Can anyone confirm if Mr. Wampler may have left R3 off by accident in the modded schematic?
The link for his mods
http://www.premierguitar.com/articles/mxr-distortion-plus-mods-1
I got this from his book. Let me know if the link doesn't work. I hope it helps
https://www.dropbox.com/s/1inpw9sa19kgcag/Wampler%20DsitP.pdf?dl=0 (https://www.dropbox.com/s/1inpw9sa19kgcag/Wampler%20DsitP.pdf?dl=0)
Instead of using r3 in the stock schematic as a pot to control the filter. He uses r4 in the modded schematic as a pot to control the gain of the negative feedback loop.
That's the best way I can explain it. Someone smarter then me can explain this better.
Thanks everyone. I also got some input from the man himself yesterday while the site was down.