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Sound engineer help needed!

Discussion in 'Band Management [BG]' started by chris4001asat, Nov 20, 2003.


  1. chris4001asat

    chris4001asat

    Dec 16, 2002
    Toledo, Ohio
    Warehouse Manager : Reverend Guitars
    I'm using an SWR Super Redhead which has its own XLR send on it. We used it on our rehearsal the other night and it worked fine. We set up for our first gig last night, and got a horrible hum on my channel in the mains. Flipping the ground lift switch just made it worse. So I pull out my Fishman Platinum Pro that I use for my upright and use it for a direct box. It sent the signal fine to the board, but the second i plugged into my amp, the hum came back in the mains. Just before we gave up and left, the dj told us that we had our power amp for the mains plugged into the same power as the stage lighting system. My amp was plugged into a seperate outlet. Could this be the problem? The gigs this weekend, any suggestions?
     
  2. chris4001asat

    chris4001asat

    Dec 16, 2002
    Toledo, Ohio
    Warehouse Manager : Reverend Guitars
    bump
     
  3. i'd say it could definately be the problem. i'm no expert though...
     
  4. chris4001asat

    chris4001asat

    Dec 16, 2002
    Toledo, Ohio
    Warehouse Manager : Reverend Guitars
    Bump again:D
     
  5. Petebass

    Petebass

    Dec 22, 2002
    QLD Australia
    There's another possibility. Maybe the sound guy's lead was faulty. They will always swear black and blue that the lead is fine. Don't believe them, they're too lazy to run another one. But it cures the humm 9 times out of 10 so stick to your guns.
     
  6. Phat Ham

    Phat Ham

    Feb 13, 2000
    DC
    Seeing as how you used two different DI's and still got the same hum I doubt the problem is with your equipment. Has the sound guy done anything to try to fix the problem?
     
  7. chris4001asat

    chris4001asat

    Dec 16, 2002
    Toledo, Ohio
    Warehouse Manager : Reverend Guitars
    Strange, the guitar player handed me a 3 prong adapter, and the hum was gone! That's a new one....
     
  8. It sounds like your getting an AC hum due to being plugged into different circuits that aren't wired correctly or isolated from interference. Your rig was probably on one circuit and the mixing board on another. You could also get this problem from power amps plugged into a different circuit. If your plugged into a circuit that has your lights plugged into it, especially dimmer packs, you can get AC hum. It's a tough problem to avoid and correct a lot of times, playing different venues. The only sure way to avoid it is to use a power distribution center that assures all the circuits are wired the same way and are isolated from outside interference.
     
  9. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    Yep. Ground loops have plagued audio setups since time immemorial. Okay, the three prong adapter, that's a clue. There are two possibilities: either the house wiring is bad (which is very likely, the vast majority of the clubs I've played at have bad wiring), or, one of your amps isn't grounded, or is grounded incorrectly. The former is way more likely. You can tell whether an outlet is wired correctly by using one of those little tester gadgets you can get at any Home Depot for about 10 bucks, just plug it into the outlet and it has three little lights that tell you what the wiring's like. But one thing this won't find for you is ground wiring that's not to code and is likely to cause ground loops. For instance, you can have ground wiring tying back to a common point in the building, like a pipe strap or a ground rod, and if it so happens that you plug two pieces of equipment into different sides of the ground, and then connect them together with an audio cable, chances are high you'll get a ground loop and it will result in audible hum. One way to fix this is to plug the amp into the same circuit as the board, so that "ground" means the same thing in both places (or as close as it's gonna get for practical purposes). Another way is to lift the ground on your amp by using a three prong to two prong adapter, but this is slightly dangerous because it means the amp's ground depends on the audio cabling for its connection to the house ground, so this method should only be used temporarily and as a last resort. I'd check to make sure your Redhead is properly grounded, you'll need an ohm meter or continuity checker to test that. If you happen to read about "star grounding" in any of the guitar or amp rags, the same principle applies when you're putting together large audio systems. Try to get the grounds as close together as possible, and keep all the cables as short as possible.