DIY sub cables & ground hum

Discussion in 'Accessories, Cables, and Remotes' started by Antony, Jan 27, 2004.

  1. Antony

    Antony Agent

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    Hi all,

    Here's the history: built a beautiful end-table enclosure to Adire ported specs for a Dayton DVC 12, and am using the PE250 plate amp. Everything sounded great! (Was using a 16 foot Monster sub cable).

    Then everything went into storage while we moved into our new house. The builders of the house installed a dedicated 20A circuit for the HT, and "pre-wired" for 7.1 surround exactly where I told them to. I seem to recall them telling me that I'd get a coax for the sub (but can't recall exactly).

    I dug into the wires last night in an attempt to fire up my sub. Found out that they ran only one 16 ga 4-conductor speaker wire, and one 18 ga. 4-conductor speaker wire to the sub location! I was a bit disappointed, but wanted my sub working for the evening's movie. I soldered on a couple of nice Phoenix Gold RCA ends (left over from the car stereo days) onto 2 of the 4 larger ga. speaker wires, and plugged them into the respective ends.

    As soon as I plugged the amp into the wall socket, it began humming like crazy. I had to turn down the gain to watch TV. Unfortunately, my receiver can't compensate enough for the lowered gain (almost to 0).

    There is no physical way to plug the sub and the receiver into the same outlet/circuit. There is no physical way (aside from breaking drywall to fish a true sub line-level cable into the wall - wife won't like that solution).

    I have not tried the 'cheater plug' idea yet. Can I use the other 2 wires of the speaker wire to either create an electro-shielding by grounding them or running a current through them? Or will it help if I doubled up on the wires soldered to the RCA ends? Or am I doomed to using a 'cheater plug', assuming that helps?

    Any suggestions are appreciated!!

    Thanks,
    Antony
     
  2. David-S

    David-S Second Unit

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    Did you try unplugging your cable tv?
    That is where my hum comes from, you can use one of the "dual transformer" methods, or, if it's a new house, complain to the cable company that the ground is bad...
     
  3. Antony

    Antony Agent

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    David-S, I thought of that, but I don't have cable. We're exclusively Dish Network, and I believe that the dish is grounded at the point of entry to the attic (I'll have to double check that one!).

    Antony
     
  4. Stephen Hopkins

    Stephen Hopkins HW Reviewer
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    you could run your mains as large and use the 16ga 4 conductor line to send a high-level signal to the PE amp. Then use the amp's crossover instead of the receivers and set the sub to off on the receiver. It's not an optimal setup, but will get rid of the hum and make the sub easier to blend with your mains.

    Hope this helps [​IMG]
     
  5. Patrick Sun

    Patrick Sun Moderator
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    As long as the PE amp is hooked up to an electrical outlet, the hum will probably be there, so hooking up the speakers to it to the PE amp and using it for the crossover won't make much difference.

    Try the cheater plug.
     
  6. Stephen Hopkins

    Stephen Hopkins HW Reviewer
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    I don't think his hum is coming from the outlet but instead from using un-sheilded non-coax low-level RCA cable. When I was testing a new sub placement i spliced together a temp cable using some solder RCAs and speaker cable and I had the same problem. When I decided where I wanted the sub and bought a decent sheilded coax based cable the hum went away. The 16ga cable he's using with RCAs soldered to them are probably run parallell to either the cables for his back channels, powere lines, or both. Even if they're not, long un-sheilded non-coax low-level cables are like magnets for interference/hum. Using the cables as high-level in the arrangement i described earlier should eliminate the hum because there's enough current being carried that they won't be affected by EM interference. It should be pretty simple to try out as well.
     
  7. Paul His

    Paul His Agent

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    If your speaker wires that the builder put in for your sub don't run too far around too many corners inside the walls, you could attach a coax cable to one end of the speaker wire and pull it through inside the walls using the speaker wires as a pull string.

    Paul H
     
  8. Antony

    Antony Agent

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    Well, stopped by HD last night on the way home and picked up a cheater plug. The humming was reduced tremendously. I actually thought that it had eliminated it entirely, but then realized that there was still a hum when I shut down the system (sub is on constant on due to the amps inability to pick up a signal for auto-on).

    I think that I can now lower the gain a bit and get rid of it, while turning up the sub level on my receiver (it was too late last night to play around with it).

    Paul - that was my original thought, but they ran the speaker lines up and around a fireplace and around 2 corners. I'll have to review the video tape that I have of the pre-drywall days to make sure.

    I'm actually starting to think that they were supposed to run a coax, and since they didn't it might be a warranty issue. Going to review the documents tonight!

    Thanks to everyone for their suggestions. The cheater plug with lowered gain may be the easiest way out of this mess.

    Antony
     
  9. Antony

    Antony Agent

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    OK, thought I'd update the list on this saga. Turns out that lowering the gain does very little to remove the hum. I also used my old Monster sub RCA cable to see if the hum was indeed caused by the wiring, and upon hook up, it was gone! Using the good sub wire eliminated the hum completely, even without using the cheater plug.

    So I did a bit of research into the paperwork of our house, and found the HT wiring section where they list each wire provided. For the sub, they specifically state that I get 1 16ga. 4-conductor speaker wire, and 1 RG6-QS for line level!! I immediately placed a call to the customer service/warranty guy, and am now waiting for his return call.

    Granted I could probably easily use one of the wires as a pull string to run my own coax, but that would require that I cut and patch approx. 3-5 holes in various places. I'd rather have them do it for free while I'm at work!

    Thanks again for all of your suggestions.

    Antony
     

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