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DI Box hum

Discussion in 'Amps, Mics & Pickups [DB]' started by Muyy, Nov 12, 2010.


  1. Muyy

    Muyy

    Sep 4, 2009
    Orlando, Fl
    I recently got an Engelhardt ES-1 upright and had a Barcus Berry insider pickup installed. I am using a Tech 21 Sansamp bass driver as a preamp into either my SVT classic head or my Peavey TKO115. My problem is I just get a hum on both amps, I dont really think im getting a good signal from the pickup. I tried messing with settings, more volume on the DI, more volume on the amp, more EQ on the DI, several different combinations. Nothing works. I just get a hum and I dont really hear any amplification happening. Is it because of a grounding issue? Is the Sansamp not good for vibrational pickups? All help is appreciated.
     
  2. Ric Vice

    Ric Vice Supporting Member

    Jul 2, 2005
    Olivette, Missouri
    Muyy,
    From what I read the Barcus Berry Insider is designed for acoustic guitar. If I'm right about that then that may be your problem right there. It sounds like you have a bad ground or the sheilding of the pickup is faulty.
     
  3. Muyy

    Muyy

    Sep 4, 2009
    Orlando, Fl
    I know the insider was meant for acoustic guitars, but it came recommended from my usual bass repairman and he assured me it gets the job done. The thing is, he said after he installed it, he hooked it up and it sounded great. So either im doing something wrong or it broke on the way home. There isnt a ground on the power supply of the sansamp, which may be the problem. Has anyone else tried using a sansamp with an upright? maybe they only sound good with magnetic pickups, not vibrational
     
  4. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    I'd start by trying it without the SansAmp. As it turns out, the classic SVT (if the schematic hasn't changed since 1972) has 1 MegOhm input impedance, which should be sufficient for a piezo pickup.

    If it's still not happening, then you have to suspect either the pickup or the cabling. I don't know how many times I ruled out a cable problem in my mind, only to discover after much fussing around that the problem was my cable.

    As for not having a grounding plug on the SansAmp, that should actually be a good thing, because it eliminates a possible ground loop.
     
  5. Muyy

    Muyy

    Sep 4, 2009
    Orlando, Fl
    alright, i can get a sound on the amp, if theres no preamp, and if someone is grounding the connection with their fingers by holding right where the cable connects to the input of the pickup. Otherwise there is too much hum to turn it up loud enough to get a signal, so I guess that means its a shielding issue now?
     
  6. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    I'm guessing something worked loose in the jack, and its ground connection is intermittent. FLexing the connection a bit causes it to "make" and then you get sound.

    How's it installed? Is it actually mounted inside the bass, or in some other configuration? If anything external is visible, a pic might help sort things out.
     
  7. Muyy

    Muyy

    Sep 4, 2009
    Orlando, Fl
    its just mounted to the outside, the back of the pickup is adhesive. the pickup is vertical under my tailpiece, and the jack is just stuck to the back of the tailpiece with some double sided tape. nothing fancy.
     
  8. Muyy

    Muyy

    Sep 4, 2009
    Orlando, Fl
  9. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Of course I'm speculating about all of this, but at the same time, my experience with doing a fair amount of gear repair is that most problems turn out to be rooted in something mechanical. If you could sneak the jack off of there, maybe it has a cap that unscrews, and you could see if there is something broken or disconnected in there.

    Some of those cable mounted 1/4 inch jacks are just downright cheezy, and break easily. My favorite for this use is the Switchcraft jack, which can be gotten through Parts Express or Mouser. I'll look for a link to my magical output jack mounting method.
     

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