Electrocompaniet DC offset

[legarem]

Hi

I had bias problems and now everything is working but I have a major DC offset of near 250 mv I can't eliminate with the trim pot. The voltage V+ feeding the first stage is 40V and the V- is 36V. Could it be the problem ?
Or what to do to correct this situation ?
Thanks

 

[rayma]

Hi

I had bias problems and now everything is working but I have a major DC offset
of near 250 mv I can't eliminate with the trim pot.

It's more likely that the offset is before R18 (since there is a "unity gain at DC" nfb network),
but you could try replacing capacitor C4.

 

[legarem]

In a service bulletin, R18 and R19 were replaced by jumpers. C4 is a styroflex capacitor. They can go bad ?

 

[legarem]

I made an error
R19 and C4 were omitted in a revision