I read in sci.electronics.design that wrote (in
) about 'Reducing hiss
by changing op-amps ?', on Sat, 19 Mar 2005:

I have an audio mixing desk from the 80's that is a bit 'hissy' (i.e.
background noise with no inputs). Would I be able to reduce this by
replacing the op-amp ICs with lower noise versions ? ...or is this sort
of noise nothing to do with the op-amps ?

It's to do with almost all aspects of the design. If you replace the op-
amps with more modern ones, they will probably be faster as well as
lower noise, so there may be stability issues. In addition, you may get
no improvement because the circuit impedances are not optimum for the
new op-amps.

Note that the most critical circuit for noise, the mic amplifier, uses
discrete transistors. You could get lower noise with a modern design,
but such a design is by no means easy.

The overall design has, by modern standards, far too many op-amps in the
signal path.
--
Regards, John Woodgate, OOO - Own Opinions Only.
There are two sides to every question, except
'What is a Moebius strip?'
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk