PI on power amp or preamp ground?

[JazzGuitarGimp]

Hi All,

Been wondering what the general consensus is on the PI ground connection. When splitting the grounds into a preamp ground and a power amp ground, which is the better connection for the PI?

Thanks!
Lou

[rdjones]

Hi All,

Been wondering what the general consensus is on the PI ground connection. When splitting the grounds into a preamp ground and a power amp ground, which is the better connection for the PI?

Thanks!
Lou

Power amp.
Specifically, the filter ground/negative of the cap that feeds the PI plates.
Also if the amp has NFB the speaker ground should also have a connection here.
In other words treat the PI as part of the overall power amp circuit.

There are several common sense grounding schemes that when done right can work well.
There's no reason that this can't be just as quiet as a global star.

rd

[Firestorm]

I'm on the fence (so is the PI, so to speak). rd makes a reasoned point, but I have occasionally run into presence controls that pick up noisy currents when the ground side is connected to power amp grounds (you only hear it when the presence is all the way off). Aiken also treats the PI ground as part of the preamp (in a two star system), but he also has the screen ground there, which doesn't seem right.

[chief mushroom cloud]

Merlin Blencowe's ground scheme works pretty damn good

[Super_Reverb]

Agree with chief: Merlin's ground scheme works very well. Hoffman has a good scheme too - his basically busses all the preamp grounds into a single point (transformer bolt) where filter, output cathodes and other grounds are tied.

I have used both and had good results.


rob

[C Moore]

Whenever I have worked on the typical BF/SF Fender
I have "always" changed the PI B+ from the preamp caps to the ground of the Power Tube Caps.
I have no way of knowing what doing THAT one mod accomplishes as far as noise is concerned. But it always makes me fell like a corrected a small "flaw" in the Fender layout.
best

[Structo]

From what I understand (and there are many schools of thought here) is that the preamp should ground near the input jack because it is the quietest spot on the chassis.

The PI can ground closer to the power supply filter that feeds it.

Using a Buss Wire, is basically a modified star ground that grounds near the input.