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Ground Loop Problem?

Discussion in 'AV Receivers' started by David Berry, Aug 6, 2002.

  1. David Berry

    David Berry Stunt Coordinator

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    Ok, I will try to keep this short and to the point.
    I recently bought a Bryston 3B-ST amp and hooked it up via the preouts on my Denon 3802. As expected, the mains started to hum. Alright, I smugly thought, I've read the posts here, it is probably a ground loop potential problem between the cable and house ground. I disconnected the cable and, voila, the hum disappeared.
    As I do not believe in cheater plugs, I decided to tie the two grounds together to relieve the ground loop. We have one cable coming into the house and I have it connected to a 1 into 4 booster box I bought at the Home Depot. One goes to our TV upstairs, another to the VCR upstairs, another to the TV downstairs, and the final one into the back of the Denon for FM reception - all short (less than 10 foot runs).
    There is a ground block on the RG-6 cable coming into the house in which the ground wire was attached to our hydro meter. I disconnected that and ran the wire directly to one of the ground screws in our beaker box.
    As you guys can guess, I am writing this because when I turned everything back on, that hum was still there[​IMG]
    What gives!
    Also, I checked to see if the outlet was grounded. It is.
    Any suggestions are appreciated. I do currently have the 75-300-300-75 ohm transformers hooked up as suggested on this forum. That does get rid of the hum, but I want to solve this riddle.
     
  2. mike_decock

    mike_decock Supporting Actor

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    From what I've gathered, the only way to solve a cable ground loop problem permanently is to call the cable company and have them fix it.

    Sorry...

    -Mike...
     
  3. Lee-c

    Lee-c Second Unit

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    Since the cause of these annoying hums is usually the cable t.v., I just thought I'd provide
    a link to a product that is supposed to solve the problem. A fellow forum member mentioned
    this RF Isolator from Jensen will eliminate the hum, and works as just as well as the Magic Box
    from Mondial, but only costs about half as much.
    I've got one on order.
    So, for around $50 you can solve the problem in total safety and supposedly it can even improve
    your cable t.v. picture quality (apparently those ground loops cause more than just hum in
    your equipment).
    Check out the link below to get one.
    http://www.jensentransformers.com/vr1ff.html
     
  4. Wayne A. Pflughaupt

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    Wayne
     
  5. Selden Ball

    Selden Ball Second Unit

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    Wayne,

    Many cable systems carry FM radio stations. Our local Time Warner affiliate certainly does.

    David,

    The grounding of the incoming CATV cable is a safety issue more than it is a signal quality issue. There are federal and state regulations about how it has to be done. You really should have the cable company "do it right," which may include installing a grounding stake deep into the dirt where the cable enters the building.

    Of course, this may do nothing to help get rid of the hum. A ground isolator where the coax connects to the first amp is probably your best bet. You should also take a look at where the amplifiers get their power. They may be contributing to the problem. It'd be best if they were plugged into a power strip that's plugged into the same outlet with the rest of your A/V gear.
     
  6. mike_decock

    mike_decock Supporting Actor

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  7. Wayne A. Pflughaupt

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    Wow, interesting story, Mike!
     
  8. David Berry

    David Berry Stunt Coordinator

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    Thank you guys for the input.
    The FM reception via the cable is great! I receive over 40 FM stations crystal clear. As to the implementation of another grounding stake for the cable, it is my understanding that that would, almost by definition, possibly cause a ground loop because the ground potential could be different from the electrical ground. I will phone the cable company and let them have a look at it.
    The amplifier is on the same 15 amp circuit as the rest of the AV system and there are no dimmer switches on that line.

    Lee,

    Thanks for the link.

    David
     
  9. Selden Ball

    Selden Ball Second Unit

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    David,

    Good luck with the grounding!

    Wayne,

    Lots of people do seem to like upstate NY: hills and waterfalls and gorges... and *very* changable weather.
     
  10. Lee-c

    Lee-c Second Unit

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    UPDATE: I just got the cable t.v. isolator from Jensen. I installed it and the hum
    is history! [​IMG] It sounds the same as if I disconnected the cable t.v. entirely from
    my system, that's how thoroughly it works! No cable t.v. induced hum, period.
    I highly recommend this as a relatively low cost way to get rid of the cable t.v. hum
    once and for all. I can personally verify that it works. And no need for cheater plugs
    or anything else.
    The link to this product is in my post above.
    I recommend you also get the 6 inch top-quality cable that Jensen offers made by Canare
    for them, if you need a small a section of cable to bridge the gap made by adding the isolator
    to the system.
     
  11. Lee-c

    Lee-c Second Unit

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    2nd UPDATE:

    Jensen is coming out with a new model of their cable t.v. isolator that will cover
    a broader frequency range.

    They say this should eliminate any chance of introducing visual artifacts into cable t.v.
    channels (about 1 in 20 peoples' cable t.v. will see a few channels where the image
    suffers when connecting the current model isolator, the newer model shouldn't have this
    problem at all) when using their isolator. This newer model should be available in about a month.

    So, if you are considering getting one of the Jensen Iso-Max devices (link provided in post above)
    to get rid of cable hum, you might want to wait another month and get the improved model.
    I assume price will be the same, but I'm not sure.
     
  12. Scott Sabin

    Scott Sabin Stunt Coordinator

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    David,
    Although your incoming cable coax is grounded to your water pipe (and you also tested by connecting to a ground screw in your main panel), the ground potential is probably sufficient enough that the relatively small ground wire you have doesn't do an adequate job of grounding the coax. Try significantly reducing the ground wire length, or even better, run two or three ground wires in parallel to reduce the resistance.

    My guess is that your ground wire is 14 gage, and in reality, you might need an 8 or 6 gage wire to squash the ground down to your house ground.

    The best advice, however is to prove the noise is in the incoming cable, then make the cable company fix it. The reason I bothered with this reply was in case you find you are essentially powerless in making the cable company do anything.
     
  13. Drew_N

    Drew_N Extra

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    I had the situation that Scott just described. I asked my cable company to fix my problem and they said no, its not possible. Even though the last cable guy said "Oh god thats bad" the last time he was here, they just don't want to fix it (Comcast).
    My ground loop problem was a visual one with rolling lines, which was unwatchable. I purchased the Dayton Ground Loop Isolator from Parts Express (Part # 180-175 ) and it fixed everything for me. I highly recommend it as a fix when the cable company won't fix your problem. Its a mere $12.
    Link to Dayton Ground Loop Isolator @ Parts Express
     
  14. Brian Burgoyne

    Brian Burgoyne Second Unit

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    Do you need to just use that Dayton isolator on the cable to the TV in your av system or all cables in the house?
     
  15. David Berry

    David Berry Stunt Coordinator

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    Scott,

    Sorry for the long delay in responding, I was just on a one week vacation. For completeness sake, I actually have a 10 gauge wire running approximately 15-20 feet from the cable TV ground block to a grounding screw in the breaker panel. I used 10 gauge wire only because I had it readily available.

    David
     
  16. Mark Austin

    Mark Austin Supporting Actor

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    I had the same problem. Went to the cable company and they re-grounded the cable to the breaker box to no avail. Researched several $50+ options, then came across something from a local A/V store. A simple cable ground breaker. $8.00. Works like a charm.
     
  17. John Chevalier

    John Chevalier Stunt Coordinator

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    i dont really have any audio problems with my system, but i do have horrible picture on some channels. Can I use that ground loop isolater to make those channels better? How can i tell if i have a ground loop?
     
  18. Lee-c

    Lee-c Second Unit

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    If you can hear a significant hum coming from your stereo speakers and your stereo gear
    is hooked in any way to your cable t.v. cable (either through the t.v. or VCR, generally),
    then there is a good chance you have the ground loop caused by the cable t.v. These ground
    loops can also degrade your cable t.v. picture. The device I mentioned above is also supposed
    to get rid of picture problems caused by the ground loop.

    The newer model should be out in less than a month.
     
  19. Lee-c

    Lee-c Second Unit

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    If anyone is having a problem with hum caused by their cable t.v. connection, Jensen has
    their newer model of RF isolator out now. It's called the Model VRD-1FF. I've tried these
    and can confirm they completely eliminate hum in your speakers caused by the cable t.v. connection. [​IMG]
    Link is below if you want to check it out.
    http://www.jensentransformers.com/iso_vid.html
     

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