Electrician's advice wanted: safely lifting ground

Yes, both sets of jacks are isolated from the chassis. However, one amp had it's inputs tied to chassis ground so in effect one set of inputs was connected to chassis and one was not.

Either amp, used by itself, is completely quiet.

Yes, it is two paths to ground when one amp has a connection from input to chassis ground and one does not. Because chassis ground is relative to the transformer ground on each amp, and the transformers don't tap at the exact same voltage, so there is a potential created between the two amps. The slight ground current is running from one amp to the other via the input cables. Two paths to ground.

I agree, amp A was creating the potential through that input chassis ground. Lifting the ground on the inputs on amp A did break the loop.

As I said, this does fix the problem safely. I don't mind continuing the discussion in the hope that someone else will find this helpful. Ground loops can be very difficult to solve and I know how much time I spent on this.

This stuff is only fun after you find the solution. :-)

Yes, it is two paths to ground when one amp has a connection from input to chassis ground and one does not. Because chassis ground is relative to the transformer ground on each amp, and the transformers don't tap at the exact same voltage, so there is a potential created between the two amps. The slight ground current is running from one amp to the other via the input cables. Two paths to ground.

Dan_ed,

Then what you are saying amp A had the signal ground connected to the chassis ground, amp B did not. Correct?

Because chassis ground is relative to the transformer ground on each amp, and the transformers don't tap at the exact same voltage, so there is a potential created between the two amps.

the transformers don't tap at the exact same voltage, so there is a potential created between the two amps.

Primary or secondary windings? Can you be more specific....

Over the years I have read threads where guys with mono amps tried everything to rid them selves of a ground loop hum. Only in the end forced to use ground cheaters.

Jea48, our forefathers did not have this fun as their ac was ungrounded. With their stuff in wood boxes, I guess they were safe.

sorry, Jea48. I am not familiar with the specifics of the transformer. But I believe the answer to your question is yes. One amp had signal ground connected to the chassis and one did not.

Coincidentally, I believe that it was work on a pair of new monoblocks that my electronics guy has been doing which gave such a quick solution. He had been struggling with just such ground loop before finding the answer. ;-)

I think it was probably comments from some of those guys using cheater plugs that prompted my starting this thread.

I was born in the 1950's (in the US) and I have many exciting memories of plugging in those loose cords for waffle irons, etc and seeing the insulation blow off the cord in blazing red glory. Those were the days! Space heaters that would set the newspaper on fire. Life used to be exciting.

Speaking of the US and probably for the rest of the world, electrical devices have gotten very wimpy. My main complaint is that 12 volts will not kill anyone so most computer stuff has a transformer brick so the manufacturer can kind of do what he wants to mess things up.

But, there are also now "polarizing" plugs and "grounding" plugs. There were not many vacuum cleaners with ground plugs made in the 1970's. And they consume lots of juice.

The big danger is that there are certain devices like hot plates that are definitely polarized so that they can look like they are off but are still electrified. These are a very big shock hazard and polarizing plugs are necessary.

What has led the massive use of grounding plugs in the past two decades is that there may be a chance that the house has been wired incorrectly and that the polarizing plug will not have the correct hot, neutral configuration.

Consequently, if your house is properly wired the grounding plug has virtually no benefit.

But that being said, I play Devil's Advocate but follow the rules in the end.

For US and Canada the Ebtech HumX is a way to isolate the ground and still follow electrical code.

The trick is that these ground lines can get in all sorts of ways. Through coaxial cable for television (these require grounding at the house drop) and unbalanced interconnect lines.

I do have a question and that is whether RJ-45 (ethernet cable) introduces a ground loop? That is becoming a new possible threat as are HDMI and DVI cables.