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In the Forum: Audio Discussions
In the Thread: It’s mad, mad, mad... electricity.
Post Subject: Is this common-mode voltage ?Posted by jessie.dazzle on: 8/27/2008
In my case, I have not observed any fluctuations in sound quality other than those resulting from my own state of fatigue (maybe they are doing something right with power generation/distribution over here... I don't see many complaints coming from outside the U.S... Could this be a clue?), but I do have a question :
I think it is the result of what is called "common-mode voltage".
When I disconnect the ground lead from the dedicated lines (ground lead located near the components, not at the circuit breaker end), there is a presence of voltage that leaks out onto the metal boxes housing the outlets, and to the grounding lugs on the chassis of the components. It is of a level such that one cannot maintain bodily contact for more than an instant. With ground lifted, there is a buzz in the sound coming from the horns. Connecting the ground lead results in a small spark, but immediately takes care of the problem (both the buzz as well as the not-so-small shock when touching the metal parts). The path to the components is really direct... There is a very fat 2-conductor cable that goes from where the main line enters the building, straight to the big main switch on the circuit breaker panel with no interruptions... From there I wired things so as to bypass the sort of intermediate circuit breakers (recently made mandatory over here), going instead directly to the dedicated circuit breakers, which in turn feed 5 runs of 2-conductor cable, about 30 ft long, terminating at the outlets near the components... Still no ground. It is at the component end that I finally do ground things to an iron beam in the foundation and wall. I have not bothered pulling out the oscilloscope, because with the ground connected I seem to have very constant sound quality. Still, I don't like knowing that I am having to kill such a strong mystery voltage.
So my question : Is this what is called "common-mode voltage"? Should I be concerned that it is so high in my case?
I had the same issue, but not so strong, in one of my previous apartments here where there were no dedicated lines.
Thanks for any thoughts,
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