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Ground Loop Issues

Discussion in 'Sound, Music, and Intercom' started by TheAngryFedora, Jun 28, 2006.

  1. TheAngryFedora

    TheAngryFedora Member

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    Hello there- I'm wondering if anyone has any advice about this:

    I'm working on a musical at the other high school in my town this summer. We're running something like 16 lav's, with the recievers stage right. They work fine, apparently, at least that's what I've been told by the people returning from last summer, we'll be doing extensive testing I hope... But, the main issue (aside from some annoying dead spot/slight interference on a couple of the packs that we'll fix) was that the recievers weren't being run off of the same circuit as the rest of the equipment. Therefore it created a ground loop. I don't know enough about electronics to really say with certainty that I have just used that term properly, but oh well.

    Is there any way to fix the insufferable hum that we get from this? Something that we can plug into the wall, and then plug the rack into? I know that I've seen some equipment like that somewhere, I just have no idea where. Any advice is appreciated.

    Thanks,
    -Ben
     
  2. audioslavematt

    audioslavematt Active Member

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    The only two options I can think of are a.) lift the grounds (not advisable in most situations) b.) run some really long extension cables to get them on the same circuit. I would put all the recievers in power strips so you don't have to run as many.

    I have the same problem with our house mix location. It's not tied in with the rest of the system (even though the wiring is there), so I normally end up running a 75 foot extension cable out the window.

    Edit: Also, stay away from the hum eliminators. Those will screw with your EQ on the mains. I forgot about islation transformers. http://www.procosound.com/tradetoolsindex.htm#isolation There are also some that are much smaller, about the size of an XLR plug. They will fix your problems a lot of times.
     
    Last edited: Jun 28, 2006
  3. mbenonis

    mbenonis Wireless Guy Administrator

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    You are indeed using the term correctly, Ben. I would offer the same advice that Matt offered; that is, run an extension cord over to the receiver rack (make sure it is properly rated, of course). You might also consider moving the receivers to the mix position if the rack is portable (this will give you the added benefit of being able to monitor RF during the show).

    For the long term, you should consider talking to the building maintenance folks to see why there is such a large voltage between grounds in the building, or to see if you can get a new receptacle by the rack from the same branch as the rest of the audio equipment.

    Good luck, and let us know how this turns out and if you have any other questions.

    PS: Out of curiosity, what wireless systems are these?
     
  4. TheAngryFedora

    TheAngryFedora Member

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    Thank you very much for the advice. A couple of questions/points-

    1) What is wrong with a ground lift? What are the drawbacks of such a device? Is it dangerous? Unreliable?

    2) Extension cords may be an option, but the board is in the back of the house and we would be gaffing the cable down in one of the most heavily trodden-upon areas of the theater. It may be worth it, though. It would be FAR too much to run the cable all the way through the catwalk, about 150 to 200 feet, and it would then be running right next to our snake. Not a good thing.

    3) Building maintenance and the likes will be pretty useless (thank you for the suggestion, though.) Some of the horror stories that I've heard about this building have been incredible. They're knocking it down in a year or two and building a new high school. The auditorium is pretty big for a high school auditorium, and most of what is installed has been installed by generations of techies. No one knows what the hell happened when they built the building, except for what they have figured out.

    For example, they have figured out that a random lightbulb stage right is wired in series with some of their dimmers. So, if that blows, the power goes out.

    There are vents in the school that go nowhere. Literally. They just sit there, doing nothing, no fans, no pipes, just sitting there. There are other potential vents that, if you look above the ceiling tiles, start, go three feet, and stop. Again, going to nothing.

    Their other theater, "Little Theater," which is a black box, is somehow wired to the emergency generator. They have no idea how, but when the power was off one evening and their lights (or some of them) were still on, they figured it out.

    Their auditorium was supposed to be built in one direction, so that the Little Theater booth and the auditorium booth would be connected, but someone lay the plans out the wrong way on the table and they started building it in practically the opposite direction. They lay the foundation before someone told them they screwed up.

    They were supposed to have a massive door between the shop and the stage. That never got built. They put the pipes in first or something, so they have the top of what should potentially be a door just randomly sitting in the brick wall backstage.


    There are more, but I haven't been there long enough to really retain the stories. They're told all the time, though. They like talking about how messed up their theater is.

    The city is pretty corrupt. They're giving the same contracter who totally messed up the renovations on my school the contract for the new school. It's a little frightening how incompetent these people can be.

    Oh well.

    4) We are using Sennheiser E100's I think. I'm not totally sure. We may also be using a few Shures, we're taking a two hour trip to go and see the guy who will lend them to us next week.

    They are in racks with power strips built in, and we're using three or four racks I believe. So, it shouldn't be too big of a problem to run those up to a couple of outlets somewhere. Hopefully running all of those into one or two outlets won't blow out the power, but we'll find that out when we hook them up.

    5) Moving the racks would certainly be ideal. I would like to be able to fix things on the fly, moniter the RF and AF levels, not have to run down to the stage or yell at somebody every time I want to change something. But, the issue is the reception. Big auditorium, lots of interference, dead spots on the stage- that, and the breakout box is down there. It's easy enough to get a new snake, but we really have no money left for sound (buying one passive and one active EV speaker, a driverack 260, and several countryman elements.)

    Thanks for your time
    -Ben
     
  5. jbeutt

    jbeutt Active Member

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    Ben,
    The easiest and safest fix for now is to get yourself an iso-transformer between your racks and FOH. This will essentially decouple the electrical signals, while maintaining them. These are easy to get from any pro-audio supplier.

    The danger of removing the grounding pin from your equipment is that should wires within said equipment come loose, electrifying the equipment, that "wild" electricity will flow through you. A ground lift, in itself, is not dangerous when used properly. However, for audio applications, using it properly won't fix the hum. It's the improper use of a ground lift that becomes a danger, but fixes the humming. The use of ground lifts is unsafe and extremely poor audio technique and should be illegal for the dangers it poses.

    A hum in the system, however, is not necessarily a ground loop issue. Pin 1 problems are another culptit of noise injection along with numerous others. A pin 1 problem is an equipment fault (which I won't go into).

    When troubleshooting a problem like this, find out 1st what specific piece of equipment is making noise. If only one receiver is, equipment fault is more likely than a general circuiting(ground-loop) problem.

    If the problem is indeed a ground loop, just put iso-transformers on your signals or your power. One of those plug-in power buzz "eliminators" does the same thing to the power that a signal (xlr) iso-transformer does. It's the same either way. Before you go off and buy anything though, make sure that a ground loop is the problem. Bring your racks up to FOH, hook them up, and see if the buzz is gone.

    As for "dead" spots in your wireless, this is really just from either poor wireless "design" (bad frequency selection), intermodulation (similar issue) or inadequat reception which simply requires upgrading your antannae placement and distribution setup.
     
  6. Footer

    Footer Senior Team Senior Team Premium Member

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    Well as far as using a ground lift (otherwise known as breaking off the ground pin) goes yes it will sometimes work, but you run the risk of blowing equiptment or hurting yourself. THe grounds are there for a reason, to keep a shortest path to ground. First think I would do in your situation is to find out what breaker boxes are feeding the rack and the FOH. After you have done that find out if the feeds to the boxes are single phase or 3 phase. If they are three phase try to get both racks run off the same leg of power. This will in esence put them on the same circuit.
     
  7. jbeutt

    jbeutt Active Member

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    The circuit isn't rrrreally the problem. Yes, generally it's good to have interconnected equipment on the same circuit, but don't misunderstand the problem. Ground loops occur quite easily on the same leg and even the same circuit.
    In a well designed electrical system, different circuits should have the same ground potential. All grounds and neutrals must be bonded at the service entrance. Obviously, this is not always true by a long shot and putting equipment on the same circuit CAN fix the problem, but likely might not. Consider that in some electrical cables, specifically romex and industrial cables, ground is not independantly jacketed and so it is very easy for it to bond to the building at places it shouldn't. This definitely goes along with what you said about your school. Even many professional theatres are not conscious enough to prevent these problems, like varying ground voltage.
     
  8. AVGuyAndy

    AVGuyAndy Active Member

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    Hurting yourself? You have got to be kidding. You can KILL youself lifting grounds.

    All of you suggesting this really need to think before opening your (virtual) mouth.
     
  9. mbenonis

    mbenonis Wireless Guy Administrator

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    Absolutely true - lifting grounds is a big no-no, and is illegal in most municipalities because you CAN seriously injure or kill yourself.

    I think in this case the best solutions would be to either run a properly-rated extension cord to the rack, or move the rack to FOH. Ben, you mentioned that you're having interference problems with the mics - would you mind posting the frequencies in use here once you know them? We can work with you to make sure that your frequencies don't interfere with each other or with local TV stations.
     
  10. BillESC

    BillESC Well-Known Member Premium Member

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    We carry several of these in our gig box and they work perfectly.

    [​IMG]

    The Hum X filters out unwanted voltage and current in the ground line that cause ground loop hum while simultaneously maintaining a solid, safe ground. You no longer have to run your audio signal through any type of filtering which can result in loss of volume, tone or both. Some devices simply remove the ground, which is never safe! Simply place the Hum X on the end of the power cord of the equipment that has a Ground Loop and plug the Hum X into any standard 15 amp outlet. Ground Loop is gone and audio signal remains intact. Easy to use, easy to install and completely effective! The Hum X is the safest way to get rid of ground loop hum.
     
  11. audioslavematt

    audioslavematt Active Member

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    Do you sell those Bill? I'd be interested in getting a few.
     
  12. Andy_Leviss

    Andy_Leviss Active Member Premium Member

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    The HumX is potentially VERY dangerous if it fails. Read the review at Harmony Central for details:

    http://www.harmony-central.com/Effects/Data/Ebtech/Hum_X-1.html

    Short version (and please do read that page for the "why"), if one of the components in it fails, it could open up the ground. The HC review sums it up as saying, "With the lack of any safety agency approval I would be hesitant in using this where myself or my company would be liable for injury. If you are at home and use ground lift cheater plugs then this would be a safer alternative."

    --A, who isn't going to trust his life, butt, reputation, or those of his bosses and clients, to it based on that info
     
  13. TheAngryFedora

    TheAngryFedora Member

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    Hey-

    As far as frequencies go, we're about ten or fifteen minutes outside of Boston. So, it's pretty much an orgy of TV and Radio stations out here. We've been setting up the system early so that we can really get started selecting frequencies and spend some time tweaking.

    We may get ahold of a scanner, which would allow us to really test the area. I'll get the zip code of the school and post it, though.

    By the way, there was a pretty interesting discussion on the Theater-Sound Listserve about the Hum X. They came to about the same conclusion that this thread did. It sounds nice, but it's potentially just as dangerous as a ground lift.

    -Ben
     
  14. Andy_Leviss

    Andy_Leviss Active Member Premium Member

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    Uh, it IS. It's most certainly a violation of electrical code, at least here in the US.
     
  15. BillESC

    BillESC Well-Known Member Premium Member

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    "The HumX is potentially VERY dangerous if it fails."

    As is EVERY piece of electrical equipment. It is better than lifting the ground.
     
  16. Andy_Leviss

    Andy_Leviss Active Member Premium Member

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    Yes, but not every piece of equipment is intended to provide protection against other downstream failures. The idea of a very realistic potential point of failure that defeats the entire purpose of a safety device just scares me, especially when said device isn't rated by any independent safety organization (most likely for that very reason).

    Yeah, it's better than lifting the ground, but one could likewise argue that manslaughter's better than premeditated murder. Doesn't make either a good thing.

    If it were the only solution to the problem, it might be one thing, but there is a right way to fix a grounding problem. This is not it.
     
  17. TheAngryFedora

    TheAngryFedora Member

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    Well said.
     
  18. BillESC

    BillESC Well-Known Member Premium Member

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    Having been involved with theatrical production since 1963 I am well aware of the correct way of eliminating ground loops. However there are situations where the correct way is impractical if not impossible due to the physical nature of the venue or time constraints, etc.

    The Hum X is simply a tool that an educated technician might want to have in the tool box should the need arise.
     
  19. mbandgeek

    mbandgeek Active Member

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    This is exactally what the website says

    That is what gave me the feeling of buying 3 million of these

    subliminal message?!?!?
     

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