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Effects loop hum... Grounding issue?

Discussion in 'Amps and Cabs [BG]' started by BassFromHeaven, Jan 7, 2006.


  1. BassFromHeaven

    BassFromHeaven

    Jan 7, 2006
    Hello everyone,

    I've been a long time lurker but this is my first attempt at posting, and unfortunately, I have a problem I was somebody could help me with.

    I have a GK 2001RB amp that I've been having some hum problems with for awhile now, and I think I've finally tracked it down to a grounding issue with the effects loop. When I plug in my rack effects it creates a hum, and that hum disappears when I unplug the effects. I first beleived that I may just have dirty effects, but I get the same hum sound with no effects plugged in, but with just an XLR cable plugged into the Direct Output, and the Ground Lift putton not pressed in. When I press the ground lift button in the hum goes away, but if I plug the rack effects back into the effects loop, the hum comes back.

    I talked to a few local technicians around where I live and they reccomended I try some sort of grounded, schock resistant screws to use in my rack. Has anybody heard of a product like this, and does it actually work? Or would a shock resistant rack be my best bet at solving this problem?

    I can attach an mp3 file of what the humming sounds like if I need to, but I figured most people would already know what a bad ground hum sounds like.

    I know there are some incredibley knowledgable bassist/electricians on this site, and I would love it if one of them could help me with this headache of a problem.

    Thanks in advance for any help I might receive.

    Michael Bishop
    Live From Heaven
    www.livefromheaven.com
     
  2. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Try input/output cables with the shield disconnected on one end, possibly just one will do it but likely both will have to be that way.
     
  3. BassFromHeaven

    BassFromHeaven

    Jan 7, 2006
    Sorry, I also should have mentioned that this happens with nothing plugged into the input.

    After reading another post about Metal-to-Metal contact I discovered that the hum goes away if I unscrew all of my effects from the rack and lay them on the floor. So now I'm interested in hearing if anybody has seen "isolation" rack screws, or has made some sort of rubber sleve that protects the metal-to-metal contact. Or is this why people buy isolation racks?

    Somewhat confused,
    Michael Bishop
     
  4. JimmyM

    JimmyM Supporting Member

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Try using the plastic washers from the rack screws to insulate the rack effects from the rest of the rack. If that doesn't work, you can try Humfrees, but in my rack, just using the washers worked.
     
  5. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Ground loops have nothing to do with the input, so that's normal. Ground loops occur when devices have more than one ground pathway between them. In your case one pathway is via the chassis/rack, another is via the shield on the cables. You have to remove one of those pathways.