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Ground Loop Problem?

Discussion in 'AV Receivers' started by Robert_Lamb, Dec 20, 2003.

  1. Robert_Lamb

    Robert_Lamb Stunt Coordinator

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    I connected my S-Video cable between my Sony Wega TV and my Anthem AVM 20 and I hear a buzzing sound through my speakers. These two devices are plugged into different electrical outlets but they are on the same circuit. Any thoughts in how to eliminate the buzz?
     
  2. Michael Mohrmann

    Michael Mohrmann Screenwriter

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    Robert,

    It could be a ground loop problem, and the first area I would look at is your TV reception, presumably cable TV or satellite dish. Both of these TV systems are notorious for causing ground loops.

    Disconnect the coax TV line at the wall, so that no device (TV, VCR, cable or sat box, PVR, etc.) is connected to the outside TV system. If the buzzing goes away, you have found your culprit.

    Michael
     
  3. Bret Pritchett

    Bret Pritchett Stunt Coordinator

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    I had the same problem when I got a my X1 projector.

    I got a ground loop isolator off ebay
    check here
     
  4. Robert_Lamb

    Robert_Lamb Stunt Coordinator

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    I have totally taken apart my system and reassembled it piece by piece. Am amplifier is connected to the AVM-20.

    My satellite hookup is a little complicated. I have a multiswitch that is grounded. I have grounded the multiswitch to my electrical ground (with no success in hum reduction). The satellite is connected to the multiswitch, splitters, amplifier, etc. I have two receivers that return to a signal combiner with a roof antenna as well. This produces a combination signal that is distributed throughout the house.

    After all of my trouble , I've come to the following conclusions:

    1. Playing a recorded program from the TIVO does not cause the hum. No other connections to the TIVO at this time. Therefore it is not the TIVO.
    2. Connecting pieces such as the DVD or CD player (which were connected to the TV) did not cause the problem.
    3. Connecting any coax cable in my satellite system causes the hum (either from the satellite in connection, satellite out connection or the combination of all signals connection that connects to the TV).
    4. Grounding the multiswitch to the electrical ground did not help.
    5. I did some reading and tried a 75 ohm to 300 ohm transformer and connected it to a 300 ohm to 75 ohm transformer. Basically I made a coax isolation transformer. I installed this in various places and each time it made the hum go away. The problem with this approach is that I would need to install at least 3 and possibly 6 of these transformers to resolve the issue (1 for each connection - satellite in, out and combination signal). Each causes some degradation to the signal and this is not an optimal approach.
    6. This problem does not appear to be an electrical ground issue between components but rather a problem with the ground from the satellite system to other components.

    Does anyone have any ideas on how to trouble shoot this further or eliminate the problem?
     
  5. Riche_guy

    Riche_guy Auditioning

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    Check to see if it is an rca cable or your coax cable that is causing the hum, unplugging cables until the hum stops. Once you have localised the humming try taking a wire an wrapping it around the metal part of the connection and grounding it. Check to see if in back of your receiver you have a ground connection. Connect the wire there. This should get rid of your humming. If it doesn't, check to see if the cable head wires has become unsoldered. If so resolder or replace.[​IMG]

    Riche_guy
     
  6. Robert_Lamb

    Robert_Lamb Stunt Coordinator

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    I grounded all of my coax cables together and to the electrical ground. I tied the electrical ground and the satellite ground together. I also put in the filters between the TIVO and TV and the TIVO RF out back to the multiswitch. This reduced the hum by about 80%.

    Unfortunately, 20% hum is still a lot of hum. I believe that this issue happens via the coax cables.

    I did try to ground the processor ground to this common ground as well. It didn't make any difference.

    Any further ideas to help eliminate the last 20% of the hum?
     
  7. DavidLW

    DavidLW Stunt Coordinator

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    Try placing cheater plugs on all your three prong plugs except one of them. All your equipment are grouned to each other by way of RCA or Coaxial cables. It's not a matter of having a piece of equipment not grounded by rather having two or more ground sources. This may cause hums if the ground sources have different potentials. Even if the outlets are on the same circuit. By only having one piece of equipment grounded at the outlet you eliminate the multi-ground source.
     
  8. Michael Mohrmann

    Michael Mohrmann Screenwriter

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    David,

    When I was investigating our ground loop problem (cable TV) a couple of years ago, I was told that a single ground source was required to eliminate the problem. So, when a cable TV or satellite dish installer grounds their system using a separate grounding rod, are they in fact creating the ground loop problem? I think this is what you are saying, but if not, please elaborate further. Thanks! [​IMG]

    Michael
     
  9. JasenJ

    JasenJ Agent

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    I just dealt with this same problem this weekend. The 75->300->75 transformer worked well enough for me (and only $6.00 in parts[​IMG]). If that solves your hum problem but the quality degrades too much, there are fancier transformers available. Try a little Googling for "cable tv isolation transformer". (I tried posting some links but I haven't posted enough to have permission for that.)

    - Jasen.
     
  10. Robert_Lamb

    Robert_Lamb Stunt Coordinator

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    I believe the single ground is the correct solution to the problem. I have tied the multiswitch ground to the electrical system ground. I have also plugged all equipment into 1 outlet via a power strip. I further grounded the ends of the coax cable that connect to my home theater equipment from the satellite system to the electrical system ground. I left in my 2 transformers for now as well to isolate the TIVO and TV. All of this together has reduced the hum to only be heard in the center channel when you place your ear right next to the speaker.

    It wasn't a fun experience, but I think I understand this problem a lot better now. I guess I need an electrician to properly ground the satellite system with the electrical system.

    I think the same thing can be accomplished by using a product like Monster's HTS 2000 or Paramax's MAX 8 DBS+5. These two devices tie the grounds together for both the electrical components of a home theater as well as the coax and phone line needed for satellite / TIVO. This in theory should also provide a common ground and may help resolve the problem for others as well. I am going to try this as it is probably better in the long run to have a surge protector and common ground close to the equipment.

    I'm not a proponent of the cheater plug idea. It sounds like you could route potentially harmful voltage / current through other components of your system (and potentially yourself in a ground fault).

    Thanks for the ideas. It really took a lot of information from various forums such as this to help me troubleshoot the issue.
     
  11. Kevin. W

    Kevin. W Screenwriter

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    Robert if your Anthem has a screw type FM antenna hookup run a TV coax cable from it to the CATV IN on a surge protector and see if it grounds it for you. I have this problem in my setup and by doing this the hum/buzz is gone.

    Kevin
     
  12. Steve Bruzonsky

    Steve Bruzonsky Auditioning

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  13. MikeTz

    MikeTz Stunt Coordinator

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    Robert:

    I believe you are right. The cause of your ground loop is probably because your satellite/TV antenna system including multiswitch, grounding blocks, etc. are not bonded to the electrical service ground of your home. Grounding rods are great if they are bonded to the home service entrance. Using a cold water pipe is also no assurance of a proper ground.

    Make sure all your satellite and antenna systems are connected via single point to your home electrical service ground. Lack of a single point ground is usually where CATV/satellite ground loops are created.

    MT
     
  14. Brian Treinen

    Brian Treinen Stunt Coordinator

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    I had a similar problem and for about a year suffered through the 75>300
     
  15. Robert_Lamb

    Robert_Lamb Stunt Coordinator

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    There is actually more devices to buy for cable TV; however, satellites are slightly more complicated. You can not put an isolation transformer between the receiver and the multiswitch. If you do, you no longer get reception.

    The best results for me is a single ground point in my house. I found that the satellite ground was not installed properly and did not meet the National Electric Code. I will have this fixed as well as I purchased a Paramax MAX 8 DBS+5 surge protector. This will provide a single ground point for all of my gear and connections. This should additionally make the problem go away. It was about $70. It was the only product that I found that met my needs for grounding in this price range. It can take care of power connections, satellite and phone connections.

    Thanks for the ideas.
     

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