Sub receiving feedback - what gives?

Discussion in 'Speakers' started by Cliff L, Jun 9, 2004.

  1. Cliff L

    Cliff L Extra

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    Hey all - was hoping y'all would have some advice for a friend of mine. He recently had satellite TV installed and when he hooked it up to his HT system, he said his subwoofer started humming big time. It was like it was getting feedback from the satellite signal and he wasn't sure what was going on.

    We think the culprit is that he has a switchbox at his TV to select between the satellite signal and VCR signal. He has a VERY old TV that *only* has a co-axial input (no RCA composite). So he installed a co-axial switchbox that allows him to choose between the satellite (antenna) signal and the VCR signal.

    Here's how everything is hooked up:

    video:
    DVD ---RCA---> VCR ---co-axial---> co-ax switch ---> TV

    audio/video:
    satellite box ---co-axial---> co-ax switch ---TV

    audio:
    DVD---digital co-ax--->receiver
    VCR---RCA--->receiver
    receiver--->5.1 surround speakers/sub

    Granted the easy solution is to buy a new TV that accepts S-video/composite hookups, but he's still looking and not ready to buy yet. However, for the time being, can someone tell him why the sub is receiving feedback? Is there anything he can do to get rid of it? Thanks for any advice y'all may have.

    Components:
    Denon 1603 H/T receiver
    Ascend Acoustics CBM-170s fronts/rears
    Ascend Acoustics 340c center
    HSU VTF-3 subwoofer
    unknown brand of DVD player, VCR, TV
     
  2. John Garcia

    John Garcia Executive Producer

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    TV input is called RF.

    This sounds like ground loop hum, VERY common with CA/SAT TV systems being improperly grounded. A new TV probably won't solve the problem. If the problem goes away when you disconnect the cable, then this is the problem, and it can be fixed for about $12.
     
  3. Wayne A. Pflughaupt

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    Like John mentioned, it’s probably a ground loop. A ground loop happens when you have two separate paths to earth. What probably happened is that the installer grounded the dish and/or the signal feed “quick and dirty” to the closest ground location he could find – a water pipe, etc.. The ground should go all the way back to the ground stake at the electrical (breaker) panel.

    Regards,
    Wayne A. Pflughaupt
     
  4. RandyMathis

    RandyMathis Stunt Coordinator

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    If he has conduit in his home he could ground the dish to the conduit which works in my house.
     
  5. Cliff L

    Cliff L Extra

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    Is this something he should require the satellite guys to fix? Or is this something he could fix himself? He wrote HSU Research and they said something to the effect of getting an adapter to negate the ground in the subwoofer power cord (i.e. a three-prong to 2-prong adapter). Would that do the trick?
     
  6. Gau

    Gau Stunt Coordinator

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    bad idea! never negate the ground connection with a 3-prong to 2-prong converter. the ground connection is there for a reason, dont mess with it.
    i've seen some mention of a ground loop interference filter on these boards somewhere, try that.
    plus, as people said, does the problem go away when you unplug the rf cable?
     
  7. Cliff L

    Cliff L Extra

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    Hey guys - thanks for all the advice. It turns out that the outlet that the satellite receiver was plugged into was grounded improperly. When the satellite guy moved it to a different outlet, the humming went away.
     

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