Help with audio hum, and scrolling display lines.

Discussion in 'AV Receivers' started by Vic Matthews, Apr 26, 2005.

  1. Vic Matthews

    Vic Matthews Auditioning

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    I am new to home theater and to this forum, but I'm hoping you can help me out. I just set up my new Panasonic 50" plasma, Pioneer VSX-914k receiver, and got my HD box and cable service. I am getting some type of interference that is showing up as a hum through the subwoofer, and as white horizontal lines scrolling up the display screen.

    Here are some key observations. If I route my component cables directly from the cable box to the display, the problem is much less, but when routed through the Pioneer receiver, it is unbearable. I thought it was a problem with the receiver, so I returned it and bought an Onkyo sr602, set it all up, and had the same problem. Why are the lines so much worse through the receiver? How can I get rid of them? Is there some type of power filter I can buy that will eliminate this?

    Any help would be appreciated. Thanks.
     
  2. John Garcia

    John Garcia Executive Producer

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    What do you have everything plugged into? What else is on that circuit? Sounds like you have noise on that circuit.

    If you disconnect the cable, does the hum go away in the sub? If so, you can use an isolation transformer - about $10 from www.partsexpress.com
     
  3. Vic Matthews

    Vic Matthews Auditioning

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    I have everything plugged into a Monster surge protector. I have not tried disconnecting the cable, but the hum goes away when I route the cable box directly to the display instead of through the receiver. Of course I'd prefer to have everything through the receiver. Thanks.
     
  4. John Garcia

    John Garcia Executive Producer

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    Some similar info on the video issue:

    http://www.hometheaterforum.com/htfo...vertical+lines

    Ground loop hum, which can cause the problem with the sub, is caused by an improperly grounded cable feed. Maybe your provider can come out and fix or check it; it could be something simple.
     
  5. DavidNighorn

    DavidNighorn Stunt Coordinator

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    You appear to have a ground loop caused by different ground potentials between the cable outlet and the electrical outlet where your receiver is plugged in. I had the same problem. My solution was to buy a cable grounding block at Radio Shack ($2) along with some 14 gauge single strand wire. Run the cable from the wall to the grounding block. Then run another cable from the block to your receiver.

    Finally, run the single strand wire from the wiring block to the ground screws in the electrical outlet that the receiver is plugged into. The ground screw can be found by removing the plastic outlet cover. (To be safe, you really should shut off the breaker first.) With the cover removed, you'll see two screws that hold the outlet fixture in place. Simply unscrew one of these a bit, and then wrap the end of the single strand around the screw. Tighten it up and replace the cover.

    You now have a common ground for your cable and your electrical outlet. This fix completely removed any hum from my system.

    David
     
  6. JunoVazquez

    JunoVazquez Stunt Coordinator

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    Hear Ye!

    Call your cable company and tell them to fix the problem.
     
  7. Vic Matthews

    Vic Matthews Auditioning

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    Thank you to everybody who replied, but especially to DavidNighorn who hit the nail right on the head. I have no idea why, but this solution worked perfectly and completely cured both the audio hum and horizontal scrolling lines on my display. I am very happy now.

    Thanks again, you guys are great.
     
  8. John S

    John S Producer

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    You know it is funny. I have been grounding / regrounding this stuff back to the electrical panel.


    This solution, I'll bet is just a effective and a ton simpler.
     
  9. Vic Matthews

    Vic Matthews Auditioning

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    Yeah, actually, I just opened the outlet and tied the cable ground under the screw with the existing ground for the outlet. Seems to have worked great.
     
  10. DavidNighorn

    DavidNighorn Stunt Coordinator

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    Glad to have helped. There is nothing more frustrating than a 60 cycle hum coming from $20,000 worth of equipment.

    David
     

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