Gainclone hum and digital multimeters.

[Shoog]

I have just got one channel of my gainclone working. I have built it as a single supply so it has input and output blocking caps. I have a loud hum problem. I have tried single star grounding and I have tried double star grounding. In the double configeration I have all the grounds attached to one point, excepting the input grounds and the feedback loop ground.
Here is the strange thing, I attached my digital multimeter on continuity test between the output side of the output blocking cap and ground and the hum goes away. Is this a pointer to the source of the problem and if so what is it.

Shoog

 

[Bricolo]

can you post your amp's shematic?

I don't exactly see how you builded it, and why you use an output cap

 

[Shoog]

It is the standard single supply circuit.

It is the standard single power supply circuit given on the LM1875 data sheet.

Shoog

 

[Bricolo]

maybe you were simply doing a short circuit with your multimeter
that's why you had no more hum

 

[Shoog]

The signal was still there

The signal was still there so I dont think a short circuit would explain it.

Shoog

 

[tiroth]

Hmm...what happens if you tie the output side of the output capacitor to ground via ~100k-1M resistor? This shouldn't make a difference, but maybe a DC ground point at the amplifier side is helping for some reason.

 

[nania]

Shoog

Is the continuity test on your meter also a diode test? Try reversing the leads and do the test the test again. If you return a hum, you defintely have a ground loop problem.