Electrical Hum

criticalmass048September 30, 2006

I posted this message a few months ago, and wanted to try again, since I got only one response.

I watch movies on my computer. I have 2 S-video cables (connected with a coupler), and a 20 ft. 1/8" headphone cable (with a 1/8" - 2 RCA adapter) running from my computer to my DVD burner. I then have component video cables coming out of the DVD recorder going into the tv, and then fiber optic cable connecting the DVD recorder to my amplifier.

What happens is that when I watch a movie on my TV, I have to turn on my DVD recorder first (out of inputs on the TV), then turn on the amplifier. I get an electrical hum, which ranges from "mildly annoying" to "downright maddening" in the background. This probably means I'm turning up the amplifier too loud, but if I turn it down, you can't hear it.

Troubleshooting: When I unplug the headphone cable from my computer, the humming stops. If I plug it into a portable CD player, it's still gone, so therefore it must be coming from the computer. Another member suggested it could be the sound card, but mine is integrated on the motherboard, but how do I test or fix that? The computer is plugged into a surge/battery backup. Could that be it?

Thanks in advance!

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You might have better luck asking this in a computer forum.

If it was me I would just seperate the computer stuff from the tv stuff.

    Bookmark   October 3, 2006 at 8:11AM
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Plug another amplifier (even amplified speakers) into the computer and see if you hear the hum from that.

If yes, it could be the mainboard's onboard sound processor. Most of these are fairly mediocre and shielding is piddle-poor. Shifting cables around or moving other electrically noisy parts (which is to say "just about everything") around inside the computer chassis sometimes helps.

Have you muted all the sound card inputs you're not using?

If all else fails, disable the internal sound processor in the BIOS setup and fit a good quality PCI soundcard. Turtle Beach cards used to be good but I don't know whether they are any more. Maybe Yamaha? It's probably overkill but Echo (echoaudio.com) makes very nice pro-quality sound cards. I can't recommend M-audio; I bought their Audiophile 2496 card a few years back and have regretted it ever since.

If the hum goes away with a different amp, you may just have a ground loop. This is typically a buzzing sound with overtone components rather than a pure 60 Hz hum.

The classic ground loop solution is to fit ground lifters ("cheater" 3-pin to 2-pin adapters) to one or more of the devices (computer, DVD, amplifier).

Also try adding extra ground connections among the chassis, and/or lifting the shield ground at one end of each audio cable.

Getting rid of ground loop hum is often a maddening process of trial and error. Good luck.

    Bookmark   October 12, 2006 at 8:25PM
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