Grounding the PI to preamp or power amp?

[randalp3000]

I finished this amp yesterday and it has a pretty bad 60hz hum that's coming from the PI. The hum gets louder when bypassing the cut control or turning up the master. I had the PI grounds and master ground all going to the filter cap for the PI circuit connecting to the power section ground. I have now moved the PI ground to the preamp and it is much better but still a little hum.

So the question, should the PI be grounded to the preamp or the power amp? I labeled the ground scheme on the schematic below and included a picture of the chassis. I did use the amp last night for an hour and a half gig and it sounded quite nice except for the hum.

If you have any ideas or suggestions they would be much appreciated.

thanks
rp

[VacuumVoodoo]

Try grounding your volume pots at ground "A" i.e. at the PI.

[es345]

Looking to the Picture : Where are the two 33uF caps to filter supply D and E?

[VacuumVoodoo]

Unless shadows are playing tricks on me , it looks like they are under the board at the far right.

[randalp3000]

Unless shadows are playing tricks on me , it looks like they are under the board at the far right.

yes they are.....

[Structo]

What is going on with the heater wiring on V1?

[randalp3000]

Last night I lifted the PI ground from point A and connected it to point B, Ch 2 ground and now it's quiet as a mouse.

thanks guys, another lesson learned.

[randalp3000]

What is going on with the heater wiring on V1?

it's an EF86

[Structo]

Ahhh, makes sense now.

Glad you found the problem.