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Electrical Interference Humming Craziness!  

post #1 of 13
Thread Starter 
Okay--Here's a problem for some creative electrical engineering types out there. Please forgive the length of the post.

I have an Acurus Pre-Amp, and Amplifier combination for my home theater set-up. It sounds great, BUT when I plug the amplifier into the outlet closest to the equipment, I get a fairly loud buzzing sound through the speakers. My first line of attack was to get a Monster Cable Surge Protector/Line conditioner, but that did not eliminate the buzz. I can plug the amp into an outlet on the other side of the room with a big extension cord, and there is no buzz then. The outlet that I want to use was originally on the same circuit breaker as the overhead lights, which have a dimmer switch attached, and when I dimmed the lights up and down, the buzzing changed, so then I thought that maybe the dimmer was the culprit. However, I can turn the lights off completely and the buzzing is still there. Still, I figured, to be safe, why not run a dedicated line for the home theater equipment directly to my electrical panel--that should cure it--or so I thought. I had my electrician wire the outlet directly to it's own dedicated breaker on the panel, but the buzzing is STILL THERE. Also, dimming the lights will still change the sound of the buzz, even though the lights are on a different circuit now. It can't be the lights, though, causing the buzz, because I can turn off the breaker to the lights and the buzzing is STILL THERE.

Now, I was fiddling with plugging in the amp to different outlets and here's where it gets really screwy-- The outlet I have been using (with a nice orange extension cord across the room) has four receptacles. If I plug the amp into either of the two left receptacles, no buzz. If I plug the amp ALONE into either of the two right receptacles, then there is a buzz. BUT, if I plug the amp and my television into the two right receptacles (or both into one of the right receptacles through a surge protector) then no buzz. This last bit seems to make NO sense to me, but I am no electrical engineer, just a guy who knows enough about wiring to be dangerous.

Any thoughts out there?

post #2 of 13
Hi Dan, just a few questions.
1. Do you plug everything into the new dedicated circuit or just the amp?
2. Is the cable still attached to the TV when you plugged it in the outlet across the room?
3. Are there any other dimmers in the house or halogen lights that have 2 or 3 settings?
4. Is the four receptacle outlet(which I assume is 2 duplex outlets in one box)fed by a 2 pole breaker, two separate breakers or one breaker?
More than likely the four outlets are fed by a three wire and each side of the plugs are on a separate phase.
The first thing I would do is check to see if the TV cable has been bonded properly, then disconnect the wires on the dimmer itself[some dimmers will still cause buzzing when the breaker is off and/or if not grounded at the switch box (some current going from neutral to ground directly or going through the disconnected hot through the lights to ground)]sounds like the ground of the dimmer isn't connected, next get the electrician to move the breaker to the other phase.
That's all I can think of right now without more info.

[This message has been edited by pfokkema (edited 05-10-2001).]
post #3 of 13
Thread Starter 

Thanks for the response. As to your questions...

1. I have tried plugging everything into the dedicated circuit and just the amp alone. I have tried putting the amp on the Monster Cable power supply or separately directly into the outlet, and the results don't change.

2. The cable is attached to the TV when I plug it in with the Amp. I don't know about bonding cable, but it is good quality RG-6 cable and my same electrician ran the cable to the room with the home theater.

3. There are MANY other dimmers in the house, and some halogen lights too. In the home theater room, itself, there are 3 dimmers, two of them set up as one-way switches for various overhead lighting and the third set up as a three-way switch with a hall light. The light switch that seems to affect the buzz the most is one of the one-way switches, and it has only regular incandescent light bulbs, attached to it. All three switches are those fancy (Maestro by Lutron, I think?) dimmers that bring the lights up and and down slowly to a preset level.

4. I am not sure which circuit the four receptacle outlet is on--or if it is on one or two different breakers--I don't know about phases. The electrician thought that one of my phases, I think, could be causing the buzz and he would need to connect the dedicated outlet to the other phase, but he hasn't come by to try that yet. He tried to explain how I could check to see if the dimmers and the dedicated outlet were on the same phase by looking at the panel, but I am unsure.

I checked to make sure the dimmer was grounded (I had installed it myself). Interestingly, and maybe totally unrelated, the dimmer that affects the buzz the most (although all three affect it a little) was hot to the touch when I took off the switchplate cover to make sure it was grounded. I may replace the switch because I am concerned about the heat, but I thought that turning off the breaker for the lights should end any interference from the dimmer--maybe not?
post #4 of 13
Just put those little gray "cheater" adapters on every 3 pronged connector in your system. These are the little gray things you buy at Home Depot that are supposed to convert a 3-way appliance to a 2-way outlet with a little green wire coming out of them that is supposed to connect to the screw in the middle of the faceplate. DON'T connect the green wire, just leave it hanging. You have a classic "ground loop" between the 2 separate grounds. It is OK to have one ground point, but with 2 or more, you're going to have problems. Your Cable TV connection is usually the cause, it is on a separate ground from the rest of the house, and causes no end of hum problems.

Bob Smith
post #5 of 13
DO NOT use a 2 wire adapter and leave the green tail unattached. This is a safety feature for cords with a 3 prong male end. Without the wire attached, if there is a short circuit in the component, the circuit breaker or fuse can't operate, and the equipment will become live, presenting a dangerous and possibly fatal shock hazard.
As far as the cable ground, National elec. code requires that it be bonded to the electric service ground, not separate. Cable companies are notorious for ignoring this and driving their own separate ground.
post #6 of 13
Thread Starter 
Thanks-- I don't think it is a ground loop interference. The Monster Cable Power supply is supposed to isolate the several components on the power strip, and in any event, I get the buzz even when the amp alone is plugged into the dedicated circuit.

As to the grounding of my cable line, actually it IS bonded to the grounding of my electrical system. (My satelite dish is not, but the buzzing has been going on long before my satelite was installed).
post #7 of 13
Dan, when just the amp is plugged into the dedicated circuit is there any other cables connected to it besides the speakers?
post #8 of 13
Thread Starter 
Yes-the Pre-Amp is connected to the amp's five inputs, and the five speakers are connected too (buzz comes from all five speakers).

post #9 of 13
Dear Bobs,
Use a "cheater plug" and you risk shock and fire hazards, but maybe no hum.
post #10 of 13
Use the cheater plug only long enough to verify that the problem goes away. If it does you have confirmed the ground loop theory, if not you have to keep troubleshooting. Do NOT make the cheater plug your permanent solution.
post #11 of 13
I agree with Bob Smith. Use a cheater plug on all of your 3 prong plugs and you will get rid of your ground fault. The case of these devices will no longer be referenced to Earth Ground.
post #12 of 13
This may not be the answer, but to change the "phase" of the circuit go to the electrical panel (only if you are comfortable working in there) and switch the wire from the breaker that is humming to the one over or under it. ONLY IF ITS THE SAME AMPERAGE like 20 amp 15 amp. or you may find it easier to just switch the whole breaker with the one over it or under it, so you don`t have to unscrew the wire from the breaker. Every other breaker from top to bottom is a phase. This way you don`t have to wait for your electrician for that problem at least.
Do you have a ground rod and everything is properly grounded?
post #13 of 13
Thread Starter 
Thanks for all the responses. I haven't had a chance to try a cheater plug yet (I don't love that as a solution anyway), but I did do some further digging around the house, the dimmer switches and the electrical panel.

First, I totally disconnected the three dimmers (first turning off the circuit)and the buzz was still there, so even though the dimmers can change the sound of the buzz, I don't think they are the cause. Then I checked the outlet that does work without buzzing. Interestingly, it is a 4-outlet plug and the two sides are on two different circuits--with the right half having a buzz and the left half not. I think this lends weight to the phase problem. I am not so wild about opening up the panel, however, so I may have to wait for my electrician to change the phase of the dedicated circuit.

Question, however--as to ground loop interference. From my limited understanding of what causes it, I would think I would need at least two grounding rods in the ground with electrical connections to cause the difference in potentials. I now have two different grounding rods, but the second rod is new (for the satelite dish) and the buzzing was happening even before I got the satelite dish.

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