For ground loop experts only: help!

Discussion in 'Archived Threads 2001-2004' started by Barton Lynch, Mar 19, 2003.

  1. Barton Lynch

    Barton Lynch Stunt Coordinator

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    I have a JBL Subwoofer (PSW-1000) connected to my Yamaha receiver using a high-end MIT Terminator series 5 (10-ft RCA) cable. The problem is that when you touch the cable at the receiver's end, the sub hums, and stops the moment you let go. The receiver is on a surge protector along with the rest of the components, the sub is connected to the wall.

    Let me flash back to this problem's past. The problem was so severe that if you touched the sub's metal plate, the receiver's metal case (including the aluminum front) plus the cable the hum started. Sometime it remained even if you stopped touching it. I disconnected everything and the sub hummed if you touched the cable at the opposite end (the receiver's).

    I rerouted all my cables, video with video, digital with digital, analog with analog all separately, and power cords isolated together from the interconnects (all my interconnects are Monster and MIT). And I went further and isolated the sub's MIT cable from the rest. The problem was gone to the point that I forgot about it. Until today that it happened all the sudden without touching anything, just listening to music. Only this time it's very hard to make the hum show up except by touching the sub's cable at the receiver's end wether connected or not (now, touching the receiver yields nothing, only the sub's metal plate -not always- and the cable at the receiver's end -always-). I do not have cheater plugs, my surge protector is properly grounded with the three-prong plugs, and the sub, as I said, does not have a protector, neither does it have a three prong-plug by default.

    What are my options here? What should I do? Do I have a ground problem? Do I need to put the sub to a surge regulator as the rest? I know the receiver or anything else in the system is not the problem, so, How do I fix this? wait a minute, let me say that again correctly: How do I fix this, cheap? Ha ha ha.

    Thanks folks, thanks in advance.

    P.S. BTW I already have searched my ass off in this forum for topics related, so don't bother, I have a lot of material but no clue.
     
  2. PaulT

    PaulT Supporting Actor

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    I know this may sound stupid, but, have you tried a different sub cable?

    Isolating it and the other cables will do nothing if the cable itself is flakey. Perhaps isolating it has helped slightly because you moved the cable around.

    Can you check the connections by unscrewing the ends? Maybe you have a cold solder joint, broken shielding etc etc.
     
  3. Bob McElfresh

    Bob McElfresh Producer

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    Ok, the metal case and the outer part of the RCA plug are tied to your signal ground.

    When you touch the plug, your body acts like an antenna and injects a 60 hz humm into the signal ground. And remember: the amplifier tries to amplify any difference in voltage between the ground and the center wire.

    This is not a ground-loop, it's noise.

    You must have some high-power equipment nearby, or fluourescense lights, overhead power wires, nearby antennas - something is filling your room with signals.

    The answer is obvious: dont touch the plug.

    You might also consider getting a subwoofer cable with little arrows on it. These cables have one side where the shield is NOT connected to the RCA plug. This would stop noise from injecting into the sub (but you might still have the problem with noise injecting into the receiver).
     
  4. Wayne A. Pflughaupt

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  5. Barton Lynch

    Barton Lynch Stunt Coordinator

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    Well...

    Checked the cable, and the solderings are fine. The cable has arrows indicating the correct flow and it's properly connected, there is a terminator network (a little box with passive equalizers and other energy correcting stuff).

    The cable is not the culprit, because it happened when I touched the metal plate of the sub's amp, and the receiver's metal too, but that was when all the cables where in a "spaggetti-orgy-mess". Not anymore since the rerouting, isolating and ordering of the interconnects.

    Looked for antennas, and there is one for the FM tuner. I correct myself, I touched the cable again and again and nothing happened. I realized that I was barefooted that day (on a concrete floor) and that is why it happened everytime I touched the cable. It does not happen at all with some sort of shoes on.

    I think I'm with Bob on this. Some sort of energy or signal atracction is present. Also all the cables from the DSS dish goes through my room (there are three decoders in the house, one in my HT). The FM antenna might have been doing something because the previous cable mess was with the antenna included. The Sub is in the same outlet as the surge protector by the way.

    Thanks folks, we're getting somewhere here. Should I put a rug on the floor? I am barefooted or with socks all the time in my home. Maybe that is way the problem showed up again.

    Thanks again
     
  6. AaronBatiuk

    AaronBatiuk Second Unit

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    I solved a similar problem by giving some loosly-fitting rca's a little squeeze in a pliers. This made the ground (sheild) connection more secure, and eliminated the hum I was getting. Note that even if you feel resistance when pluggin in or unplugging the RCA, that may just be the center conductor, not the outer (ground) conductor, fitting snuggly. The ground has to be snug and form a good electrical connection as well.

     
  7. Barton Lynch

    Barton Lynch Stunt Coordinator

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    No Aaron, not the metal part of the cable, as it would normally generate a hum at the touch. But at the plug. But now that you mention the "loose" thing, I think that might be it, since it's not at the light touch but at the light rocking of the plug using two fingers. But before the relocation of the cables it WAS at the light touch and at almost everything you touched, which was probably due to the interference of the FM antenna and the "spaggetti-power-cord-mix" that was "braided" with the interconnects. I'm only figuring these things out as you guys tell me stuff.

    Thanks again
     
  8. Wayne A. Pflughaupt

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    Barton,

     
  9. Chu Gai

    Chu Gai Lead Actor

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    a bad expensive cable...rather disturbing though that you'd be able to cause problems walking in your bare feet.
     
  10. Matt_Doug

    Matt_Doug Stunt Coordinator

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    I'm not an expert but i've had similar problems. I turned on my system one day and the sub kicked in with a 90db hum. the sub cable was bad.
    Electricity, whether its low voltage audio video signals or static, high voltage AC or super high voltage lightning, is always trying to return to ground to "complete the circuit" And it will always take the path of least resistance. (which in your case seems to be you every time you touch a conductive surface in your system.) I hope you realize the inherent danger of being a conduit for current flowing to ground.
    Its obvious the path to ground in your system is compromised causing voltage to spill (flow where its not supposed to) and raising the electric potential of your system. If the spill has enough potential you may ground off your system one time, for the last time. Its either a faulty interconnect, a faulty component or a faulty wall outlet. I would disconnect everything including power cords from the wall outlet. Then check for possible life threatening problems first by checking your wall outlets then plug in and interconnect your components with your amp one by one all the while checking for hum.

    Good luck
     
  11. Barton Lynch

    Barton Lynch Stunt Coordinator

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    Thanks folks, helped a lot.
     

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