Nad c325 - noise on one channel
I ask for your help to try to find out the cause of this problem.
Intermittent popcorn-like noise on the left channel.
It is more evident if I leave the amplifier unplugged for several days.
The noise tends to decrease if you leave it running for a long time, after 2 or 3 hours, it decreases considerably but does not disappear.
The noise is also audible through the headphones.
It is independent of the source and volume of the sound.
Curiously in standby the noise persists in the headphones but not in the speakers. ????
I ask for your help to try to find out the cause of this problem.
Intermittent popcorn-like noise on the left channel.
It is more evident if I leave the amplifier unplugged for several days.
The noise tends to decrease if you leave it running for a long time, after 2 or 3 hours, it decreases considerably but does not disappear.
The noise is also audible through the headphones.
It is independent of the source and volume of the sound.
Curiously in standby the noise persists in the headphones but not in the speakers. ????
there is also a hum on both channels under the same conditions as the noise
the pre amplifier part does not suffer from this problem, I connected it to another amplifier and there is no noise.
the pre amplifier part does not suffer from this problem, I connected it to another amplifier and there is no noise.
Pictures.
Electrolytic caps and transistors should be checked because of overheating due to the odd heatsinks. I recall these to run hot but it was long ago and it was NAD so short longevity anyway.
Electrolytic caps and transistors should be checked because of overheating due to the odd heatsinks. I recall these to run hot but it was long ago and it was NAD so short longevity anyway.
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The headphone output comes from the power amplifer output through a two resistor attenuator,
so the noise must be in both the speaker and headphones.
The power amplifier circuit has metal film resistors, and a fair number of semiconductors.
Localizing the noise to one part or connection would be rather difficult, but it does seem like
it could be a semiconductor, although metal film resistors can also develop such noise.
Hum is likely to be an electrolytic capacitor developing high ESR. especially the 15,000uF pair.
so the noise must be in both the speaker and headphones.
The power amplifier circuit has metal film resistors, and a fair number of semiconductors.
Localizing the noise to one part or connection would be rather difficult, but it does seem like
it could be a semiconductor, although metal film resistors can also develop such noise.
Hum is likely to be an electrolytic capacitor developing high ESR. especially the 15,000uF pair.
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It's been on for 24 consecutive hours and the noise has practically disappeared.
From experience, if i unplug it for another 24 hours, the noise returns to the point of going into protection mode.
Is this the expected behavior of failed transistors?
From experience, if i unplug it for another 24 hours, the noise returns to the point of going into protection mode.
Is this the expected behavior of failed transistors?
Sounds to me to be a perfect candidate for very sparing application of freezer spray on suspect parts. Apply a drip at a time on parts, don't blast a whole area.
It could be anything. Do not overlook any small compressed disc type capacitors as they can be troublesome. It could be a transistor, any hot running devices would be suspect which would probably be the VAS stage in the amp.
It could be anything. Do not overlook any small compressed disc type capacitors as they can be troublesome. It could be a transistor, any hot running devices would be suspect which would probably be the VAS stage in the amp.
It could be a transistor, but it could be almost anything.
I was about suggest cold shot, but Mooly beat me. I'd also tap around with a wooden stick. Pure guess, I'm also suspicious of the CON8/CON9 connector pair, as global feedback passes though. Maybe contact cleaner for good measure.
Good luck!
I was about suggest cold shot, but Mooly beat me. I'd also tap around with a wooden stick. Pure guess, I'm also suspicious of the CON8/CON9 connector pair, as global feedback passes though. Maybe contact cleaner for good measure.
Good luck!
This amp is 15 or so years old so let's not forget about worn/dirty contacts on the speaker protection relay(s).
It's earned the #1 position on my list of age related failures because it has happened so many times.
It's earned the #1 position on my list of age related failures because it has happened so many times.
More often than not wrongly chosen relays certainly in classic Japanese amplifiers. Gold contacts don’t work well to switch current.
Have exactly same issue and noise on my NAD 3400 amplifier. Did u sort out what causing this?
Cheers
Cheers