Multiple Altec 9440A amplifiers ground loops

[bfish]

I've never had a flaky 9440 volume pot, at least one that cleaning wouldn't cure, but there's always something new.I doubt that's the real culprit especially if more than one has the issue.

I've run up to 3 9440s in a common rack system with none of those issues.

Common ground loop wisdom says it's usually multiple ground paths, but my experience has mainly been from ground paths that had some resistance (usually from poor contact).

Since you eliminated the chassis ground and still have issues, look to the signal ground. Resistance there can have the same effect. Might be as simple as a flaky interconnect or loose/dirty phono jacks.

Good luck!

[rghinton]

You say that you have run up to 3 9440A's in a common rack with none of these issues. Have you used a surround sound processor with a common signal ground to feed 5 channels of the 9440A's with unbalanced cables?

You may have misunderstood what I have found. By removing 2 of the amplifiers, the surround sound processor and DVD player from the rack about 20% of the hum has been eliminated. By lifting the ground from the power cord of both amplifiers 99% of the hum has been eliminated. I have no ground issues operating like this.

In this configuration I now have left, center and right channels with 99% of the hum gone. This sound is very good and clean. Like I said, I think the 1% of hum that is left is probably from the old filter capacitors which I will replace someday.

I do not want to continue to run the amplifiers without the power ground wire but do not know what to do to eliminate this ground loop. Both amplifiers are fed from the same 20A outlet.

[rghinton]

I tried removing the ground shield from one end of each of my signal cables and then running a good ground from the chassis of the processor to the chassis of the amplifier. The hum increased.

My next step is to replace the filter capacitors (9800uf) in one of the amplifiers and also replace the volume controls. Then I will get back to my hum problem. I want to hear one of the amplifiers with 100% of the hum gone and no volume control issues. I have the capacitors ordered and also have the volume controls ordered.

This is going to be a tough problem to fix but I know it will be worth it in the end because I really like the sound of the 9440A amplifiers.