Don Pearce wrote:

On Sun, 20 Mar 2005 13:23:44 +0000, Pooh Bear
wrote:



John Woodgate wrote:

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

Don Pearce wrote...

The mic inputs are discrete - you need to be looking at Q101 and
102 and so on. I'm presuming the line level stuff is quiet enough.

Right, as John and others have also said. Changing the opamp won't
make any difference for the mic preamp stages.

Well, actually it *will* at lower gains where the transistor noise no
longer dominates.

It would make a difference (possibly marginal) to the *noise output* but
not to the mic pre-amp stages themselves, since they don't include any
op-amps.

But they do !

The mic pre consists of a differential long-tailed pair followed by a
differential op-amp configuration to make the signal 'single ended'. The
contribution of the op-amp at low gains normally dominates the noise output
of the mic pre.

Yes, but he only has the noise problem at high gain settings.

I was talking in general terms ( and pointing out that the mic pre uses an
op-amp ). No point in having noise when you needn't.


Graham