hum decreases when bass control cranked

[musicfixerupper]

Hi, i just finished an ac30 build and there is a hum that goes away when the bass control is turned all the way up. Could this be a ground loop? I followed the hoffman layout and ground scheme.

[Iannone]

Kind of sounds like a bad ground.  First thing I would suggest is resolver the bass control's ground connection, as it might well be a cold joint.

[archaos]

That indeed sounds like a ground loop.

Where are the signal, AC, DC tied to the ground (& how, i.e. a single point or not) ?