Chip topology

[naca5]

Hi Fellows,

I've in hands a strange amp.
First impression are good but I had a loud background noise and a loud humming when I touch the pot knob.

So I opened it up and.....wires are not isolated meaning signal wires are in contact with ground....

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

 

[DUG]

... a loud humming when I touche the pot.
....

The pot case or pot terminal?

Terminals: normal
Case: Usually used for shielding...normally at signal return potential.

...câbles are not isolated meaning signal cables are in contact with ground....

Looks like RCA connectors are isolated from mounting plate.

Look for a single common ("star) "ground" connection point.

 

[naca5]

Thanks, when i touch pot knob.
What concerns me is that power, ground and signal cables are in contact.
Will try to find the star point

 

[farley]

Are all those various wires bare? Uninsulated?

 

[naca5]

Seems to be...or perhaps varnished ?

 

[farley]

Perhaps re-wire it with proper insulated wires or harvest parts.

 

[naca5]

Perhaps re-wire it with proper insulated wires or harvest parts.

Probably the best thing to do ;-)

 

[nigelwright7557]

Touching the pot shouldn't make it hum as chassis should be earthed.