Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

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RE: You would still have a ground loop.

Posted by Pooge (A) on July 4, 2007 at 14:26:42

In Reply to: You would still have a ground loop. posted by Al Sekela on July 3, 2007 at 15:13:22:

Let me make it clear that I never objected to having two separate power circuits. I haven't been back since my prior mentioned post, but my point in my mentioned post was that IF you had a ground loop, then having two separate circuits would make that loop even larger. You can have ground loop problems in as small a loop as in a single enclosure, so NO you don't need to be large building to have the ground loop created by two circuits matter. The area of the loop is what matters. Even if they are close together, there is some space between them, and it is a lot longer to the circuit breaker box, so the area adds up (length x space between).

My recommendation to plug into the same outlet was merely to aid in diagnosis, in changing the size of the ground loop. However, the proper result could only be obtained by breaking the loop, no matter how large the loop. If there is more than one circuit, the two circuits are "star" grounded at the breaker panel. There should be no other ground connection between the circuits.

Even if you have a ground loop, there must be a coupling mechanism into the signal for it to have an effect. If you have two monoblocks, each with a separate ground back to the breaker box, you get a huge loop if there is a common ground connection between them in the signal lines, which would very likely occur in your preamp, and the coupling would be in the common impedance of the shields. One way to easily diagnosis this is to disconnect ONE of your input to a power amp (after turning everything OFF first!!!) Turn everything on and see if the hum disappears. This should be done after testing the disconnection of any antenna or cable line first, to see if that is the problem.

You don't want to use a cheater plug with the amps!! Although this might break the loop and have the cheated amp grounded through the other amp, it would be through signal lines and pcbs. Any fault might smoke your low level electronics as well as cause a safety hazard.

I would consider using one circuit for one channel, and the other circuit for the other channel, and try to break the ground between the channels in the preamp. Lacking that ability, you're almost resigned to an input transformer on at least one of your amps, which is rather expensive.

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