Subwoofer is humming

Discussion in 'Speakers & Subwoofers' started by JoshGivens, Sep 8, 2004.

  1. JoshGivens

    JoshGivens Stunt Coordinator

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    I have an Acoustic Research prepowered subwoofer that hums. It doesn't hum when the RCA cables are unplugged from the back of the Sub. The setup consists of a high quality Y coming out of the pre amp output of the receiver to a high quality 10' RCA cable that connects to the L and R inputs on the sub. Also, when I plug up only the left or only the right, the humming will start, but if I touch the pole of the other cable to the outside metal jacket of one of the other connections on the back of the sub, the humming will stop.

    Could the cable be bad? Am I hooking this up incorrectly or are you supposed to split the signal from the back of the receiver?

    BTW, I just got a new receiver and the problem existed on my old receiver as well.
     
  2. John Garcia

    John Garcia Executive Producer

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    Disconnect your cable (CATV) from the system. If the humming goes away, you have a ground loop issue, which may or may not be easy to solve. I was able to solve my issue for $9.

    It doesn't matter if you split the signal at the receiver or at the sub, this should not cause the problem you are describing.
     
  3. JoshGivens

    JoshGivens Stunt Coordinator

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    What did you do to solve the issue in case this is the culprit?
     
  4. Dave Man

    Dave Man Stunt Coordinator

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    I agree that a ground loop problem could be the problem. I'm not too familiar with the technical side of this issue, but here goes my best effort. Chu or someone is more than welcome to chime in here.

    I believe that a ground loop occurs when you have components plugged in to different AC circuits. In your situation, and mine before I made a change, it was a subwoofer. The equipment wants to ground itself in the shortest distance possible, so it may travel down the RCA cord to the amp or receiver and ground out there rather than the circuit it is plugged in to. That is why the hum goes away when the RCA line is unplugged (plus there is no audio signal...lol) Try running both your sub and receiver or amp, etc from the same outlet with an extension cord (temporarily). If this eliminates the problem, you could probably get away with a heavy duty extension cord for a permanent fix.

    I may be way off in that explanation. If someone can explain group loop better than that, please post here so I can understand it better.

    David
     
  5. JoshGivens

    JoshGivens Stunt Coordinator

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    I'll try that when I get home but until I moved the sub recently, I believe that the receiver and sub were plugged into the same outlet. I'll give it a try as well as unplugging the cable.

    Anymore suggestions would be greatly appreciated. I'm willing to try anything so I don't have to purchase another sub right now.
     
  6. Dave Man

    Dave Man Stunt Coordinator

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    Josh-lots of very knowledgeable people on the klipsch website too. Use the "technical questions" section.

    www.klipsch.com

    David
     
  7. JoshGivens

    JoshGivens Stunt Coordinator

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    Well, when I got home, I disconnected the CATV line and the humming was stopped. So now is there something I can do to correct this problem or do I need to call the cable company and have them come check it out?
     
  8. John Garcia

    John Garcia Executive Producer

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    This is very common with CATV systems - bad grounding of the cable where it comes into the house. I told my cable company that I had this problem and they never bothered to do anything about it.

    I used the www.partsexpress.com isolation transformer PN# 180-075. Worked like a charm. Radioshack used to sell something similiar as well, but I couldn't find it on there any longer.
     
  9. JoshGivens

    JoshGivens Stunt Coordinator

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    Well, I checked around on some other sites and they suggested using a "cheater plug." In other words, an adapter that converts from a 3 prong plug to a 2 prong plug. This fixed my problem.
     
  10. John Garcia

    John Garcia Executive Producer

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    I strongly recommend against using a cheater plug, which is why I did not mention it. You are removing the ground on an item that is designed to have one.
     
  11. brentl

    brentl Cinematographer

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    "I have an Acoustic Research prepowered subwoofer that hums"

    do you recognize the song?


    [​IMG]

    Brent
     
  12. JoshGivens

    JoshGivens Stunt Coordinator

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    The cheater plug is just a temporary fix until I can get an Isolation Transformer that was referred to earlier.

    How exactly does the transformer work? How is it hooked up?
     
  13. John Garcia

    John Garcia Executive Producer

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    The transformer just installs somewhere in the cable line. I put mine between the cable and the jack at the wall socket. As far as how it works, I'm not 100% sure, but I believe it works along the lines of a cheater plug, but since it is a low voltage signal line, it is not as potentially dangerous as removing ground from a 120vac component.
     
  14. Dave Man

    Dave Man Stunt Coordinator

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    BrentL-"All your base are belong to Silica." Do you play SOCOM?

    David
     
  15. Brian L

    Brian L Cinematographer

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    I am sure a EE will chime in to correct me, but a transformer as discussed here will decouple the ground from the cable system to your rig.

    It does this by passing the signal electro-magnetically (the signal passes from one set of xformer windings to the other), but there is no actual cable connection. It functions as an isolation transformer that passes the signal in a 1:1 fashion (no step up or step down).

    FWIW, recent S&V Q&A advised using one, but the next month, a cable TV engineer wrote in to say that it was NEVER a good idea to do this. Of course, they will not come to your house to help fix the problem either!

    BGL
     
  16. JoshGivens

    JoshGivens Stunt Coordinator

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    Did they give reason as to why it wasn't a good idea to do this?
     
  17. Brian L

    Brian L Cinematographer

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    Yes.

    But I'll be damned if I can recall what it was!

    I keep my old issues...if I get a chance, I will see if I can find out. It is also possible that it may be available on line at the S&V site.

    BGL
     
  18. brentl

    brentl Cinematographer

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    "All your base are belong to Silica" why yes, yes they do[​IMG]

    but no I don't!

    B
     
  19. Brian L

    Brian L Cinematographer

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    OK, I looked through my magazine pile, and could not find the article I referenced. So, that means I either made it all up, it was in a S&V that has been tossed, or it was in a different magazine.

    I will keep looking, but if anyone elses recalls any mention of this subject in S&V, please chime in and save my sorry ass.

    BGL
     

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