Dreaded Hum in new set up with dedicated line

Discussion in 'Home Theater Projects' started by Gary Hunter, Mar 19, 2004.

  1. Gary Hunter

    Gary Hunter Agent

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    The theater is nearing completion and I've got the equipment installed. Unfortunately I have a severe hum/buzz in my main speakers.

    I am using mono amps, each with a dedicated 20A line. When I turn on the R amp a very loud hum/buzz is present in both R and L channels. When the amp is disconnected from the interconnect, the hum goes away. I switched from single ended to balanced interconnect but that didn't cure the problem. All the other a/v equipment is plugged into a another dedicated 20A circuit.

    When I plug them both into the same outlet the hum goes away. So it seems that I have grounding issue. I don't want to plug them both into the same outlet because that defeats the purpose of the individual dedicated lines.

    Any thoughts about what needs to be done to cure this problem?

    Gary
     
  2. Philip Hamm

    Philip Hamm Lead Actor

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    And that purpose was..... ? [​IMG]

    You need the curcuit checked and grounded by a qualified electrician. Otherwise I'd recommend a simple ground lift device, I've had great luck with Ebtech Hum Eliminators but I'm sure they would not agree with your audiophile sensibilities.
     
  3. Gary Hunter

    Gary Hunter Agent

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    20A of current to each monoblock.

    Thanks for the info. This is a new construction with all the wiring done by an electrician. I'll probably call him to see if he can solve the problem if it is in the electrical wiring versus the components.
     
  4. Philip Hamm

    Philip Hamm Lead Actor

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    Yes, do that, call the electrician, they should be able to do warrantee work if they find a mistake, or deal with the warrantee work on any failed components.
     
  5. Pete H

    Pete H Stunt Coordinator

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    I have been where you are. I wish you better luck than I had. Below is a quote from a guy that makes a lot of sense to me. I have not tried it myself.

    "We used one heavy ground wire for all four circuits with pigtails right by the outlets for ground. I also plug my main source into the same outlet as the preamp which made a difference."
     
  6. Gary Hunter

    Gary Hunter Agent

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    Pete,

    Then have you not remedied your hum?

    I know that the hum/buzz is only present when the pre-amp is plugged into the right channel amp only. If I plug both channels in to one amp in stereo, or as I said before, both amps into the same outlet, their is no buzz. The center and side/rear channels do not have any buzz. I plan to disconnect all my source components, etc. to see if it is the pre-amp or another culprit. I believe the only components plugged in via interconnects are the CD and DVD player. I have another DVD player and D-VHS which are connected via toslink so they should not be the problem.

    At this time I do not have any satellite/cable connected to the system by the way, so it's not the infamous coax cable source.


    Something else I just thought of is to plug both amps into the outlet that the R amp has been plugged in to and see if the buzz returns then. If so, then the problem may be grounding differences between those two outlets possibly.

    Thanks for any and everyone's ideas.
     
  7. Adam Gregorich

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    Have your electrician make sure both circuits (and any other HT circuits) are on the same phase.
     
  8. Wayne A. Pflughaupt

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    What Adam said. It would be typical for an electrician not familiar with audio protocol spread two new circuits across both service legs.

    Regards,
    Wayne A. Pflughaupt
     
  9. Gary Hunter

    Gary Hunter Agent

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    Thank you everyone.

    Over the weekend I have had time to experiment with the equipment. I will be calling my electrician today to discuss the issue with him.

    I have discovered that cheater plugs eliminate the buzz completely. Also, if I run an extention cord from the older part of the house to the new addition, (different breaker boxes), the buzz is also eliminated. No component seems to matter except that the pre-amp must be connected for the buzz to occur.

    So I'm thinking that the wires are out of phase or not on the same ground. What is required to unify the phase, just out of curiosity. Also, would having a separate bar for ground and neutral help (I don't know if I do now or not as I didn't open up the box but have heard that it is not uncommon to wire the neutral and the ground together on one bar).

    Thanks,

    Gary
     
  10. Chris_HA

    Chris_HA Agent

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    Most new breaker boxes are setup so that every other breaker is on the same phase. All you should have to do (once main power has been disconnected) is move one of your new breakers down or up one space in the box.

    The neutral and the ground should be wired to the bus bar and do not need to be changed, unless you need to route them to keep them from being kinked or bent when moving your breaker.
     
  11. Gary Hunter

    Gary Hunter Agent

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    AAAhhhh,

    OK. I'll take a look at it. My electrician is out of town until next week so I have a little time to investigate things on my own until then.

    Thanks!!
     
  12. Gary Hunter

    Gary Hunter Agent

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    How about side to side?

    My box has odd # breakers on left, even on right.

    Are you saying that breakers 1 and 5 and 9, etc. are the same phase and 3 and 7 and 11 are opposite? What about the evens? Are 1 and 2 the same phase?

    Sorry for the questions, just want to be certain before taring into my box.
     
  13. Legairre

    Legairre Supporting Actor

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    I had the same problem with two amps on seperate dedicated circuits. I simply ran a peice of left over speaker wire from a screw on the chasis of one amp to a screw on the chasis of the other amp and the hum went away. If I remove the wire it comes back. Also don't use a cheater. If anything ever happened and you touched the amp you could take a nasty hit and become the ground. The ground is there for a reason, don't remove it.
     
  14. Adam Gregorich

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    Gary-
    Without knowing the exact make and model of your fuse box, I am assuming it is how you have described it: 1, 5 & 9 are on one phase and 3, 7, and 11 are on another phase. Find your breakers for your two dedicated circuits and see if it appears that they are on the same phase or not.
     
  15. Gary Hunter

    Gary Hunter Agent

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    Thanks again all.

    The dedicated lines are on 5 and 7 so that may very well be my problem. I may try that wire trick, Leggaire. The electrician is coming Monday should I not get it remedies before that.
     
  16. Chris_HA

    Chris_HA Agent

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    Here is an annotated picture of my box from this morning. I hope this helps explain what I mean by every other breaker.

    Click here for my breaker box picture

    What I would do is to remove the cover from the breaker panel to see how yours is setup. Feel free to turn off the main power if you feel safer, but unless you touch anything inside, you should be fine.

    Having two dedicated lines is fine, but the have two dedicated lines across phases can be dangerous. If you have a fault in one or both pieces of equipment that are cross connected (like your amps that share a common preamp), you run the risk of bridging the two circuits (like a stove, dryer and A/C unit) and having LIVE 240V instead of live 120V. I'd rather take my chances with the 120V on the same phase.
     
  17. Gary Hunter

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    Chris,

    Thanks for the picture. That helps a lot. I know that the dedicated amps are on opposite phase because they are right above/below each other. My power conditioner is on a 220V double pole breaker that spans two spaces so I'm not sure exactly how that effects the phase.
     
  18. Gary Hunter

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    All of my source equipment and pre/pro is plugged into the power condiditoner as stated above. All amps are plugged into their own dedicated line.
     
  19. Adam Gregorich

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    I'm not sure what you mean when you say your power conditioner is on 220 . Is it a whole house power conditioner? It doesn't seem right that you are feeding audio equipment off 220. I still think you problem will go away if you (or your electrician) switch one of your dedicated circuits to another breaker so they are on the same phase.
     
  20. Gary Hunter

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    Adam,

    I have an Equitech 3Q, which provides balanced AC for the source components. It utilizes a dedicated 220V line. Check out their website for more info @ www.equitech.com. Hopefully the electrician will agree and change one of the breakers so the phase is consistent. I would do it myself but don't want to void any warranty, burn down the house, etc. [​IMG]
     

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