Gren Russian Big Muff - Tone Pot Swing seems off

[killerkev]

Howdy!

I have a Green Russian Muff here that has a problem with the tone pot. It is an original pot that is stamped 150K. The pot was scatching and you could not get that high buzzsaw sound when turned all the way clockwise as you would expect. Infact, it has the lower "bass" sound but when playing with the pot, you can't get much of a tone change. I swapped it out with an Alpha 100K thinking the pot was bad, but to my surprise there was no difference! I checked the resistance range on the new pot and it only measured up to 63K instead of 100K. I unwired it and checked resistance again....normal went to about 95K, wire it back up...low resistance as before. I replaced the four components on the board related to the tone section. No difference.

Anyone have an idea of what could be causing this to occur? All transistor voltages are good and the pedal ROARS but you have no adjustment on the tone.

Below is a link to a schematic guide:
http://www.kitrae.net/music/big_muff_guts.html#Circuit

[kodiakklub]

you could try desoldering the tone pot leads off the board and put in either a jumper wire or a 150K resistor to simulate a pot at full and at zero. that will rule out the pot question.

[Arcane Analog]

Try an audio probe of the section.

[killerkev]

you could try desoldering the tone pot leads off the board and put in either a jumper wire or a 150K resistor to simulate a pot at full and at zero. that will rule out the pot question.

Was thinking about doing this. Why not, might as well and see if anything changes. Seems that something in the circuit is changing the value of the resistance of the pot since it changes when hooked up and then not. Will try tomorrow and post findings.