March 16, 2011 10:13 AM   Subscribe

Please help us eliminate an unwanted noise from our home theater.

Apologies in advance for not knowing the technical jargon to effectively communicate my question here.

We have our DVR, PS2 & 3, Wii and PC going through an A/V switch. The audio output goes to a "home theater" receiver with 5 speakers. Some input cables might be HDMI or some-HD-thing I don't know and some are the yellow, red and white guys. Previously, we moved the video output between a projector and an lcd tv. This involved physically unplugging and plugging the output, not an electronic switch.

Everything works great until we plug the output from the switch to the projector, then we get an unbearable humming/buzzing noise.

We've tried different configurations of cords, new cords, a new switch -- the problem is definitely the projector itself but when we go to the projector directly from any of our devices rather than through the switch, we don't get the same noise. The noise only exists when the video output goes to the projector from the switch. The noise exists when the projector is not in use, for example, if we're listening to music from the PC through the switch with audio output to the receiver and the video output going to the projector with the power off. The projector is about 5 years old and the noise only started recently.

Is there some sort of filter or adapter we can use to prevent the noise? And did we cause this by abusing the jacks in some way? (Are these things even still called jacks?)
posted by simbiotic to Technology (7 answers total)
That sounds like a ground loop. Have you tried plugging projector's power cable into the same outlet that feeds the switch?
posted by mhoye at 10:19 AM on March 16, 2011

Response by poster: We have not tried moving the power cords! The projector is across the room from the other things and we were trying to configure everything so that clumsy me would not be tripping over cords.

We will try to rearrange things when the heavy lifters get home from school and work!
posted by simbiotic at 10:34 AM on March 16, 2011

you can always try removing the ground from the projector power cord (if the cord is a removable "IEC" aka "D" plug type there is no hard as a new one can be had for about $2 or free from your local IT guy at work). simply go to the wall end (IE the plug part) and bend the ground pin back and forth until it falls away. generally its connected by a thin little piece of metal and so there should be no remnant but worst case, make sure no jagged or left over metal is exposed outside the end of the plug. be careful and of course YMMV but this is a ground loop and if you have correctly identified the projector as the source this should fix it.
posted by chasles at 10:39 AM on March 16, 2011 [1 favorite]

Ground loop.

Google it and you can find many solutions.

This may require some re-wiring of your home.
posted by BrooksCooper at 10:57 AM on March 16, 2011

Response by poster: Unfortunately, rewiring is not an option.

When I Google ground loop I see "eliminators" and "isolators" for $5-$55. Should we try one of these? Reviews on Amazon seem to say it works. One review says it "badly distorts and attenuates vocals", but we would not be using it for audio output.

Thanks for giving me the language I need to figure this out!
posted by simbiotic at 11:23 AM on March 16, 2011

Seconding what chasles said. You might also be able to find a "ground lift" type adaptor plug at a hardware store. They're usually used for plugging 3-pronged things into the old 2 prong sockets.

Good luck!
posted by luckynerd at 11:48 AM on March 16, 2011

Short term, you can use an extension cord to plug the projector into the same outlet as the other equipment, and that may fix the problem if it is a ground issue. You can also try using a ground lift adapter plug, although by removing the ground, you are exposing yourself to possible problems if there is a short circuit inside the projector (electrocution is not much fun).

On a side note, those ground lift adapter plugs are designed to then have a wire running to a ground connection, they are not actually intended to use in order to completely remove the ground. The ground connection is there for safety, and removing it (using an adapter or breaking off the ground prong) is removing that element of safety should anything go wrong.

If neither of these things fixes the issue, you may have a bad cable running to your projector, which is causing the ground problem. Replacing this cable (HDMI or RCA or whatever else) may solve it, but I would try troubleshooting with the power cables first.
posted by markblasco at 7:40 PM on March 16, 2011

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