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Ground loop mystery...ideas?

Discussion in 'Amps and Cabs [BG]' started by tornadobass, Jul 4, 2004.

  1. tornadobass

    tornadobass Supporting Member

    Nov 20, 2000
    Iowa City, Iowa
    Endorsing Artist: Black Diamond & SuperSensitive strings
    I did an outdoor gig today and couldn't solve a ground loop hum problem.

    Here's the particulars:

    * Power supplied by large generator.
    * DI from SWR SM-400S to PA via XLR.

    Hum was reduced with the amp's DI ground lifted, but never went away completely in either position.

    We ended up running an outboard Countryman DI off the amp's line out and that took care of the problem.

    Is it possible that there was a wiring or grounding problem with the generator's electrical output? The sound guy put the amps on a different outlet than the PA system, but it was all from the same source. I know that I've had to lift the amp's ground much of the time I've used it...any chance something isn't quite right with the built-in DI??
  2. daddyo


    Jun 9, 2004
    British Columbia
    I would say the magnetic field off the rotating generator is the culpret.
  3. xyllion

    xyllion Commercial User

    Jan 14, 2003
    San Jose, CA, USA
    Owner, Looperlative Audio Products
    Yep, this would be my guess as well. When I plug in at my friend's practice studio, I have horrible troubles with buzzing, but everywhere else I have no problem at all. If you have a noisy environment, it may be next to impossible to clean up the noise.