Noise on R-channel NAD C370 - diyAudio
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Old 18th September 2007, 02:48 PM   #1
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Default Noise on R-channel NAD C370

My NAD C370 is producing static-like noise on just the right channel. Id describe it as a random popping sound. The attached scope plot shows the main output of the right channel (1-red) and left channel (2-blue) on a 200 mV/div vertical scale. The amp has the following symptoms:
1. The noise appears in the right channel only and is present at the PRE OUT 1 (R channel).
2. The noise is independent of volume, balance, treble, or bass. Adjusting any of these controls has no effect on the noise.
3. Physically shaking the amplifier does not have an effect on the noise.
4. The noise is present regardless of the input source.

The receiver was purchased in April 2004. I took it to Precision Audio & Video Services in Seattle for repair in Dec 2005. They were unable to determine the problem and suggested sending it to NAD. My wife went into the hospital that spring and the warranty expired before I could send it in.

Im in need of a service and repair manual for a NAD C370 so I can attempt to trace the signal flow. Id appreciate any other suggestions.
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File Type: jpg c370 rl main out (no input).jpg (51.7 KB, 154 views)
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Old 18th September 2007, 08:25 PM   #2
Bigred is offline Bigred  Canada
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I have a full SM of the C-372 (the 370's successor) that might help also.
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Old 19th September 2007, 02:46 AM   #3
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Thanks for jpg. I would be interested in the C372 service manual. I suspect there a number of differences but the signal flow might be similar.
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Old 19th September 2007, 03:02 AM   #4
anatech is offline anatech  Canada
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Location: Georgetown, On
Hi sandeman,
Normally noise like that will be found near the input or Vas stages. NAD uses transistors for muting the signal like many others do. Remove the muting transistors to see if the noise goes away. If these are the problem, you must install new ones using the exact transistor number. They are made with higher Vbe breakdown ratings and so are different. A relay could be used but modifications would be required.

"Just because you can, doesn't mean you should" my Wife
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Old 25th July 2008, 03:32 PM   #5
Alek74 is offline Alek74  Poland
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I'm new on this forum. I wonder on modification of my NAD C372. Could anyone send me service malual of NAD C372, please ?

Thanks, Alex
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