Ground Loop / Hum with undersaddle pickup - HELP!

Discussion in 'Acoustic Instruments' started by eugewong, Jun 23, 2008.

  1. eugewong

    eugewong Member

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    Hi all,

    I've got a B-Band UST (forgot the model, it's got a battery, but no other controls, just a preamp as a part of the endpin itself) installed in my Guild acoustic and I've never had any problems with this setup.

    But at this 1 particular gig that i do sometimes, it picks up a terrible hum.
    I tried all kinds of combinations ( different cables, with and without the DI, different DI ) and the hum is always there at this spot. I also tried a different DI with a ground lift, and although there was a very slight improvement, the hum was still there, and prominent.

    However, the hum will go away when I :

    1) move about 2-3 feet off the stage
    2) touch my DI box (LR Baggs ParaDI) and the strings at the same time.

    For the record, the other guitar player was using a mid-end Ibanez acoustic with onboard preamp/electronics and it was totally hum-free.

    Any suggestions on how I can overcome this problem?

    I'm thinking the B-band wasn't installed properly or the B-Band is too sensitive to this particular venue's electrical system/Radio waves/lights?

    Any help or suggestions would be great! Thanks in advance!
     
  2. in a little row

    in a little row Member

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    if it only does this at that one gig, its likely the power supply in that club reacted to your setup...lights maybe...and prolly the bband making noise rather than the DI, sounds like its not grounded right

    are you running phantom power with your PADI?
     
  3. eugewong

    eugewong Member

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    Hi,

    Yes, I was running phantom power for the PADI.

    I also ran,
    1) straight to the board via guitar cable
    2) via passive DI to XLR, ground lift down
    3) via passive DI to XLR, ground lift up

    All gave me hum.

    Only combination I didn't think to try was PADI w/ battery and no phantom.
     
  4. mcdes

    mcdes Member of no importance

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    i just had a d-tar timberline installed in my guild and it made an almighty hum, yet dissapeared when i touched anything metal in the line, incuding MY baggs para-di.

    i had to use it, and since it was a ground loop hum i tied cable round my stomach and the other end to the end jack!(no one could see it, dont laugh!) stupid i know, but it had to be done and it worked.

    the next day i took it back and there was a fault and also a bad solder.

    works a charm now.
     
  5. mcdes

    mcdes Member of no importance

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    oh, and i tried all the exact same things as you too before i tied the cable to it.
     
  6. eugewong

    eugewong Member

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    I should've thought of using my stomach! I was THIS close to taking of my shoes and keeping a toe on the ParaDI !! :D

    So just to check, there was a fault and a bad solder with the pickup? Or the Cable?
     
  7. walterw

    walterw Gold Supporting Member

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    it's usually a problem with the shielding on undersaddle pickup elements themselves.

    since touching the cable plugged into the guitar makes it go away as well, one emergency fix is to run a guitar string around the output jack and thread the other end between the saddle and the bridge pins underneath the strings. that way,since the strings are now grounded, touching the guitar's strings will kill the hum.

    many years ago (when i had guitars but no money to fix them right), i rigged up 2 brass bridge pins on my E strings with ground wires soldered to them from inside the guitar, and ran a strip of copper shielding tape on the back of my headstock between the tuning keys to ground the strings and make the hum go away.

    now you can get a thin brass plate with six string holes in it from stewmac that sits inside on the bridgeplate, and ground it to acheive the same goal. taylor does this on their new version of the ES system.
     
  8. mcdes

    mcdes Member of no importance

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    it was def in the preamp on board, not the cable.
    and he said it was a faulty part as well as a bad solder, all in the preamp.

    i thought d-tar wasnt supposed to be too bad...... but hey, sounds good now with the higher output.
     

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