"William Sommerwerck" wrote in message
. ..
"Arfa Daily" wrote in message
...

About the only scenario that I can come up with, which might cover all
bases, is if it is a power supply problem. If power to the phono preamp
is
switched, as part of bringing that function on line, then it's possible
that
something in the phono preamp circuitry, is putting noise onto that
supply
line, which may also be used by later stages. If this is the case, then
the
phono preamp will output corresponding noise into the rest of the
amplifier
chain, which will be the component of your noise that *is* controlled by
the
volume control, and also, the noise on the supply rail will cause noise
to
come out of later stages as well, which will be your noise component that
is
*not* controllable by the volume control. A supply rail problem would
also
account for the noise being on both channels.

As a first move, I would try disconnecting the supply rail to the phono
stage. If that stops it, and you're happy with that, then just leave it.
If
you want to try to get a fix, I would be looking at rail decoupling caps,
and transistors.

This is testable without disconnecting the supply rail. Switch the scope
to
AC, and look at the rails while listening to the amp.



This is quite true, but assumes that he has a 'scope, and knows what to be
looking for ...

I went down the route of suggesting just disconnecting the supply to the
phono preamp, because he had implied that he was not particularly interested
in phono functionality, just in stopping the noise. A 'sledgehammer' fix if
you will.

Arfa