Grounding Issue or Shielding Issue?

Discussion in 'Pickups & Electronics [BG]' started by Modern Growl, May 4, 2012.


  1. I've had 2 brand new instrument come in with the classic symptoms of grounding issues. Hum when not touching the strings (or anything metal on the bass, i.e bridge, etc...) And a static pop when playing if I take my fingers off the strings for a brief moment.

    Bass 1 - Stingray Classic (active, brand new)
    Bass 2 - Fender Jazz Custom Shop 64' Relic (all passive, brand new)

    All of my other instruments do not have these issues.

    The two things both of the above instuments have in common is poor shielding. The SR Classic has zero shielding that I can see, and the Jazz has that metal plate on the bottom of the control cavity.

    The ovbious: I checked all solder joints and everything is solid. I removed the bridge and looked at the ground connection there - solid.

    Whats the deal? Is the poor shielding causing this?
    FWIW - my apartment has pretty old electrical work and I'm not sure if there is a "true" ground though the outlets are 3 prong. But what is most perplexing is none of my instrumens - Sadowsky's, Alleva Coppolo or my other passive Fender Jazz have any of these issues :confused:
     
  2. jmac

    jmac

    May 23, 2007
    Horsham, Pa
    For me hum was always the result of poor shielding. YMMV.

    Take the basses to a qualified tech. I had hum on my 1979 MusicMan Sabre. I took the bass to a local luthier. He fixed it right up.

    I see that you're in NJ. I'm not sure how far this would be from you, but his name is Audric Jankauskas. He also happens to a terrific jazz guitarist.

    He works out of Pro Line Music; which is located in Fairless Hills, Pa (over the bridge from Trenton).

    He's worth the drive.
     
  3. +1000 for Audric Jankauskas!
    His work is amazing
     
  4. Both instruments are under warranty, so I wont be paying out of pocket for services.

    I'm more than willing to do the work myself as I have plenty of shielding tape & solder/etc... just trying to get a feel for what the issue is???
     
  5. Growly Lytes

    Growly Lytes

    Dec 4, 2009
    Downunder Oz
    Bass player
    One of my basses does this but ive gotten used to it over time.
    It can be done fixed with copper shielding.
     
  6. lscs

    lscs

    Dec 26, 2011
    Might, possible, maybe be oxidation/tarnish/gunk on the output jacks? Even if new. Just a guess.
     
  7. bassbenj

    bassbenj

    Aug 11, 2009
    While people talk about about hum from "grounding issues" generally that is not the case unless hum is HUGE. A broken ground wire will cause hum but usually it will be very loud and make the bass unplayable.

    The usual thing is shielding problems. Fenders especially seem prone to this as they use conductive paint which on occasion seems not to work right. (Usually it does work right and if not, it can be fixed with another layer or two). Copper foil always works.

    People talk about using a "star" ground in the bass and yes, this is best, but usually it's irrelevant for a bass and really only matters in super-high gain electronics like Mic preamps.

    If hum does NOT go away when you touch ground (especially when only one pickup is on) then that means single coil hum which is common for Jazz basses with single coil pickups. It can't be fixed by shielding.

    But if you open up the cavity and don't see copper foil or conductive paint (say the paint in the cavity looks suspiciously like plain old flat black rather than shield paint) then a copper foil shield job is probably in order. And be sure to shield at least the bottoms of pickup cavities too.

    If you see shielding in there, they it may be that copper foil pieces are not properly grounded (solder them together and run ground wire to Jack barrel) or conductive paint is not properly grounded. That is usually grounded with a wire again from the jack body to a wood screw with a lock washer that "bites" into the paint. Note that any unshielded areas (under pickups, wires to pickups, battery cavity) are potential hum sources if left unshielded. And even the best shielding if left ungrounded will not block hum!

    Good luck.
     
  8. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

     
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