# HT Hum



## Guest (Dec 1, 2007)

Hello. I'm new to the forums, and looked but could not find a solution to my problem that seemed appropriate, so please be patient with me. I apologize if this is posted in the wrong forum.

Several years ago we had a decent HT professionally installed. No problems until about 2 months ago, when a rather obnoxious hum became audible. Hum level is not proportional to volume setting. No changes to the system have been made, no re-routing of wiring either. The hum comes and goes, and doesn't seem to be associated with any particular household electrical event that I can attribute it to. All power cords are plugged into a monster cable Home Theatre Powerbar 1100. The AV receiver has two signal inputs - a DVD player and an HD cable box. The hum is audible regardless of signal input selected. I tried removing the cable feed into the cablebox, but that didn't reduce the hum level. 

Any advice would be appreciated.


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## Sonnie (Apr 11, 2006)

Hi Fred and welcome to the Shack!

I hate these kinds of things, but they do happen. About the only thing to do is when the hum occurs, start the process of elimination. Disconnect everything but the speakers and start hooking things back up one by one.


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## Guest (Dec 1, 2007)

Sonnie,

Thanks for the prompt reply. I'll try disconnecting and see what happens. Any idea how the hum could have started? I haven't touched the system.


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## Sonnie (Apr 11, 2006)

Short of something malfunctioning in a piece of your equipment, I really don't. Some of our electrical geniuses will probably know. They might be out of pocket on a Friday evening, but will hopefully see this and eventually chime in.


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## brent_s (Feb 26, 2007)

Fred, you don't list your equipment so I'm just shooting in the dark. A transformer, especially the big toroidals found in separate power amplifiers can work their way loose from their mounts over time...mounts are usually screw/bolt and some hot glue if you're lucky. The transformer wants to vibrate and thus hum at the 60hz line frequency. It would certainly fit the symptoms you've described. Some receivers probably have a beefy enough xformer to do the same. You can sometimes identify the source by simply touching the component's case to dampen the vibration.

Try paying attention to what source/surround mode/etc. is active when it happens. Sometimes circuit level connections simply deteriorate over time (weak solder joint or similar), leading to intermittent contacts. For examples, if this happens in a receiver's DSP chip, you might get a hum when using a surround mode, but not straight stereo without any processing applied. Just one example...there are myriad ways this could manifest. 

Good luck!


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## brent_s (Feb 26, 2007)

Another thought before I go beddy-bye. Any chance there are light dimmers or ceiling fans on the circuit with your A/V gear? They're fairly noisy electrically and could possibly inject noise into line if they're slowly failing.


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