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Ground Loop issue

post #1 of 16
Thread Starter 
I have been reading about Ground Loops, and have tried to troubleshoot to success, and am having an issue I would like some input on.

I replaced a 2 prong Yamaha subwoofer with a 3 prong HSU VTF-2 Subwoofer. When I did this I had a horrible hum. I diagnosed it down to a ground loop, and a lot of it was coming from my coax cable. I had comcast come out and ground it out, but I still have about 10% of the noise.

I purchased a ground loop isolator http://r.ebay.com/bLFqWO and it also reduced the sound somewhat, but I still have a hum.

I can use a cheater plug, and that reduces it completely, but I just don't feel wonderful about using one.

Thoughts?

1. Is the isolator I purchased such a crappy one, that I should buy a better one?
2. Should I try a directional cable? (as described here) http://oreilly.com/pub/h/4241
3. Blue Jeans cable suggested that if I rewired my the cable run with their LC-1 cable, that that should fix it?

Is there anything else you guys need to know?

Thanks a ton in advance.
Best,
Geoff
post #2 of 16
Quote:
Originally Posted by extotherule View Post

1. Is the isolator I purchased such a crappy one, that I should buy a better one?
Maybe, but only as a last resort.
Quote:
2. Should I try a directional cable?
There's no such thing. The link shows a cable with the shield connected only at one end. The spade lug is superfluous, and the arrow is marketing piffle. You can make your own cable with the shield connected at one end only and give it a try.
Quote:
3. Blue Jeans cable suggested that if I rewired my the cable run with their LC-1 cable, that that should fix it?
After reading their description of it my opinion of Blue Jeans went way, way down.
Quote:
Is there anything else you guys need to know?
is your TV cable transformer isolated? That's the number one source of ground loop noise in HT systems. Cable systems tend to be clueless in this respect.
post #3 of 16
Quote:
Originally Posted by extotherule View Post

I purchased a ground loop isolator http://r.ebay.com/bLFqWO and it also reduced the sound somewhat, but I still have a hum.

I can use a cheater plug, and that reduces it completely, but I just don't feel wonderful about using one.

Thoughts?

This is the isolator I purchased to use when I need to temporarily isolate a ground loop situation. Pricey, but it does a killer job.
post #4 of 16
Quote:
Originally Posted by extotherule View Post

I have been reading about Ground Loops, and have tried to troubleshoot to success, and am having an issue I would like some input on.

I replaced a 2 prong Yamaha subwoofer with a 3 prong HSU VTF-2 Subwoofer. When I did this I had a horrible hum. I diagnosed it down to a ground loop, and a lot of it was coming from my coax cable. I had comcast come out and ground it out, but I still have about 10% of the noise.


Is there anything else you guys need to know?

Thanks a ton in advance.
Best,
Geoff



I use this item on my antenna feed as a supplement to the cable ground:

http://www.amazon.com/gp/product/B0017I3K9M/ref=oh_details_o03_s00_i01?ie=UTF8&psc=1
post #5 of 16
Thread Starter 
Quote:
Originally Posted by BeeMan458 View Post

This is the isolator I purchased to use when I need to temporarily isolate a ground loop situation. Pricey, but it does a killer job.

Thanks I will take a look at that. It is from amazon with prime, so worst case if it doesn't work I can shoot it back.
post #6 of 16
Quote:
Originally Posted by extotherule View Post

Thanks I will take a look at that. It is from amazon with prime, so worst case if it doesn't work I can shoot it back.
Before you do, a simple experiment: disconnect the TV cable. If the hum goes away it's the source. If it doesn't, it isn't.
post #7 of 16
Thread Starter 
Quote:
Originally Posted by Bill Fitzmaurice View Post

Before you do, a simple experiment: disconnect the TV cable. If the hum goes away it's the source. If it doesn't, it isn't.

Thanks Bill. I am sorry I didn't mention that I already did this and had my cable company come out to ground it and that hum has been removed that was coming from the coax.
post #8 of 16
Quote:
Originally Posted by extotherule View Post

Thanks Bill. I am sorry I didn't mention that I already did this and had my cable company come out to ground it and that hum has been removed that was coming from the coax.
Do the experiment anyway. Cable companies don't know diddly about audio, they only know about complying with code. The trouble is that the code doesn't know diddly about audio either, and the practice of grounding the cable at or near the service entrance doesn't stop ground loops. Maybe they fixed it, maybe not. If they did then you don't need to fix it again.
post #9 of 16
Thread Starter 
Quote:
Originally Posted by Bill Fitzmaurice View Post

Do the experiment anyway. Cable companies don't know diddly about audio, they only know about complying with code. The trouble is that the code doesn't know diddly about audio either, and the practice of grounding the cable at or near the service entrance doesn't stop ground loops. Maybe they fixed it, maybe not. If they did then you don't need to fix it again.

I will try it again Bill.
I verified most of the hum was coming from the cable, and that is why I called Comcast.
I contacted the cable company. and they sent out a guy.
He grounded inside, it didn't help, he grounded at 2 points outside. We retested, and the ground loop/hum from the coax attached or not had fully dissapeared.
I stood over his shoulder the whole time to make sure it was done correctly.
post #10 of 16
Disconnect cable TV coax as Bill suggested. Also, did he change the F Connector at the pole? The ground (shield) can get very corroded. The corrosion can sometimes travel down inside the coax which would require it being replaced.
post #11 of 16
Quote:
Originally Posted by extotherule View Post

I contacted the cable company. and they sent out a guy.
He grounded inside, it didn't help, he grounded at 2 points outside.
Like I said, they don't know diddly. Ground loops aren't caused by poor grounds, they're caused by good grounds, just too many of them. The cure is to remove one of the ground paths via transformer isolation. That's very expensive with the AC ground, requiring a high voltage high current capacity balanced 55v-0-55v transformer. It's cheap on the TV cable, requiring a low voltage low current capacity transformer. But again, before fixing it make sure that's the problem.
post #12 of 16
I wonder if everything was ran thru a power console so that you won't have multiple device competing for the earth ground would fix things. I use two of them and it removed the problems from running multiple source via different outlets.
post #13 of 16
Quote:
Originally Posted by derrickdj1 View Post

I wonder if everything was ran thru a power console so that you won't have multiple device competing for the earth ground would fix things. I use two of them and it removed the problems from running multiple source via different outlets.
The severity of ground loop noise is determined by the square of the combined distance of the various ground wires connecting the various devices. Using a single power connection can reduce the length of those ground connections, and if it does so it will help. The TV cable tends to be the worst culprit because it's typically grounded at or near where the AC line is grounded at the service entrance. That makes the combined ground path length the distance from the AC outlet to the service entrance plus the distance from the TV box to the cable ground.
post #14 of 16
Thanks Bill for the explanation. I have never thought of in those terms!
post #15 of 16
Quote:
Originally Posted by derrickdj1 View Post

Thanks Bill for the explanation. I have never thought of in those terms!
This explains loops in detail, and why unbalanced connections are the worst enemy:
http://www.rane.com/note134.html
post #16 of 16
Quote:
Originally Posted by Bill Fitzmaurice View Post

Ground loops aren't caused by poor grounds, they're caused by good grounds, just too many of them. The cure is to remove one of the ground paths via transformer isolation.

Words to live by.

Often the most inexpensive ways to remove ground loops are signal transformers. For TV/cable there coax ground isolators and they can work. For audio there are RCA ground isolators and they can work.

http://www.amazon.com/s/?ie=UTF8&keywords=coaxial+ground+loop+isolator&tag=googhydr-20&index=aps&hvadid=7878051589&hvpos=1t1&hvexid=&hvnetw=g&hvrand=13703375121619223128&hvpone=&hvptwo=&hvqmt=b&hvdev=c&ref=pd_sl_68f8p1g194_b

http://www.amazon.com/s/ref=nb_sb_noss_1?url=search-alias%3Daps&field-keywords=rca+ground+loop+isolator&rh=i%3Aaps%2Ck%3Arca+ground+loop+isolator

Often you can just run audio or multichannel over a piece of Toslink fiber and exploit optical outputs and inputs that are already there.

http://www.amazon.com/s/ref=nb_sb_noss_1?url=search-alias%3Daps&field-keywords=toslink&rh=i%3Aaps%2Ck%3Atoslink

I show Amazon sources, but they have no magic. Just google - there are many suppliers.
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