, the main four caps look like they stained and the advice from the NAD Salon was to replace these with new capacitors.

Could this be the source of the problem, I'm pretty handy and would take on the repair myself - really miss the sound quality after moving to a Denon AVR

Lee,
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Old 16th June 2012, 11:21 PM   #2
istari knight is offline istari knight  United Kingdom
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Join Date: Sep 2005
Location: Cornwall, UK
Can you upload some pictures ? I suspect the caps have vented, a common fault in earlier editions of this model until NAD changed them to higher temp variants. The original version were 85c & NAD changed them to 105c .... These amps run HOT!

Has it ever been repaired before ?

I have repaired several of these all with the same fault in the protection circuit - Some wouldnt turn on & those that did sounded like you describe...

First two pictures show the protections circuit, third is the schematic. You need to replace all of the capacitors on this board with 105c variants & move the diode to the other side of the board (shown in picture 2) to prevent it cooking the caps again.

Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.

Whether this is the cause of your fault I cannot say but if its not been done it certainly will need doing for the sake of 2 in parts.

Best regards.
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Old 17th June 2012, 10:23 AM   #3
nemz is offline nemz
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Join Date: Jun 2012
Hi Istari,

I replaced those capacitors today and moved the diode - it's resolved the power delay issue, used to take about 5 minutes to come on (one fault sorted) the distortion remains however. I may try replacing the four large capacitors which are 10000uf 80v and check the IC's although I'd imagine it'd be more likely for one channel to go than both at the same time if it was an IC issue - little more googling I think.

Sounded so hopeful, clicked on immediately

Thank you for the fix.

Lee,
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Old 17th June 2012, 11:44 AM   #4
istari knight is offline istari knight  United Kingdom
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Join Date: Sep 2005
Location: Cornwall, UK
Good, Im glad it helped a little!

I would also change the 4 large caps... If still the same afterwards you could try some freeze spray to isolate the fault but as its both channels I'd dedicate your efforts to the power supply(s).
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Old 26th May 2017, 01:08 PM   #5
Colin42 is offline Colin42
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Join Date: May 2017
Hi Istari, Did you resolve the distortion problem. I have the same problem and have discovered that the split rail DC voltage rail is out of balance i.e., +64v and - 50v suggesting a power supply problem possibly in the voltage regulation circuitry. Colin42
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