2nd amp earth loop hum?

Discussion in 'Amps and Cabs [BG]' started by Spike, Sep 26, 2000.

  1. When slaving to a second amp and cab I am getting the dreaded mains hum.
    Tried links from send to return, DI out, tuner out and sub out, both to the return and pre-amp inputs of 2nd amp.
    Also get it with my Ric o Sound kit direct into the two amps. (with no amp to amp loop connection)

    The only way I have found a way around this is to disconnect the earth wire from the second amp, although I’m not sure how safe this is.

    BTW this is UK 220-240 volts AC, and may not be a problem in the U.S.
    Does anyone know if disconnecting one of the earth (ground) wires is ok providing the main amp is earthed, or how I can solve this problem?
  2. jfsjbb


    Aug 29, 2000
    There are some possible solutions for your problem:

    1. You cut the ground wire on <B>one</B> side of your patch cables.
    2. You use a DI-box with groundlift. (As these thingies aren't really expensive, it's well worth buying one or two, they can really losve some problems).

    I'd prefer solution 2, for messing around with the ground connection can be hazardous if you're not totally aware of what you do.

    Hope this helps
  3. Thanks for your help jfsjbb,
    I've got a Raven Labs PMB-1 with a ground lift, but I still get the hum using that.
    A store told me that as long as I make the loop connection before powering up it is ok to have the second amp without an earth. Must admit that I’m not too happy about doing this. I'll try cutting the ground wire on the patch cable.
  4. jfsjbb


    Aug 29, 2000
    Remember to cut it only on <B>one</B> side of the patch.

    I hope this "graphic" will help (top line is Ground wire of the patch cable, left and right are the 1/4" plugs, bottom line is the live wire, x is where you cut.)


  5. Thanks jfsjbb,
    Really appreciated.