Modded Marshall Amp Build - Signal when Gain pot is at 0

[Dror520]

Hey guys,

I built a modded Marshall style amp that I kept modding through the years. It has a Plexi and Hi Gain mode switch.
I recently noticed that there's a very low signal still being heard when the gain is at 0.
It's much louder on the Hi Gain mode and It goes away when I turn the master volume to 0.
I've been trying to troubleshoot this, but can't seem to figure it out. Is this normal behavior or is something wrong?

Thanks!

 

[WarHed]

Some pots just dont get all the way to zero, or there's a ground offset on the pot. Nothing out of the ordinary.

 

[glpg80]

Bad ground for the gain pot or the pot wiper needs contact cleaner, or both.

 

[Dror520]

Thanks! I'll try the contact cleaner. The two gain pots (one for each mode) go to the same ground point that's shared with the input jack and the first two stages of the preamp.

 

[schnarf]

If you want to save yourself some guesswork, take the potentiometer out of the circuit and measure the resistance across it when it's turned all the way down. That would show you if it's the potentiometer not going down to 0, or if it's wired wrong.

 

[Exo-metal]

Try dynamite!