LFE humming problem

Discussion in 'Speakers' started by greg_mc, Jun 1, 2004.

  1. greg_mc

    greg_mc Extra

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    I have a problem to solve with my subwoofer configuration. I bought the following items from Parts Express.

    Qty Part Number What
    4 261-400 Coax to RCA wall plate w/091-1200
    1 261-406 Coax to RCA wall plate (4 RCA plugs)

    I am on the final stages of completing a dedicated home theatre. I ran in-wall LFE runs (RG-6) to all four corners of the room and will only use one location at a time. Not sure where will be best location for subwoofer so wanted to build the room to be flexible. I brought all four cables to the rack room. I installed part number 261-400 at the wall to convert coax cable to an RCA plug at all four corners. In the rack room I had all four RG-6 cables terminated to part number 261-406 so I could patch LFE signal to any corner of the room. My thought was to send the LFE signal from the A/V receiver to part number 261-406 in the rack room using monster subwoofer cable. In the home theatre at the corresponding corner, I connected (with monster subwoofer cable) the LFE input on the subwoofer to the wall (part number 261-400) as both ends of cable are RCA. Well, this is where the problem starts, when I plug the powered subwoofer into the wall, the subwoofer starts a humming sound. Unplug the cable from the wall and sound goes away. I then ran the subwoofer cable directly from the receiver to the subwoofer and everything works like it is supposed to. So I am using correct output from receiver and correct input on subwoofer. If I touch one end of subwoofer cable while it is plugged in subwoofer, I get same humming sound. Any advice on how to solve my humming problem?

    Cheers,
    Greg
     
  2. Ivan P

    Ivan P Stunt Coordinator

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    The only what I can think about is ground loop.
    What is the power connector of your subwoofer?
    Mine was with 3 "pins" I bought cheap 3-2pins adaptor to eleminate the ground and that solve my problem.
    It is easy and cheap to test.

    Good Luck
     
  3. greg_mc

    greg_mc Extra

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    Power connector? It plugs into elec outlet on wall for power. Only other connection is the single subwoofer cable. How do you test then? Forgive me but I am confused on your post. Could you please explain.
     
  4. Ivan P

    Ivan P Stunt Coordinator

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    Sorry I didn't explain good.

    Try floating the ground plug at the 110V outlet by using a ground lift adapter (small device you can purchase at any hardware store that plugs onto the end of the power cord to convert the plug from 3 prong to 2 prong). Beyond that, it's probably a bad intetconnect cable or grounding issue with another piece of equipment like your receiver or cable TV

    HTH
    Ivan
     
  5. Leigh_M

    Leigh_M Stunt Coordinator

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    Greg,
    Please post a solution when you find one. I have the same issue in a house purchased that was pre-wired for 5.1.
     
  6. DerekF

    DerekF Stunt Coordinator

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    FWIW, I had the same problem a couple of years ago, evident from the first time I powered up my sub through my new in-wall wired system, [​IMG] though I was lucky that I was able to get to the cable through a crawl-space.

    I replaced the cheap no-name cable with a higher quality 25 ft “sub cable” (direct from receiver to sub, no connections) and the problem went away. I routed the new cable differently as well, taking care to put more distance between it and electrical wiring.
     
  7. John Garcia

    John Garcia Executive Producer

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    Absolutely DO NOT use a cheater plug on equipment that has a grounded plug. This is very dangerous.

    Try disconnecting your CATV cable. If the problem goes away, then Parts Express sells an isolation transformer for $10 - PN# 180-075, for ground loops, which are most commonly caused by CATV systems being improperly grounded.
     
  8. Ivan P

    Ivan P Stunt Coordinator

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    Well that advice was given to me by technical support where I bought my sub (I won't mension the company but is very good one, and very well known on this forum) even that my whole system is very well grounded I had that problem but using the adaptor I was able to fixed it.
     
  9. Rick_Brown

    Rick_Brown Second Unit

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    I had a similar problem - when I unplugged the cable tv line the hum went away. Fixed it by plugging the cable box and the subwoofer into quality power bars.
     
  10. greg_mc

    greg_mc Extra

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    Upon returning home from work today with my 3-prong to 2-prong electrical adapter, I noticed that my subwoofer electrical plug is only 2 prongs (no third grounding plug
    on sub). Oops! Just for grins, I plugged the new adapter into wall and to sub but problem resists. Still hums. I found a drop cord with 3 prongs on both ends. I plugged sub into this drop cord and problem still persists. Any suggestions?


    I have no CATV connected to any equipment yet nor do I have a VCR connected. Only pieces connected are receiver, DVD player, front projector, and CD player. No hum if I run subwoofer cable directly from revceiver to sub.
     
  11. Andy_Steb

    Andy_Steb Stunt Coordinator

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    It doesn't sound like ground loop to me. Your probabley picking up that hum with your homemade sub cables (all those different wires and terminators.
    Does it hum in all four corners? I would try replacing the coax in the walls with RG-6 quad shield.
     
  12. greg_mc

    greg_mc Extra

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    Yes, it hums in all four corners. Not using homemade sub cables. I am using RG-6 quad shield in the walls as recommended by Parts Express. Am using monster sub cable from receiver to start of rg-6 in rack room and then again in all four corners from wall to sub.
     
  13. John Garcia

    John Garcia Executive Producer

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    If no CATV is hooked up, then the wire (in wall) is likely picking up interference - too close to power somewhere, based on what you said, and the isolation transformer probably will not help.

    Ground loop CANNOT be fixed with power bars, nor muffins. [​IMG] I have a Panamax 5100 and I still had ground loop hum in my sub, which goes away when I disconnect the cable. Solution: isolation transformer.
     
  14. Andy_Steb

    Andy_Steb Stunt Coordinator

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    How long is your cable run?
    I just read on another forum that coax is better for hi frequencies. Try using 22ga shielded twisted pair wire(microphone wire).
    I can't say it will work, but it might be worth a try.
     
  15. greg_mc

    greg_mc Extra

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    Problem solved! Humming has gone away. I did have open ground loop. I re-looked at my RG-6 connections at the four corners. Turns out I did not allow enough of the copper conductor in the RG-6 wire to be inserted into
    the coax-RCA adapter. So it was not making contact with the adapter. Plus one of the connectors was damaged (or I damaged it) so will have to get another one. Once I recut the RG-6 and ensured a longer copper piece was present, the humming went away. Three of four corners are now hooked up and ready to rock with the LFE signal. Thanks for your input on my problem.
     
  16. Andy_Steb

    Andy_Steb Stunt Coordinator

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    Glad you got it fixed.
    I'm sorry all my suggestions led you in the wrong direction. I figured it was the RG-6 but never figured a bad connection, because it was doing it in all four corners.
     

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