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Possible ground loop problem


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12 replies to this topic

#1 of 13 ChrisConklin

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Posted August 09 2003 - 11:57 AM

I get a hum in my speakers and sub when i select an analog source on my receiver, and by unplugging the cable from the back of my TV the buzzing goes away. I have a cable modem so from my main cable outlet i have a splitter that goes to the TV. Is there anything i can try to fix this problem?

#2 of 13 Glenn Overholt

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Posted August 09 2003 - 03:10 PM

The first thing that I would check would be to see if the cable company grounded their setup to your house ground.

This is assuming that you know that the coax inside does not have any shorts in it.

Glenn

#3 of 13 ChrisConklin

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Posted August 10 2003 - 04:57 AM

Well i have no idea how to check if the company grounded it, i'm in an apartment so i'd have no idea where to check. The coax was working perfectly until i hooked up my receiver. Would it do me any good to buy a better shielded coax, or get one of those power strips that has a coax in and out on it?

#4 of 13 Glenn Overholt

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Posted August 10 2003 - 10:14 AM

No. it wouldn't. I was in an apartment complex and when they converted over to digital, they forgot to ground it completly. Very sad.

I take it that you just got the cable modem, but didn't think to try out the receiver while they were still there. If this is a new install, then I'd just call and tell them that you're getting a humming sound now that you were not getting before, and think that it should be checked out.

I would question what you have plugged into the analog section of your receiver, though. Disconnecting anything there doesn't change the hum?

Glenn

#5 of 13 ChrisConklin

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Posted August 10 2003 - 01:40 PM

Actually i've had my cable modem for a while, it was getting my receiver that was recent.

#6 of 13 Glenn Overholt

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Posted August 10 2003 - 03:00 PM

Ouch! Ok, that's a little different, I think. I'd get a piece of wire (It doesn't have to be very thick, maybe some extra speaker wire) remove the insulation from both ends. Stick one into the ground terminal of your receiver, and wrap the other end around the screw that is in the center of your wall plate (Just unscrew it a couple of turns, wrap the wire and tighten it up).

I think that your only other option would be to start wiggling or swapping cables out. Unplug everything from your receiver's analog section, try out the radio if you have one, and plug items back in, one by one. Does the CATV go into a VCR or cable box? Can you remove the coax line from your TV and use component lines intead?

Glenn

#7 of 13 ChrisConklin

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Posted August 11 2003 - 03:11 AM

My TV cable goes straight from the wall into the back of my TV, then i have audio analog out from my TV to my receiver. When i listen to the TV through the receiver i get a slight hum in the center channel. When i switch to CD (which is actually my computer hooked to the receiver through a mixer) i get a real bad hum from the sub. My room is small so my TV and receiver are close to my computer. Simply unplugging the TV coax cable from the back of the TV solves the humming in CD mode and the vertical lines i'm getting on my screen...of course i just can't watch cable TV then.

#8 of 13 Glenn Overholt

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Posted August 11 2003 - 04:43 AM

I can see your frustration now. Does it do this if your PC is off? (Not a solution - just a thought).

Can you run that wire (that you din't run from the ground of your receiver to the wall socket) instead from the receiver to the cATV splitter?

Just trying to eliminate loops here. The splitters usually have a sheet metal screw in them for grounding anyway. I hope that does it.

Glenn

#9 of 13 ChrisConklin

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Posted August 11 2003 - 09:18 AM

The problem isn't solved when i turn my computer off...but if i unplug the power strip its connected to the problem is also solved. I connected the splitter to a screw on the cable socket...but that didn't work, i guess its not grounded, i'll try connecting a wire to an outlet or try going to radio shack and getting their A/V power strip w/ coax in/out just to see if it does do anything.

#10 of 13 Bill Kane

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Posted August 11 2003 - 09:45 AM

Yes, sometimes using the coax F-terminals on a surge protector is a quick-and-easy method -- this will "bond" the cable coax separate ground (or lack thereof) with the primary A/V house ground, and tend to mitigate the ground loop.

The incoming coax goes into the surge terminals and out to the splitter. Best use a splitter rated for at least 1GHz or higher for quality and lesser dB loss.

Also you ask around for $20 type ground isolator at AV stores and shops. Someone also may suggest the RS 300ohm-to-75ohm back to back isolator...

#11 of 13 Ted Lee

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Posted August 11 2003 - 11:29 AM

although i've never tried it, i've also heard that the rat-shack doo-hicky is supposed to work pretty well. i remember suggesting it on a different thread and the guy said it solved his problem completely...
 

#12 of 13 ChrisConklin

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Posted August 12 2003 - 11:13 AM

Well tried the Rat Shack doo-hicky and while it reduced the hum by maybe .0005% it ADDED picture distortion, so that's going back to the store in the morning and picking up the power strip instead.

Edit: Ok i didn't get the inline coaxial surge protector but got the 75-ohm interference filter.

#13 of 13 Steve Lucas

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Posted August 13 2003 - 02:26 PM

Just a thought, I have a cable modem too, and when they installed mine, they split the cable. One side going to the cable modem and the other feeding all the TV's in my house. The line with the TV's has a filter to eliminate all the digital signal going to and from the modem. Could it be your tv cable is either unfiltered, or that since your computer is connnected to your amp and your amp to your tv, that you are getting some kind of digital feedback or interference from the cable?

Steve
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