Hum When I Touch Knobs?

Discussion in 'Pickups & Electronics [BG]' started by FunkMetalBass, Mar 1, 2010.


  1. FunkMetalBass

    FunkMetalBass

    Aug 5, 2005
    Phoenix, Arizona 85029
    Endorsing Artist: J.C. Basses
    I recently attempted a pretty complex wiring scheme this weekend, and I must have messed up somewhere because I get a horrible hum when I touch the knobs.

    The bass contains:

    Aguilar OBP-3
    EMG 45P, EMG 45TW (w/ coil tap switch)
    Modboard Tremolo
    Killswitch

    My thought is that the lack of bridge ground is causing the issue, but the EMG diagrams specifically say not to ground at the bridge because of internal grounding.

    Any ideas?
     
  2. grounding. though i had a similar problem but the hum could be stopped when i touch anything metal on the guitar. still should be an electrical issue
     
  3. FunkMetalBass

    FunkMetalBass

    Aug 5, 2005
    Phoenix, Arizona 85029
    Endorsing Artist: J.C. Basses
    I have to go through and re-check all of the wiring anyways. Maybe it'll miraculously fix itself.

    If anybody has any suggestions for where to look, please speak up.
     
  4. Gord_oh

    Gord_oh Midtown Guitars: Ulyate Pickups & StringJoy Supporting Member

    Oct 4, 2008
    Michigan
    check grounding to the bridge, between pots, (to the switch?)

    is it shielded?
     
  5. FunkMetalBass

    FunkMetalBass

    Aug 5, 2005
    Phoenix, Arizona 85029
    Endorsing Artist: J.C. Basses
    No grounded to bridge (according to EMG) because of the internal pickup grounding. Not sure if the Aguilar OBP-3 counters this or not, though.

    Do I need to have a ground wire running between the pots? If so...oops. That will be remedied soon.


    One of the switches is a killswitch, just a SPDT switch set up with ground | positive | negative.

    The other switch is another SPDT switch (grounded also) that is used as a power switch for the modboard unit, but that's all got quick-connect stuff controlling it, so I doubt there are any problems there.

    The third switch is a DPDT coil tap for the EMG 45TW. I'm 99% positive that I grounded it as shown in the diagram, but I'll have to check again.

    I don't have the cavity shielded yet (I may have to modify its size slightly), but that will be on the list. In any case, I seriously doubt that the shielding has anything to do with the extreme levels of hum that I'm hearing. It's almost drowning out the bass' signal.


    I'll let you guys know what happens when I go back through the wiring tomorrow.
     
  6. Gord_oh

    Gord_oh Midtown Guitars: Ulyate Pickups & StringJoy Supporting Member

    Oct 4, 2008
    Michigan
    shielding will make a world of difference.
    and yes you need to ground between the pots, at least thats what i was taught.
    which makes sense.

    does it do the same thing (like when you touch the knobs) if you touch the bridge?
     
  7. FunkMetalBass

    FunkMetalBass

    Aug 5, 2005
    Phoenix, Arizona 85029
    Endorsing Artist: J.C. Basses
    I know shielding helps, but I usually do shielding as a last step because, as I've said before, I still need to make a modification to the control cavity to accommodate.

    I'll ground between the pots. Note to self. I didn't see it on any of the wiring diagrams, so I was unsure.

    It doesn't change when I touch the bridge or strings, but it makes sense because I don't have a ground running to the bridge at all.
     
  8. Gord_oh

    Gord_oh Midtown Guitars: Ulyate Pickups & StringJoy Supporting Member

    Oct 4, 2008
    Michigan
    ok.
    i would ground between pots as a start.
    sounds like a ground issues being passed to the knobs.
    then ground (once and if you decide) to the cavity shielding.
     
  9. bassbenj

    bassbenj

    Aug 11, 2009
    All pots should be grounded! The fact that you get a loud hum when you touch the knobs shows they are not! The usual way to ground pots is when they are mounted on a metal plate that is grounded (as in a jazz bass) or as people have mentioned by running a ground wire from pot to pot soldered to the backs of the pots. Since the backs are crimped on the mounting shaft assembly that grounds them too (assuming they are standard pots and not plastic or something!) So try grounding the pots. If the signal then cuts out entirely, it means you've miswired a signal lead to the pot ground and recheck all wiring. If it works you are home free.

    Good luck.
     
  10. FunkMetalBass

    FunkMetalBass

    Aug 5, 2005
    Phoenix, Arizona 85029
    Endorsing Artist: J.C. Basses
    Thanks for the heads up.

    I'm sure I'll have to re-wire anyway because, in checking it again through an amp last night, I noticed that the stacked volume knobs didn't work (*sigh*).
     
  11. FunkMetalBass

    FunkMetalBass

    Aug 5, 2005
    Phoenix, Arizona 85029
    Endorsing Artist: J.C. Basses
    Well, I went through and grounded the pots & switches, re-checked all of the wiring, and it still hums and the volume knobs still wont work. Yet again, I'm giving up and taking my bass into the shop.

    I don't know why EMG pickups always give me such a hard time, but I can never get it right.

    Maybe I'll have the tech write down what he did so that I can learn from it for next time. He'll also make the wiring look 9000 times better than I could, so my control cavity will be nice and neat.

    Thanks for all of the help, guys.
     
  12. This thread possibly has the best name ever.
     
  13. FunkMetalBass

    FunkMetalBass

    Aug 5, 2005
    Phoenix, Arizona 85029
    Endorsing Artist: J.C. Basses
    :lol:

    You're the first person to notice.
     
  14. I Know! Do you?
     
  15. bill_banwell

    bill_banwell

    Oct 19, 2002
    England
    I'd hum if you touched my knob..
     
  16. FunkMetalBass

    FunkMetalBass

    Aug 5, 2005
    Phoenix, Arizona 85029
    Endorsing Artist: J.C. Basses
    giggity
     
  17. bunny10

    bunny10

    Mar 11, 2006
    I had the same problem today when I put a set of EMG's in my bass. I carefully went thru the wiring and found that I had reversed the white and black wires that went to the jack. Switched the wires and it was go to go.

    Hope this helps.
     
  18. Yok

    Yok

    Oct 14, 2011
    Sydney, AU
    I am having a similar problem.

    I had done a real bad job at chucking an active EMG MM pickup with simple volume/tone control into a bass and if I touch the volume knob, it goes BZZZ until I let it go, it works, everything works, but there is this BZZZ when I touch the volume knob!
     
  19. Primary

    Primary TB Assistant

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    Jun 14, 2021

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