I'm out of ideas - ground loop buzz....

Discussion in 'Home Theater Projects' started by Gary Thomas, Sep 22, 2003.

  1. Gary Thomas

    Gary Thomas Second Unit

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    I've been battling an annoying ground loop problem caused by my satellite connection. Here's the background:

    Dish satellite properly grounded, along with phone ground and house ground at 1 point on grounding rod.

    RG6 cable from outside box to satellite receiver. When I disconnect the cable, the buzz goes away. When connected to satellite reciever, buzz is present even w/ unit turned off.

    I have tried disconnecting every other plug, one at a time, with no effect on the buzz.

    1/2 components plugged into a Panamax surge protector, other 1/2 into a Belkin surge protector. Both plugged into dedicated 20 amp outlet. I tried plugging the Belkin into the Panamax w/ just 1 plug going to the outlet...no effect on the buzz.

    When satellite cable is run through the Belkin surge protector, 50% of buzz goes away.

    I tried a Jenson ISO Max, but discovered it is not compatible with satellite.

    No other grounds in house...with the exception of a plumbing ground - basically it is a 2' long ground wire connecting a pipe on either side of a valve.

    I do have a Lutron dimmer in home theater room, but it is not on the HT outlet. It controls track and rope lighting on the ceiling & in a tray. The track lighting hums a bit when on, but is silent when off.

    What am I missing??? Are there any ground loop eliminators for satellite? Any other ideas?

    Thanks!

    Equipment List:
    Echostar Satellite Receiver
    Panasonic DVD Player
    Denon Receiver
    Samson Amp
    Behringer EQ
    VCR
    IR Repeater
     
  2. John Robert

    John Robert Stunt Coordinator

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    Gary:

    I just went thru the exact same problem with my satellite cable; when I unhooked it hum went away. I solved problem by purchasing inexpensive quad shielded cables and running the connection thru my Monster Power 2600. Does your Panamax have cable in/out???

    P.S. What a relief to get rid of that hum! I was hearing it in my sleep...
     
  3. Gary Thomas

    Gary Thomas Second Unit

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    John:

    Yep, I am running it through the Panamax...which reduces the buzz. Also, it seems as though the Panamax eliminated the buzz from the main speakers, but left it in the subwoofer.

    Interesting suggestion about the cheap cable...I actually tried a better quality cable & the buzz got louder!
     
  4. Matt_Doug

    Matt_Doug Stunt Coordinator

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    Run your satellite cable through the belkin surge protector and plug your sampson amp and any other component with a 3 prong plug into it also. If you still get significant hum its your dimmer or a component with a noisy rf modulator like your satellite box, tv...etc
     
  5. brucek

    brucek Second Unit

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  6. Gary Thomas

    Gary Thomas Second Unit

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    There are 4 cables going about 10 feet from the dish to the grounding block. 1 of the cables has an attached ground wire that goes from the arm of the satellite dish to the grounding block. The grounding block has a ground wire that goes about 8 feet to the house grounding rod. Also attached at the rod is the house ground and the phone ground. The 4 cables go from the grounding blocks to 4 locations inside the house. The run to the HT in question is pretty long...about 50 feet.

    The receiver has the following cables attached:

    S-Video + Audio From VCR
    Toslink + S-Video From Dish
    Toslink + S-Video From DVD
    6 Audio Cables from DVD for DVD-A
    S-Video Out to TV
    Sub Line Out to EQ, then to Amp.
    Plug "in" from Panamax Surge Protector

    Thanks!
     
  7. Parker Clack

    Parker Clack Schizophrenic Man
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    Gary:

    If you unplug the satellite feed does the hum go away, in particular to the sub?

    Parker
     
  8. Gary Thomas

    Gary Thomas Second Unit

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    When I unplug the satellite feed, the hum goes away in all speakers, including the sub. It is dead silent!
     
  9. brucek

    brucek Second Unit

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  10. Gary Thomas

    Gary Thomas Second Unit

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    I may have hit on something...

    I previously unplugged every other component one at a time w/ no improvement. I didn't think to unplug both the subwoofer amplifier and the subwoofer EQ. That did the trick. The hum stays gone when I lift the ground (using a 3-2 plug adapter) on the plugs of the amp & eq.

    Since I don't want to lift the ground permanently...what can I do to fix it safely?

    Bruce:

    The hum disappears when I disconnect the feed to the satellite receiver. If I don't go through the surge protector the hum is much worse.

    It seems as though the hum is a result of problems between the satellite ground and the subwoofer amp & eq ground.
     
  11. brucek

    brucek Second Unit

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  12. Gary Thomas

    Gary Thomas Second Unit

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    Fantastic Post Bruce!! It will take me a little while to digest it...

    The ground wire from the satellite block to the house ground is, I believe, 8 gauge. The 8 barely fit into the hole in the grounding block...I'm not sure if a 6 would fit!

    The ground from the dish to the block, however, is very thin...probably 21 gauge. Should I replace that with the 8?

    The EQ is a BFD. The equipment rack is located under stairs in an unfinished part of my basement. I use IR repeaters to control the system. The BFD is on the bottom shelf...no one should really go near it for any good reason. Cheating the BFD would do what kind of damage...shock, destroy the component... and what would cause such a problem?

    I will definately check the cables from the satellite block to the satellite receiver...I used a connector to go from the original location to my equipment rack. I may replace the original cable (from the block to the basement) just for the heck of it...I've got some good quality RG6 laying around.

    Thanks again!
     
  13. brucek

    brucek Second Unit

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  14. Parker Clack

    Parker Clack Schizophrenic Man
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    Gary:

    You can also try putting a group loop isolator in the line between your satellite feed and your receiver. One such device, that a lot of members have used, is the Mondial Magic Box. It is a bit pricey but I have heard that it actually improves the picture quality too.

    Parker
     
  15. brucek

    brucek Second Unit

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    Since a satellite horns block amplifier receives its DC power from the receiver through the RG-6, you are not allowed to break the shield with one of these transformers....
     
  16. Matt_Doug

    Matt_Doug Stunt Coordinator

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    Gary tried a line level isolator (jensen catv isomax ) anyway and he found it incompatible with his satellite receiver. I belive for 2 reasons: as Bruce mentioned passive rf amp/splitters draw their DC over the shields of coax connections from the receiver. Lift the ground, block the dc, no amplification of the sat signal. Also there is an insertion loss with the catv isolator which worsens the attenuation of the unboosted sat signal. This doesn't happen in cable cause their signal is boosted. But wouldn't adding an active rf amp allow the catv isolator to be used? more money I know. Also, why wouldn’t grounding everything with an earth ground reference at one point (the belikin surge protector) work also? As long as all safety grounds are established, secondary at site equalization of ground potentials shouldn't be a safety issue. Bruce laid out so many possible reasons for the potential difference you may never find it.
     
  17. brucek

    brucek Second Unit

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