Nad c325 - noise on one channel

[martinho1974]

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. ?
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.

[shakalnokturn]

I repaired a NAD C315BEE recently if the C325 is anything similar this may be of some use.

NAD have as far as I know always suffered from weak solders, these Lead-free designs are no exception the C315 needed a lot of reflowing. This could be the cause of your "popcorn".

In the C315 the main power supply filter capacitors where rated for 50V while fed with 45V, very low margin! One of them had bulged and lost enough capacity to cause hum.

[martinho1974]

Correct me if I'm wrong.
If the problem is  only in1 channel, and if it decreases as the temperature increases, this limits the area to look for, on the left amplifier part, and on bad joints or faulty transistors


 https://youtube.com/shorts/jYwfrlkJ6T8?feature=share3

[David_AVD]

Get yourself a can of freeze spray and see if you can narrow down the issue to a specific component. A transistor will be the likely cause for this noise.

[martinho1974]

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 cpoint of going into protection mode.
Is this the expected behavior of failed transistors?

[David_AVD]

Transistors can fail in all sorts of weird ways. It's hard to know if they are definitely the issue in your case.

If you don't have freeze spray (yet), may try heating the bad channel with a heat gun on low (or a hair dryer) to see if that makes the noise go away faster.