Touching gain pot makes amp hum.

[cscotto]

Hi,

Well, I was rebuilding my rack. It is based around a recto recording pre and the 2:100. I don't have any ground loops. However, when I touch the gain pot on channel 2, the amp hums loudly. If I touch the gain pot with one hand and then touch either the chassis or the metal part of the rack with my other hand, the hum stops. No other pots on the recto pre produce a hum when they are touched. Could the touch induced hum be caused by a bad gain pot? Thanks in advance.

 

[cradleofflames]

Sounds like a grounding issue on the pot.

 

[cscotto]

Sounds like a grounding issue on the pot.

That is what I thought as well, and that is what it turned out to be. I opened the preamp and attached a wire from the pot to the chassis. With the wire attached, touching the pot did produce the hum. I pulled the pot out and cleared the paint away from the hole in the chassis for the pot and reinstalled the pot. No more hum.

It winds up I had to take it to my amp tech anyway for a switching problem. I told him what I did, and he said it was fine. He said there is so much gain on the channel that he was not surprised it hummed when I touched the pot. In any event, problem solved.

 

[MesaGod666]

Don't touch the gain pot.

:lol: