Very noisy master volume pot

[EETStudent]

I started troubleshooting my noisy preamp today, and right now im at the very basics. I ran the input into the first gain stage, and that straight into my phase inverter. Got the results i was expecting. Not noisy, but not a terrribly strong signal. Then, I put the master volume between the triode stage and the phase inverter, and it was VERY noisy then. The pot was grounded(ran a jumper cable straight to chassis), the other leg was coming off of the plate, and the wiper to phase inverter. What made such a huge difference here?

[Enzo]

Sounds like you didn't also put a cap between the plate and the volume control. Is there something like 100v or 200v across the pot now? That would make any pot very noisy. Pots don't like DC voltage. Also, the wiper would also have DC on it, which would vary with the setting, and that would possibly get into the phase inverter unless it had a cap at its input.

[EETStudent]

yea Enzo that worked. However, i just cannot get the gain control to function properly and i cant get the volume and gain knobs to stop sounding very scratchy when adjusted, even though their brand new pots. I dont get it, wiring up these two pots seems so easy. With the gain control, it feels like i get maximum gain when have it at 3, and then it gradually declines after that. But from 0-2 it almost functions like it should, by gradually rising. I dont know, im confused.

[Enzo]

Whe clean pots scratch, it is usually from DC across them - check with your meter.

If they just don't seem to work like volume controls, I'd be thinking they are miswired.

[EETStudent]

When I measured across the two outisde legs, it was 2Vdc. From each leg to wiper it was 5V. is this causing the scratchiness? if so, how do you get rid of that?

[Enzo]

The wiper is putting the voltage into the pot. Is there a cap between the phase inverter and the wiper? Should be.