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Buzzzzzzzzzzzzzzzz

Discussion in 'Sound, Music, and Intercom' started by nd925a, Mar 14, 2009.

  1. nd925a

    nd925a Member

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    My csd has an aud with a really screwed up aud....they have a hug rack backstage left that has 6 amps runing to 2 speakers, a digital mackie mixer and 2 wireless handhelds.
    my problem is when i put an external board through the mixer i get a buzzing kind of humm that sounds like to much power running through the speakers, but the handhelds run through the digital fine.....question is how do i fix.
     
  2. Stookeybrd

    Stookeybrd Active Member

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    How are you running the sound from the outboard to the Mackie?


    Balanced? Unbalanced?

    From an Aux, from a Group, from Outputs?

    What does your gain structure look like?



    Also if you fully type out each word, more people can help you.
     
  3. nd925a

    nd925a Member

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    sorry about the short typing....
    i'm putting the outboard in through a port in the back wall of the auditorium labeled mic 3
    gains on the one mic i had to test with was all the way down
    i'm still new so i can't answer your 2nd and 3rd questions
    i can get specifics and pictures soon hopefully
     
    Last edited: Mar 14, 2009
  4. Hughesie

    Hughesie Well-Known Member

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    try to isolate cable issues and provide more details about when it happens.

    For example if you told us it took place during a show while lighting was fading then your issue could be there. But if it is happening all the time chances are the grounding on the cable has come loose or your running the cable near a large electric source such as an epod.
     
  5. Eboy87

    Eboy87 Well-Known Member

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    So, let me see if I've deciphered this correctly.

    You have a PA in your auditorium. Your mixer, which I shall refer to as a console, sounds like a Mackie TT24. Now, your system is fine when run normally, i.e., just the handhelds running through the Mackie.

    You're getting a buzz (which sounds to me like a ground hum, around 60 Hz, 50 Hz if you're overseas) when you plug in another console to yours, correct? That's what I get by reading your original post. Or are you referring to an outboard processor (typically referred to as "outboard"), like an equalizer, compressor, gate, effects processor, etc?

    Is this "mic 3" input in the auditorium getting the output of another console or a microphone? I'm under the impression that another console is plugged into it. If that's the case, (well, regardless if it's a console or not) start unplugging things until the buzz goes away. What is likely happening is that there is a piece of equipment that is on a different circuit than the rest of your PA. Voltage is leaking into the ground on the different circuit, which creates a voltage potential between the two pieces of equipment, as the shield wire (think of it like a ground wire) in the mic cable connects the two, whether it be two consoles, or a console and outboard gear. That shield wire lets the offending gear send voltage down it to the other equipment, which is what creates the buzz.

    Now, you just have to determine whether you're using two circuits or not, and isolate the offending gear. If you're just a student, I would suggest having an adult help you with that part (my apologies if you are an adult). If you find the piece of gear creating the buzz, and put it on the same circuit as FOH (the Mackie and its outboard), your buzz should go away. If it doesn't, then there's likely a different problem. But let's tackle this one first.
     
    chausman and (deleted member) like this.
  6. nd925a

    nd925a Member

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    hughesie
    a) what's an epod????
    b) it's all the time and the port to backstage is in a brick wall
     
    Last edited: Mar 14, 2009
  7. nd925a

    nd925a Member

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    eboy
    when i said outboard i ment an external mixer
    i am a sophomore in hs
    sorry for any confusion
    some local adults are putting on a production in an elementary school where there's noone even close to a td
    the "console" is not a tt24 it is a small 1 or 2 rack space thing with colored bars that move up and down with buttons to do so
    and the external mixer is the only thing plugged in to backstage besides the wireless handhelds
     
  8. David Ashton

    David Ashton Active Member

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    Sorry but you are in way over your head, either get someone in to help you or do some serious reading of the basics of sound systems especially gain structure, you will then be in a position to explain your problem in a meaningful way.Unfortunately your description makes no sense.
     
  9. Eboy87

    Eboy87 Well-Known Member

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    Last edited by a moderator: May 30, 2014
  10. lieperjp

    lieperjp Well-Known Member

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    If you don't want to buy the book, check out the wiki entry on Gain Structure. It will give you an idea about what it is.

    Gain Structure
     
  11. museav

    museav CBMod CB Mods Departed Member

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    There was a time when in all the Mackie/EAW Commercial/EAW continued reorganization within LOUD that products like the EAW DX8 and DX810 were offered under the Mackie label so it may be one of those.

    The first problem may be trying to take a line level output from a mixing console into a mic input. Try a DI box or at least a pad, ideally either with a transformer. The second issue may be a ground loop, as was already suggested try powering the remote mixer off the same power as the rest of the sound system.
     
  12. FMEng

    FMEng Well-Known Member Fight Leukemia

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    This sounds like a classic ground loop. Each console is plugged into an AC outlet, but because of the distance, the grounding connection at each outlet is at a slightly different voltage potential. Inside the consoles, the audio grounds are connected to the AC ground. The voltage difference causes current to flow on the audio cable shield (pin 1 of the XLR connector), which induces noise into the circuit.

    Assuming that the audio output and input are both balanced, you can fix this by making a short, special cable that drops pin 1 at one end. Open up the cable XLR connector and cut the wire that goes to pin 1. Make sure it cannot contact pin 1 or the metal shell of the connector by using tape, if necessary. Label the cable very well so that you know it is a special "ground lift" adaptor, not to be used for microphones.

    Ground loops are a common problem whenever AC powered equipment is spread out over long distances. Lifting the audio shield connection at one end of the cable is the preferred way to fix it.

    Never, ever lift the AC power ground to fix a ground loop. That is an unsafe practice that can get someone killed.

    If the output is unbalanced, then the solution becomes more involved. It might take an audio isolation transformer.

    As for gain structure, what people are trying to get at is that the remote console's line level output needs to drive an input at the main console with the gain set for line level, not mic level. You also want to ensure the input does not apply phanton power. Many consoles have a mic/line switch to change the gain and turn off the phantom for that channel.
     
  13. nd925a

    nd925a Member

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    do you mean at the end that the mic imput on the backstage mixer is pushing phantom power to the external mixer??
    here's somthing else i just remembered too: the sound is made whenever the external mixer is on...it doesn't get louder or softer if everythings at zero......when i push for feedback it just gets louder
    and the backstage mixer looks like a digitalized eq
    sorry i forgot that info earlier
     
  14. Eboy87

    Eboy87 Well-Known Member

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    No, in this case, phantom power has nothing to do with it. At this point, you're in way over your head. That Mackie unit you refer to, I don't think that's a mixer at all. I think it might be their new digital equalizer. Does it look like this?

    [​IMG]

    What's happening is with the electrical ground, the 120V AC line. It sounds like you have a portable console that plugs into your system. What's happening is that it's most likely on a different AC circuit (different plug) than the rest of the PA system. What's happening is there's electricity leaking down the shield of the cable connecting the console to the PA because there's a voltage difference between the two grounds. We're talking under 5 volts here (hopefully). If you can get the console on the same AC circuit as the rest of the system, the buzz should go away.

    However this line makes no sense to me:
    Are you saying there's feedback as well? The first part lends credence to the ground loop issue. I have no idea what you're talking about with pushing for feedback.

    I think at this point you need to have someone qualified to come in and take a look at your problem. Where are you located?
     
  15. nd925a

    nd925a Member

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    yes that is the thing backstage
    when is say feedback i mean i turn the mic gain all the way up and the slider for the mic and master all the way up... at the hs that gives me feedback....at the elementary school the buzz from the different ground outlet just gets louder
     
  16. howlingwolf487

    howlingwolf487 Active Member

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    As others have said, this definitely sounds like a grounding issue.

    I think that you should try running the AC power for the "external mixer" from the same outlet(s) that the other mixer is plugged into. Mixers don't draw a lot of current unless something is wrong, so you shouldn't have to worry about tripping a breaker. Use a long extension cord if you need to; make sure all 3 prongs are intact. That will tell you if the hum/buzz is being caused by the outlet you were plugging into.

    If the hum/buzz continues, there is something wrong inside the mixer. You should then get it looked over by a certified tech (wherever you bought it from, mayhaps) and let them try to find out what the real problem is.

    Best of luck!
     
  17. museav

    museav CBMod CB Mods Departed Member

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    As I noted, the EAW DX810 (Mackie - dx810) or DX8 (Mackie - dx8) matrix mixers look similar to the Mackie digital EQ. The DX8 and DX810 were originally Mackie products that with the LOUD Technologies corporate changes got moved under the EAW Commercial name and are now EAW products. Here's the EAW DX810, same basic box as the Mackie DX810 but with a different brand name:

    [​IMG]

    So if the system is a few years old it could be the Mackie version of the DX8 or DX810. Knowing whether the inputs are line or mic level and changing a mic input to line level requires accessing at the rear of the unit. There are separate mic and line connections and a trim knob on the rear panel for each input.

    I think the problem is likely a ground loop exacerbated by the excess gain from running a line output of a temporary mixer into a mic input of the installed system. A transformer based DI or pad may fix both.
     
    Last edited: Mar 16, 2009
  18. Skinny

    Skinny Member

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    I agree that you should have somebody qualified take a look. The problem doesn't seem too complicated, so it should be solved easily by somebody who knows what they are doing.

    This is what we get paid for.

    Skinny
     
  19. nd925a

    nd925a Member

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    Thank you all for the great advice i think mybe all the cables i tried were bad that the school owns
    if it's not the cable then i will talk to a local guy i know who can help
     
  20. Eboy87

    Eboy87 Well-Known Member

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    Call someone qualified. The general consensus is that it's an electrical issue, not the cables. Call someone first, so things don't get worse.
     
    Last edited: Mar 19, 2009

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