tone control in feedback loop

[sangram]

Hi

In upgrading and refurbishing vintage amplifiers, I've come across a number of beasts where the tone control is included in the feedback loop of the power amplifier - usually they control pots are all the way in the front of the amp and the actual circuitry is quite a distance away, sometime more than half a dozen inches. Obviously a cost-saving measure...

On occasion I would like to remove this completely, disabling the tone control and shortening the feedback loop with attendant benefits in S/N and distortion. In such a case, would it be possible to compute gain requirements from the power/voltage output and input sensitivity and just replace the network entirely with two resistors and a cap (if needed)? Or are there any other gotchas? Additional compensation?

Here is a recent example: A Harman Kardon 6300:

[jaycee]

I am wondering this myself - my Marantz PM-35 has a similar arrangement. I plan to get rid of it and build a "proper" preamp with opamps.