Hi, I checked the voltage drop on the emitter resitor at each mosfet
and all seems to ok, 12-16mV on 0.47ohm resistors.
There are still a few old small green caps around.
I'm trying to set the offset without any source or speakers on it.
There is a separate pot for the quiescent current.

Thanks!

On Nov 19, 11:33*pm, nospam wrote:
Tonic wrote:
Hi, I have a B&K EX4420 power amplifier with balanced and non-balanced
inputs. I tryed to get rid of the DC offset, each channel has a pot
for correction but it keeps fluctuating. When the amplifier starts I
have around 200mV then after warming up it's fluctuating between -10mV
and 70mV. I changed all the electrolitics inside the amp with no luck.
The amp has 5 pairs of mosfets on each channel, dual mono.

With no source and no loudspeakers connected to the amp I get
fluctuating DC offset when it's switched to the non-balanced inputs.
If I switch to balanced inputs I get 0mV but when I connect a source
it's fluctuating too.
Anyone has a clue about this? or schematics?

Thanks

Guess is that one of the parallel MOSFETS is open circuit or you have a
few dud caps.

You are setting the offset with a load on ?

for example, HH amps hunt up/down if the quiescent current is set
without a load on.