Stabilizing a Hansen Board amp?

[eric343]

For some reason, when I turn the volume control to the middle third or so, the amp produces a machine-gun like sound in the right or both channels. I assume this is because the opamp is unstable, how could I fix this?

 

[Budgie]

That sounds like a ground loop. If there is a loop pathway in the ground circuit, you can get a low frequency oscillation, in the old days we called it "motor boating" cause it sounds kinda like an outboard motor. Try insulating the input jacks from the chassis and running the input grounds on a wire back to the circuit board.

http://www.epanorama.net/documents/g...oop/index.html

You might find the link helpful in fixing it.

 

[eric343]

It's a plastic chassis, but thanks. I'll go through it for ground loops...

However, the amp also has a bit of a tendency to hiss, so I think there's some instability in addition...