120Hz hum when volume pot is off...

[xk49w]

...but not when it is the least bit on.

This is a bass preamp, basically an Alembic F2B with some tweaks. It pretty much is a Fender tone stack between 12A*7 stages. When the volume pot is only slightly off of fully CCW the hum goes away and it is quiet. The wires to the pot do run some distance, maybe six inches.

Is there some sort of inductive loop formed by the wires when the wiper of the volume pot is grounded? If so I suppose I could try some series resistance in the wiper circuit - it would have almost no effect on the volume pot's operation.

[xk49w]

Well, I tried a 10k at the wiper and it seems to have done the trick! Weird one.