Input ground on a PP amp

[angelodp]

Hi, I have isolated the input on a current PP amp with those nice washers. The closest ground point for that jack is the same spot as the V1 cathode ground. Good or bad idea? I ask as the move has helped the slight hum slightly. I could create a new ground point for that separate from the cathode ground.

A

[pompeiisneaks]

Hi, I have isolated the input on a current PP amp with those nice washers. The closest ground point for that jack is the same spot as the V1 cathode ground. Good or bad idea? I ask as the move has helped the slight hum slightly. I could create a new ground point for that separate from the cathode ground.

A

anything that is preamp level can be at the same potential ground w/o any problems, usually the phase inverter is best to start separation.

~Phil

[angelodp]

Copy thanks.

[echuta13]

Take a look at the Monkeymatic amp for a good example of an localized pre-amp ground scheme. https://tubeamparchive.com/viewtopic.php?f=6&t=33878

[R.G.]

There are two places that are good ideas theoretically. These are the chassis star ground point and the ground side of the grid leak resistor for the input tube. The chassis star ground point forces there to be no "sewer ground" current in the input lead to be amplified, and the grid leak resistor approach ignores the ground current stuff in favor of making the input be quasi-differential, kinda.

As with all ground problems, you can wind up with less hum overall by accidentally introducing more, but cancelling hum signals. This leads to eternally chasing hum sources as they cancel and un-cancel each other.