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Discussion Starter #1
I recently connected an external amp to my a/v receiver through the receiver's pre-outs and I got what sounds like ground loop hum through the speakers. Before adding the amp, I had no humming issues using just the receiver in my home theatre set-up. After some troubleshooting, I found that:

1) If I disconnect the coax cable (I'm on Rogers cable) going from my splitter to the wall plate where my cable box is connected, the hum is reduced considerably.

2) I have a 30 ft HDMI cable run in the ceiling connecting my projector to my receiver and when I unplug the HDMI to the receiver, this also reduces the hum, albeit only slightly. I wonder whether I ran this cable too close to the coax cable in the ceilng. It's a Blue Jeans HDMI cable recommended specifically for long runs and rated for in-wall use.

From reading here and elsewhere, it seems that an ungrounded or improperly grounded coax cable outside is a common cause of ground loop. I went outside to look at the cable but I can't find anything resembling a ground wire? (see pic here: http://i478.photobucket.com/albums/rr149/highroller54/cable.jpg) Is the grounding perhaps inside the Rogers cable box, which I'm not legally allowed to open?

Can anyone recommend what I try next? I did try another amp which has a ground float switch and turning on the switch eliminated the hum, but very few multi-channel amps have a ground float switch.

Thanks in advance for your help!
 

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You see that black wire that drops down and goes off to the left, it looks like a ground wire. Trace it.

Are you using a surge protector? It may help.

It might be a bad (older) connector on the cable, probably the one behind the wall plate, if there is one.
 

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Discussion Starter #3
Thanks for the reply. I might have trouble tracing that ground wire because I renovated the basement recently so everything is behind drywall except for the electrical panel. Is the ground wire usually grounded to the plumbing stack or the water pipes?

As part of the basement renovations, I had the electrician put in 3 dedicated circuits for my home theatre gear so I wasn't using a surge protector. I did find that plugging the receiver to one circuit and the amp to another decreased the hum, but I can still hear it. I also plugging everything into a power conditioner but that had no effect.
 

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If the incoming coax is not grounded properly at your service entrance it can cause groundloop hum at one extreme and electrocution at the other.

Call your cableco and have them check it!!

PS. Although I live in Winnipeg, I visited my son who moved to Toronto and I was AGHAST at the sloppy, unprofessional Rogers cable installation at his new home. It looked like a scene from Mumbai. The cable was not reinforced at the pole in the lane (it hung from the connector box) and was tossed over/through some tree branches (which sway in the wind and actually snapped the cable during your wind storm), was drooped over the peak of the garage roof (resting on the asphalt shingles), ran to the back of the house where it dropped to the ground in a coil of about 30ft laying on the ground and then entered directly through a hole drilled through the brick bedroom wall (no sealant used) and was connected directly to the back of the cable modem. No ground anywhere!! :eek: It took MANY calls to get it grounded and the holes sealed, but they never did restring the coax. It still runs through the trees and across the garage roof. They did eliminate the 30ft loop laying on the ground.

I must be REALLY spoiled dealing with Shaw.
 

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If you search this forum for "ground loop", you'll find plenty of previous threads on the topic - along with solutions (and unfortunately also workarounds).

The solution is to get the incoming cable signal properly grounded. Also, the various devices in your home theatre should not be plugged into different electrical circuits.

Useful post - FAQs, Search tips, Optimization, etc:

http://www.digitalhome.ca/forum/showthread.php?t=57741
 

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Discussion Starter #8
Thanks for the links and advice! I know it's a common problem, but not knowing where the ground wire goes or what it looks like, I had no idea if I had a grounded cable or not. I just went outside after getting home from work to trace the black wire mentioned by Costa that goes down and to the left and.....it has an unterminated end that doesn't go into the house. It's just sitting there exposed to the outside. If this is in fact the ground cable, then I guess it's not grounded! Is there any way for me to confirm that this is the ground cable? It's a thinner gauge cable than the coax cables (the white one running to the left goes into the basement, the top black one goes to the 2nd floor bedroom, and the bottom black one is the incoming one). I've read that ground wires are grounded to a rod or buried beneath the soil...surely i don't have to dig up my driveway for this?

In any case, I'll give Rogers a call tomorrow to see what they say.
 

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> I might have trouble tracing that ground wire because I renovated the basement recently
> so everything is behind drywall

That ground wire must not be inside. From that cable company junction box must be a ground wire (typically 12 AWG) that is 'less than 3 meters' to earth ground. Same ground used by AC electric, telephone, satellite dish, etc. If all are not grounded there, then hum can exist in various ways inside the building.

If you cannot inspect that ground, then it does not exist. Your post implies you do not even have sufficient grounding for AC elecetric.

From a breaker box must be a typically quarter inch bare copper wire that connects as short as possible to earth ground electrodes.

Your cable must also connect short to that earth ground - if for no other reason, for human safety. Also misunderstood by some: earthing electrodes should be at least 8 or longer.

Surge protectors obviously will do solve a hum. And obviously will not do anything effective if that earth ground is missing.
 

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I visited my son who moved to Toronto and I was AGHAST at the sloppy, unprofessional Rogers cable installation at his new home.
Every time I have moved, way I see it, one way or another, I paid for it so I take it with me...
Before ordering cable service. Remove every cable in the house I'm moving from, take it with me. Remove every cable in the house I'm moving to.
That basically forces them to run new everything in the place, so they're more apt to do a good install job.
 

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Discussion Starter #11
That ground wire must not be inside. From that cable company junction box must be a ground wire (typically 12 AWG) that is 'less than 3 meters' to earth ground. Same ground used by AC electric, telephone, satellite dish, etc. If all are not grounded there, then hum can exist in various ways inside the building.

If you cannot inspect that ground, then it does not exist. Your post implies you do not even have sufficient grounding for AC elecetric.

From a breaker box must be a typically quarter inch bare copper wire that connects as short as possible to earth ground electrodes.

Your cable must also connect short to that earth ground - if for no other reason, for human safety. Also misunderstood by some: earthing electrodes should be at least 8 or longer.

Surge protectors obviously will do solve a hum. And obviously will not do anything effective if that earth ground is missing.
OK, I think I understand what may have happened. I got my electrical service upgraded to 200 amps last year and when they put in the new meter outside, the electrician must have forgotten to ground the cable wire to the new meter/box. I was none the wiser since I didn't even know the cable had to be grounded and the ground loop hum didn't manifest itself until the last few weeks when I introduced an external amp to my HT set-up. So now I suppose I should call the electrician and not Rogers.
 

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I would call Rogers first (basically zero dollars to you, the client) and the electrician next. Ideally, both would be present at the same time.

- Bill H.
 

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Cable company will probably restore the earth ground for free. But you can do it yourself. It is so easy that we have even let teen age kids do it.

Now, if any of those wires were the earth ground, it was not properly installed. See that sharp wire bend? That bend is irrelevant to hum. But the ground is also your entire surge protection. That sharp bend compromises surge protection. The ground from cable to single point electrode also must be as short as possible - ie 'less than 10 feet'. Only some installers and electricians (a clear minority) understand this.

Also inspect their cable on a utility pole (typically where their amplifier is located). If that earth ground is broken (ie due to stray cars or copper recyclers), then have them also restore that ground. Also would do little for hum. But is an important part of your human safety and surge protection system.
 

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Do I need a special tool to open up the hydro meter/box? I realize by even asking this question, it probably means I shouldn't even try messing around with something that could be lethal, but I have to ask :)

And just to make sure I understood you correctly, are you saying that even if I re-attach the ground wire, it does not guarantee that the hum will disappear?

Thanks!
 

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This is cable TV? Why is that box metal? Subscriber interface box is usually plastic to keep rain out.

Coax enters the box. Inside are splitters or a ground block. And the same massive voltage that is on the other end of that wire attached to your TV.

The ground block simply connects your ground wire to the coax shield.

What wire carryies a high voltage electricity into that subscriber interface?
 

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only a lightning strike would carry a high voltage, but if grounded properly, it would be earthed. There is always some chance it would bleed down the cable into the house, but its also important to have a ground block where the coax comes into your house too. Notice how those splitters have a screw hole on them? yeah well its also a good idea to run a ground wire to those too if theyre gonna be in your entrance panel.
 

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only a lightning strike would carry a high voltage
That's not true, depending on your definition of "high voltage"! There are many instances where the coax shield might carry 120/240v (or higher) than your internal household ground.

The incoming coax MUST BE grounded to YOUR service entrance ground system to protect the occupants and equipment in YOUR home.

Caveat Emptor.
 
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