Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: isaac_teller on September 03, 2020, 01:09:48 pm

Title: buzz on volume control only at medium settings
Post by: isaac_teller on September 03, 2020, 01:09:48 pm

Hello. What can be done to stop the buzzing when the volume knob is between 4~8? Other than that the amp is quiet. Thank you.

Title: Re: buzz on volume control only at medium settings
Post by: pdf64 on September 03, 2020, 01:21:58 pm

Have you eliminated it being due to a buzzy tube, ie the stage after the vol control?

Title: Re: buzz on volume control only at medium settings
Post by: tubenit on September 03, 2020, 01:25:24 pm

Sometimes a capacitor going into the pot can leak voltage causing noise.

We might be able to help you more if you shared a schematic and a hi-rez photo of the inside of the amp chassis.

with respect, Tubenit

Title: Re: buzz on volume control only at medium settings
Post by: isaac_teller on September 03, 2020, 01:41:58 pm

I tried several tubes, didn't help. I'll try changing the cap.

Title: Re: buzz on volume control only at medium settings
Post by: PRR on September 03, 2020, 02:39:20 pm

> buzzing when the volume knob is between 4~8?

Crap is leaking into the wire from the pot wiper. Full-up the crap is absorbed by whatever drives the pot; and full-down of course the crap is absorbed by ground. But "in the middle" you have a high impedance to either end. The wire is an effective antenna for any crap in the chassis, especially crap near that wire.

So what does the wiper-wire run near?