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In Reply to: RE: thanks guys posted by DC STEVE on June 21, 2007 at 21:27:41
It sounds like the surge unit (cheap) is leaking on both the neutral and earth. If that it the case check for excessive leakage on the earth (the number one culprit for hum). I'm sure the polarity is fine. Unless the guy is a moran, it's pretty hard to screw up the polarity...especially for a pro who has done this more than once.
If it is the surge unit, there are three ways to fix it. One, rip out the surge unit and replace it with a quality magnetic breaker. Two, lift the ground at the outlet (not advised...but it is what the surge circuit believes you are going to do). Three, lift the ground by using either isolated or split phase (balanced) transformer on all your a/v circuits.
To clarify about lifting the ground at the outlet...if you have a copper cold water pipe near the a/v duplex, you could run a 12ga insulated ground to the pipe and have a good grounding set up. Take all of you dedicated lines and star ground them at the pipe clamp. Just make sure you scrub the pipe surface clean with Caig Progold 100% solution before installinth the ground. Also make sure the clamp is solid copper and not something cheap like zinc if you want a solid ground.
Alan
Follow Ups:
The notion of a separate ground for the audio circuits has been discussed before, but is worth repeating in this context.
The AC "ground" in USA-type wiring is a safety system. It is a separate conductor in each circuit that is tied to the neutral at the entrance panel. Its purpose is to carry fault current arising from a short from hot to exposed metal on the attached equipment until the circuit breaker opens, without allowing a lethal voltage to appear on the exposed metal. This means the resistance of the safety wiring has to be low.
By connecting the audio outlet ground terminal to a water pipe or other independent earth electrode, the safety circuit has the resistance of the earth between the independent electrode and the ground electrode to which the neutral is connected inserted into it. Fault current passing through this extra resistance could cause a lethal voltage to develop on the exposed metal of the faulty equipment and the circuit breaker might not even open. This could cause a fire.
The neutral and "ground" wires are all connected to earth at the service entrance to help protect against lightning-induced common-mode surges. If there should be a nearby lighting strike with a separate audio earth connection, the lateral currents that flow through the earth between the two electrodes can cause a very high voltage to develop between the neutral (tied to earth at the service entrance) and "ground" (tied to earth by the independent electrode) at the audio outlet. The outlet will flash over at about 6000 volts, but the equipment may be destroyed and set on fire in the process.
Agreed Al...which is why I told him not to pursue this option...instead I told him to lift the neutral using a isolation transformer.
Alan
One more clarification....the best option for you if you decide to keep the surge is to isolate your components with a transformer...either unbalanced or balanced is fine. This is the safest way to lift the neutral in order to stop the hum and remain grounded to the house.
Alan
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