Op-amp Big Muff JHS Pumpkin Patch Mod

[classic.evil]

Hey there, does someone has details about the Pumpkin Patch mods JHS did with the Op-amp Big Muff?

Thank you!

 

[Bricksnbeatles]

Mods control is probably just the AMZ muff tone stack mod. Not sure what the gate switch is tho

 

[jwin615]

Try futzing with R11(in this schem)

It will misbias the 741 stage. Try omitting it completely and a 1meg pot wired as a variable resistor in series with say a 250k resistor. Find cumulative resistance values that work.

You'll basically add more/less DC offset to the AC signal, forcing it into one rail. Once the AC signal is operating only on one side of the bias, you should get a gating effect as it just looks like DC at that point.
I think. It's early

 

[drgonzo1969]

Here is a gut shot of mine.

 

[Robert]

Can you see the value on that 9mm pot?

I have a stock one I can trace for a schematic.

 

[drgonzo1969]

That’s the only marking I can see other than the alpha logo on back. I tried to get the knob off just now so I could take the pot out but half the flat head screw insert broke off.

 

[classic.evil]

Here is a gut shot of mine.

Thank you very much!
So this actually isn't a biasing mod in the feedback loop. It's a clipping mod. 1. Stock. 2. asymmetrical Silicone/blank and 3. asymmetrical Si/LED
I really thought it was a bias mod.

 

[jwin615]

Looks like R19 was removed, maybe the pot is replacing it?

 

[classic.evil]

Looks like R19 was removed, maybe the pot is replacing it?

Yeah, I think it's the AMZ presence control. In the case of the attached schematic R15 us replaced by a 3k3 resistor and a 25k pot.