My SHO mod is a tone sucker... but why???

[Bishop Vogue]

Hey guys, hoping someone can help me out with a new build.  I love the sound of a SHO, cranked, into an amp with the volume turned down below where I'd normally have it.  I love it so much I thought I'd build a SHO mod, that basically just has the SHO set to high levels and then add a tone pot etc.  Here are the changes I made from the usual SHO:
Added tone control (10KB into a 120n cap to ground)
Used a 4148 and 1N4001 diode instead of 1N4739
Changed the Gain control from 5K C pot to a 500 Ohm linear pot.

Here's a link to my schematic:



When I plug the circuit into a clean amp it sounds great, but with the amp's distortion channel I get that awful tone-sucking crazily-out-of-phasey, makes-you-a-bit-ill sound.  Any idea what might cause this?  It's not the first time I've had this issue (often happens with fuzz pedals).

My troubelshooting (that failed):

Put a Klon buffer in front of it
Put a Klon buffer after it
Disengage Tone control
Put an actual ZVEX SHO into my amp and see if the problem exists with the original circuit (nope, it works fine)

So I'm stumped... any ideas??

[GibsonGM]

What happens if you add a 100k volume pot, after your tone control?  And try turning the SHO level down when you plug into your "red" channel?

You can also try turning down the gain pot (why changed from 5k?), don't run the SHO so hot.

If you run an already clipped signal, or too hot of a signal, into a distortion channel, the signal tends to "fight" itself...it's already a square wave, and it starts to make ugly odd-order harmonics that can sound like icepick sledgehammers in a phaser tossed in a blender....the MAJOR exception to this is a tube amp, which will tend to accept the hot signal more gracefully and sound totally awesome....your amp is not a tube amp, by any chance?

If this is not the problem, then the 10k pot may be interfering with the output impedance of the SHO....making its output impedance higher so the amp has to fight for input, perhaps....not sure of that tho...



Edit:  re-read your post closer...yes, I am stumped like you are, LOL!   Now....the only SHO's I've seen/built have a 9.1V zener from gate to source...and no diodes out front - what is with them?   If you remove them, what happens?    Watch your input level if no zener is present!!