I was playing around with diode placement in your Shaka Braddah circuit and came up with some mods you might be interested in: 1. First I eliminated the diodes from the feedback loop and experimented with shunt diode pairs on the output of the op-amp. In this case the op-amp generates about ~50db of gain, which overdrives the FET pretty severly. This causes a lot of "Marshally" harmonics and distortion. Kind of a "death metal" sound at high gain levels, but at moderate levels it gets more useful (for me) and is an interesting variation. Interestingly enough, in that configuration the circuit is similar to some of the RAT circuits I've seen (high gain op-amp driving a FET through diodes) which may explain the crunchy sound. 2. I left the shunt diodes in and put the diodes back in the feedback loop. This eliminated the clean tone that was coming through simultaneously with dirty tone. This softened the distortion somewhat, less harmonics (and less intermodulation distortion) than without the feedback loop diodes. This sounds more natural to me than the original circuit with the "clean leak". 3. By using an SPDT toggle switch with an "off" position, I can switch between 2 feedback loop diode configurations I like, and none, for that high gain sound. The "cool" sound is good for low drive bluesy stuff. It is extremely touch sensitive. I can back off my neck pickup to 5 and it cleans up nicely with a bright tone that's great for chording. Cranking the guitar volume up adds more distortion and etc. It gets a little buzzy in high drive, but the "warm" sound is nice for higher drive levels. It adds more midrange and the buzz is eliminated. It's touch sensitive at low drive levels too, but not as bright. The "hot" (off) position is the high gain tone described above. 4. Other mods I made - I didn't find the preamp pot useful, so I put a 10k in for full out all the time. The .001 cap in the feedback loop reduces buzz. I sub'ed the .004 cap with a .047 in the tone circuit. This reduced the screechiness and made more of the tone range useful for me. I didn't have a TL072 so I grabbed a TL082 from Radio Shack.