I worked a long time to get this right, and some magic happened when I boxed it (not sure why, but I think it has to do with grounding and maybe the capacitance of a breadboard.)
Anyway - here is the short demo
with a LONGER DEMO below. I recorded this on my Zoom R24 using the cheap built in mics - from about 9 feet away from the amp - so I do not get a auto-leveling of the audio from my video camera. So - the clean sound is quiet but the pedal is a lot louder - don't turn up your computer:
https://soundcloud.com/paulmotter/demo-diesel-diefet-pedal-from-tagboard-effects<nabble_embed>https://soundcloud.com/paulmotter/demo-diesel-diefet-pedal-from-tagboard-effects</nabble_embed>
By the way - thanks to everyone who helped me - the key seems to have been getting the right grounding on the volume pot - as you guys said.