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Guild preamp question..

Discussion in 'Pickups & Electronics [BG]' started by baba, Apr 8, 2009.


  1. I need some help troubleshooting the preamp in my Guild. Here's the deal...

    Without a battery, it sounds GREAT passive. If I flip the bottom switch up (with no battery), which I think is a active/passive switch, the signal drops to about 50% but is still there. Switch up or down, the two little (I assume) preamp tone knobs don't do a thing.

    With a battery, it sounds the same (GREAT) passive. If I flip the bottom switch up, there is NO signal. Again the two little assumed preamp tone knobs do nothing.

    I'm assuming the preamp is shot. Any other tips or trouble shooting I could do to confirm this or try to correct the problem? I'm guessing yanking the pre and hitting the hidden side pots with Deoxit couldn't hurt...

    Here is the control layout and pre cavity. The top switch is pickup selector, the middle one is maybe a coil tap, I think the bottom one is a active/passive switch, and I think the little knobs are active tone only.

    IMG_3640.
    IMG_3657.
     
  2. JTE

    JTE Supporting Member

    Mar 12, 2008
    Central Illinois, USA
    None of that looks stock for any Guild I've ever seen, except the bridge. The PUPs, the metal rings, and the whole control set up all seem to be some sort of after-market thing.

    If it was mine, I'd take the knobs and all the nuts off the controls, and extract that PCB to see if I could find loose wires, cracked traces, or other damages to the board.

    jte
     
  3. It's all original for sure. It's a B-402A...very rare. Thanks, I'll check for board damage as suggested.
     
  4. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    It's good to see they put the op amp on a socket. If you don't see any problem connections, I'd try popping in a new op amp.

    That's a cool bass. I've never seen that exact model.
     
  5. JTE

    JTE Supporting Member

    Mar 12, 2008
    Central Illinois, USA
    Tell me more! I was a Guild dealer from 1977- 1988 and the only bass I've ever seen with a pre-amp in it was my Pilot Pro (I got it after I left the store). It had a Mighty Mite pre-amp BTW. If fact, I think I still have the pre somewhere in my parts boxes. I yanked it out after a few years as I figured the EMGs would sound better with no preamp instead of a cheap noisy one...

    I love Guilds! Criminally under appreciated at every step, lousy marketing, and bad luck conspired against some of the finest fretted instruments made.

    jte
     
  6. Bear with me here...I'm not electronics savvy. Is the op amp the little black dealio on red under the bridge pickup pot? Is that what actually juices the signal?
     
  7. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    Yes.
     
  8. JTE

    JTE Supporting Member

    Mar 12, 2008
    Central Illinois, USA

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