Humming - Home Theater Forum and Systems - HomeTheaterShack.com

 
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post #1 of 9 Old 08-24-13, 07:58 PM Thread Starter
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Humming

Denon 3808 receiver
5.1 set up with in ceiling polk speakers
Cablevision set top box.
Using hdmi in/out all sounds great.
Using rca out from cable box to denon there is an annoying humming sound coming from front speakers. Tried several inputs on denon.
Tried monster rca cables.
No luck.
Any ideas?

Last edited by mechman; 08-24-13 at 09:24 PM. Reason: edited title
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post #2 of 9 Old 08-24-13, 08:08 PM
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Re: Humming

You have removed the cable box from the setup? It could be a bad ground on the incoming cable line.

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post #3 of 9 Old 08-24-13, 08:21 PM Thread Starter
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Thanks 4 response. Cable rca audio out to denon.
Cable box component to tv
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post #4 of 9 Old 08-24-13, 09:04 PM
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Re: Humming

Try disconnecting the coax cable and see if the hum goes away.

Home theater:
Onkyo 805, Yamaha YDP2006EQ, Samson Servo 600 amp
3 EV Sentry 500 monitors across the front, 4 Mission 762i's Surrounds, SVS PB13U sub, Panasonic BDT220, Harmony 1100, Nintendo WiiU
Panasonic PT-AE8000 on a 120" 2,35:1 fixed screen

Living room system:
Sherwood/Newcastle R972, Mission 765's, SVS SBS02's, A/D/S MS3u sub, Yamaha YDG2030EQ
Yamaha KX-393 Tape deck, CDC 805 CD changer, Panasonic BD60, Sony turntable PS-T20
Panasonic TC-P50ST60, HD-PVR & WDTV Live, Harmony 900

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post #5 of 9 Old 08-25-13, 02:34 PM
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Re: Humming

Quote:
kenbola wrote: View Post
Thanks 4 response. Cable rca audio out to denon.
Cable box component to tv
Bad ground is the most probable reason. Problem gets probably worse because you created a ground loop as follows: Box ground to AVR ground via rca cable, AVR to TV ground via HDMI shield, Box to TV via component.
Why don't you send the box's video signal via component through the AVR, too? The TV gets Video via the HDMI-cable as usual.
It seems you do want to hear Audio from the box via your AVR when watching it on TV, don't you? Tehn, this would make sense AND remove the ground loop. Maybe the noise vanishes then, too, though I'm not sure.
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post #6 of 9 Old 08-25-13, 02:35 PM
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Re: Humming

Getting rid of hum can be a trial and error extravaganza.

One thing to check is to ensure that your electrical outlet ground really is going to ground (I've seen it where it wasn't hooked up correctly before...).

Change one thing at a time until the hum goes away. Reinstall whatever it is you changed last and if the hum comes back you've got it nailed. It is an exercise in patience, something I don't have an excess supply of so these are always trying problems. Good luck!

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post #7 of 9 Old 08-27-13, 01:23 AM Thread Starter
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Terrific advice! Thanks. Will troubleshoot and let u know results.
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post #8 of 9 Old 08-27-13, 05:17 AM
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Re: Humming

I agree that the cable box could be the problem. You can get isolation transformers that will break the ground connection. However, you can make your own if you have two 75 ohm to 300 ohm matching transformers like those used on TV antennas. Connect the 300 ohm sides together and then insert the combo into the coax line - easy way to find out if that is the problem. Then go buy the isolation transformer if you want something that looks neater. Otherwise, stay with the home made setup.

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post #9 of 9 Old 09-12-13, 05:23 PM
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Re: Humming

I just saw this thread and thought I'd offer my experience on this issue as it happened to me too. Dont know if you go it cured, but here's a link to my problem thread where I had the same problem, only with a Directv DVR. Some of the steps may work on your problem too.
http://www.hometheatershack.com/foru...ery-c-hum.html

With Directv, you cant use an isolation transformer, but you can with cable.
Hope it helps you, ground loops are a real pain to find and cure.

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