PWM on complex audio signals

[DCMagnuson at aol.com]

Hi List,

I came across a circuit for adding PWM distortion to a guitar signal.  The 
schematic is located at: http://www.cs.ucl.ac.uk/students/M.Rogers/pwm.html

I'm assuming this is simply a wave shaper.  The circuit was redrawn to use a 
single 9v supply, but I'd be interested in seeing the bipolar version.  This 
schematic is a modified version of a circuit from "The Mix" magazine (not 
sure which issue).

Does anyone know where I could find a copy of the bipolar version?  Tony 
Allgood and Oliver Batz are listed as helping with the 9v design.  Do you 
still have copies of the originals?

Has anyone built this circuit or something similar?  I would specifically 
like to try it on audio signals from my digital synths / sampler / drum 
machines.  What will something like this sound like?

Thanks in advance

Dave Magnuson