Odd hum problem - advice needed

Discussion in 'Pickups & Electronics [BG]' started by lordradish, Jul 19, 2022.

  1. lordradish

    lordradish Supporting Member

    Jul 20, 2006
    Vermont
    Hey, folks,

    I have a bass with a single Nordstrand Zen Blade and the OPB pickup. It is in a well-shielded cavity. Ever since I got the bass, I've noticed a sort of high-pitched hum (not like the typical grounding hum). It doesn't matter if my hands are touching the strings or not. The only time the hum goes away is if is sitting face down, either on the ground or on my lap.

    When playing, it varies in intensity, depending on which way I'm facing. Few things:

    • I've checked for bad solders, touching wires, all that, numerous times. Everything looks good. I didn't wire this bass, but I do understand wiring somewhat. It looks well-done. Nothing loose, everything's neat.
    • It does vary in intensity, depending on which way I'm facing, but only disappears if face down. It does this whether using an amp or a headphone amp. I've tried it with all of the lights off, I've tried it outside, so it doesn't seem to be dependent on some other interference.
    • When in passive, it's still there. Not as intense, but it's still there.

    I'm at my wit's end, here. I've been back and forth with the luthier proposing different things to try, and I still can't figure this out. Could it be a bad pickup or preamp?
     
  2. MidlifeBeginner

    MidlifeBeginner

    Jul 7, 2022
    If noise goes away facing down, the shielding in the back is good. Noise coming in the front is getting picked up. Top shielding may have an issue, or one of the pickups is picking up noise.

    When testing outside, leave your phone inside. Cell phones can be noisy.

    Does the noise go away if switched to just the Zen Blade?
     
  3. lordradish

    lordradish Supporting Member

    Jul 20, 2006
    Vermont
    Do you mean when I put it in passive? If so, yes.
     
  4. MidlifeBeginner

    MidlifeBeginner

    Jul 7, 2022
    The Zen Blade is a hum bucking pickup. Hum bucking is designed to cut 60Hz hum, but will cut noise over a wide frequency range.

    OPB pickup (I assume you mean original precision bass) is a single coil pickup. That can act like an antenna. If you really want that shape of pickup, but cut hum, Nordstrand makes a 51P4S. I have not heard what they sound like.

    Rolling tone off a little bit can cut high frequency buzz a lot. I have a bass with an unshielded control cavity that picks up noise from my computer. Until I get around to shielding it, I just back off tone a tiny bit.
     
  5. MidlifeBeginner

    MidlifeBeginner

    Jul 7, 2022
    Did you check the bridge grounding?
     
    scottm, wysiwyg248 and Mcabe like this.
  6. lordradish

    lordradish Supporting Member

    Jul 20, 2006
    Vermont
    I might have got the lettering wrong, by OBP I meant the nordstrand preamp. There's only one pickup, the Zen.

    I have to roll off the high end to the point of mud to make it not noticeable.
     
  7. lordradish

    lordradish Supporting Member

    Jul 20, 2006
    Vermont
    I will look, I'm hoping to not have to take that apart, as it's headless. But wouldn't it stop buzzing when I touch the strings, if that were the case?
     
    scottm likes this.
  8. Mcabe

    Mcabe

    Jan 7, 2020
    New Jersey
    I had a bass with hum that would not go away when I touched the strings. The ground wire from the bridge had snapped. Replaced it, and no more hum.

    Is there any noise that goes away when you touch the strings? How about if you touch the outside of the output jack?
     
    mikewalker likes this.
  9. micguy

    micguy

    May 17, 2011
    Is the pickup wired in series or parallel?
     
    Jefus likes this.

  10. It’s the opposite. The 60 cycle hum will stop when you touch the strings if the bridge ground is connected. That shunts all the noise your body picks up to ground instead of it interfering with the pickups. You don’t need to disassemble anything to check. Use a multimeter and see if there’s continuity from the metal on the bridge or the string ball ends to the sleeve terminal on the output jack or the metal cover of a plug plugged into the output jack.
     
    monsterthompson, BlueTalon and Mcabe like this.
  11. Mcabe

    Mcabe

    Jan 7, 2020
    New Jersey
    This sounds like RFI, which is another reason I would check the bridge ground.
     
    BlueTalon likes this.
  12. uOpt

    uOpt

    Jul 21, 2008
    Boston, MA, USA
    Does the noise get better when you touch the output plug (on the cable)?
     
    Mcabe likes this.
  13. mikewalker

    mikewalker Supporting Member

    Jul 30, 2017
    Canada, Eh!
    Do other basses do the same in the same place? if it cancels out the noise by changing the orientation, it's some nasty electromagnetic inteference. My last studio had a metal roof, and in the third floor suite, had a similar problem. There was a 25KV transmission line ten feet away from the roof! I started using a Lightwave (optical!) bass and a Line6 Variaxe up there because it was such a hassle having to sit at precisely the right angle and stay there the whole track... that building was the inspiration for my multiple-brand "humbucking jazz bass noise-resistance shootout test" (which I still havent gotten around to publishing)
     
    BlueTalon and lordradish like this.
  14. Just as a thought, how bad is it? Could a filter capacitor be added to the output cct to attenuate that freq? Can't offer much more as I've no experience designing ccts, I can build 'em and read 'em, but that's about it.
     
  15. Check bridge grounding, and also if your bass has a pickguard, the connection to cavity grounding.
    Last, but not least, check your pickups screws and springs and input jack, perhaps something is not making full contact with the cavity grounding when the bass is in playing position but contacts well when stored facing down.
     
    lordradish likes this.
  16. lordradish

    lordradish Supporting Member

    Jul 20, 2006
    Vermont
    I'd rather not have to mod it... it should just be done correctly. Thanks though.
     
  17. lordradish

    lordradish Supporting Member

    Jul 20, 2006
    Vermont
    Do I have to remove the bridge to check the ground? It's actually 6 individual ones (headless).
     
  18. lordradish

    lordradish Supporting Member

    Jul 20, 2006
    Vermont
    Nope, none of the other basses do it. I tried moving it next to an LED lamp as well as an outlet, and that didn't change anything.
     
  19. lordradish

    lordradish Supporting Member

    Jul 20, 2006
    Vermont
    I will definitely try this, thanks.
     
    monsterthompson likes this.
  20. uOpt

    uOpt

    Jul 21, 2008
    Boston, MA, USA
    No. You just have to see whether touching the output plug behaves differently than touching the strings.

    Or use an ohmmeter between plug and strings.
     
    DiabolusInMusic and Mcabe like this.