Cmoy Pre-Amp ground hum

[sled108]

This might be a real simple problem, but the threads about ground hums are many, and I've not found a simple answer so far.

What I have here is a Cmoy Pre-Amp powering a TA2024 Amp.

The problem is a ground hum increasing with volume, with no inputs connected and even on the 9V.

This I can easily remove by touching the front face plate.

Am I overlooking a basic grounding rule?
If so, can someone please tell me how to ground this properly?

Thanx...

[Minion]

Do you have your face plate grounded?? if you don"t then that just might fix it , if you Do then I suggest maybe try removeing the ground from the face plate....

Cheers

[theAnonymous1]

Originally posted by Minion
Do you have your face plate grounded?? if you don"t then that just might fix it , if you Do then I suggest maybe try removeing the ground from the face plate....

Cheers

I agree, but to be more specific I would connect the ground from the face plate to the ground directly at the potentiometer.

It's interesting your using what looks like one of the small green ALPS RK097 series pots. I used one of these as a passive pre in a TA2022 amp and also had hum. The hum would disappear if I removed the pot from the front of the chassis or if I grounded the signal at the pot to the chassis. There was no hum at all before I installed the pot and the signal ground was never connected to the chassis.

[Zigis]

I use ALPS RK097 in CMoy amps, wen I touch pot's shaft there is hum. I ground shaft and hum gone.
Solder resistor legs cutoff to pots ground and bend it to front to touch metal part of pot .

[sled108]

I have both removed the Alps from the face plate, and grounded it and the plate to the board's ground and there was no change. The hum is still there... Maybe it's the Amp's PS....From a Canon Printer...
Next, I'll have to work up a 12v battery pack and see how that does.

[theAnonymous1]

If it goes away when you touch the front I doubt it's caused by the amps PS. There has to be some grounding problem inside the pre. Maybe a ground loop between the front and back plate?

[sled108]

Well it seems I've found the answer to my ground hum, and it is kind of stupidly simple...

When I designed this setup, I used (2) 3-Pole 3PDT switches for the input selectors to isolate the grounds. This causes an open ground hum when the switches are both off. Switching one on to an input solves that problem.

The ground hum never exists as long as you're listening to a source.