[sdiy] Automatic gain correction for Overdrive

[Don Tillman]

   > Date: Thu, 16 May 2002 07:05:46 -0400
   > From: Dave Magnuson <resfreq at hoohahrecords.com>
   > 
   > At 11:53 AM 5/16/02 +0200, Fortner Florian wrote:
   > >
   > > How can I cope with the strong loudness change in
   > >an overdrive circuit? 
   > 
   > Use a dual (stereo) pot.  When you turn up the overdrive it turns
   > down the output level.

That's the typical approach.  Here's something more unusual:

Another way is to have a circuit with some negative feedback from the
output to the input before the overdrive gain, so the gain control is
within the feedback loop.  It sortof works backwards; increasing the
gain control increases the loop gain, which decreases the level at the
input to the distortion circuit, which reduces the distortion.

An example of this is an alternate "master volume" mod to a Fender
style tube guitar amp where the master volume control is a pot located
between the phase splitter and output tubes of the power amp.  The pot
gradually shorts the push-pull drive signals together making the power
amp much easier to overdrive as well as quieter.  This works because
Fender amps have a feedback loop from the output to the phase splitter
input.

  -- Don

-- 
Don Tillman
Palo Alto, California, USA
don at till.com
http://www.till.com