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Old 4th January 2009, 07:55 AM   #1
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Default Two noise problems on two different NAD 216 THX

Hi,

I hope you can help me with this two odd noise issues I have on my two NAD 216 THX amplifiers for biamping.

1. In the first amplifier, the problem appears occasionally on the left channel, usually after several days of rest. The noise seems to be white, random, and I cannot hear any 100Hz broom so I don't suspect any power supply problem,oherwise it would probably appear on both channels. Noise can be heard on the loudspeakers and seen on the oscilloscope (amplitude around 4Vpk, if I remember correct), and is independent on whether the input is plugged in or not, with or without signal. I think that the output music in the presence of noise is somewhat more quiet, but maybe the feeling is only subjective.

The real problem is that whenever I try to investigate it thoroughly with an oscilloscope, a touch with a probe somewhere at the input will remove all the noise and the amp is "repared" until next time (usually few weeks afterwards). I was suspecting a bad soldering and tried to warm up all the input section, and this again solved the problem until few days ago.

Any clue about what the source of the problem is?

2. On the second amplifier, when playing piano music with a certain volume level, it sounds like the right channel creates noise where only the strongest tones come through, kind of level detector. Reducing the volume level somewhat or increasing it seems to solve the problem. I suspected the cables and the preamplifier, but switching around the input and output cables shows the problem being persistently in the right channel of the amplifier.

I haven't looked at the amp with an oscilloscope, and I don't know whether the problem will show up without loading - which might reveal a bad contact problem? Shaking the connectors doesn't help, although I do remember experiencing the same problem before, which vanished when touching the cables.

Hope you can help with explaining what is going on...

Best regards,
Petar
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Old 4th January 2009, 01:05 PM   #2
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Default Re: Two noise problems on two different NAD 216 THX

Quote:
Originally posted by ratep2001

1. In the first amplifier, the problem appears occasionally on the left channel, usually after several days of rest. Noise can be heard on the loudspeakers and seen on the oscilloscope
The real problem is that whenever I try to investigate it thoroughly with an oscilloscope, a touch with a probe somewhere at the input will remove all the noise and the amp is "repared" until next time (usually few weeks afterwards). I was suspecting a bad soldering and tried to warm up all the input section, and this again solved the problem until few days ago.


Hi
I have repaired an amp with a intermittent noise problem similar to yours. Problem was a faulty small signal transistor. I used a heat gun and cool spray with a pinpoint straw to trouble shoot.

Quote:
Originally posted by ratep2001

Amp2. ... Reducing the volume level somewhat or increasing it seems to solve the problem.

suspected the cables and the preamplifier, but switching around the input and output cables shows the problem being persistently in the right channel of the amplifier.

... although I do remember experiencing the same problem before, which vanished when touching the cables.


More trouble shooting needed here for better clues. Are you sure about problem being in the power amp no. 2 right channel? But from your other discriptions, sounds like a dirty connection or pot.
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