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Pickup shielding with no body

Discussion in 'Pickups & Electronics [BG]' started by Alib8, May 8, 2015.


  1. Alib8

    Alib8

    Aug 16, 2014
    Poland
    Hi everyone, I wasn't sure if I should post this on the double bass side but I figure people would be more familiar with split precision pickups here.

    I mounted a split precision bass pickup on the bridge of my double bass, like so:
    p.


    I soldered it directly to a female input. Tone is nice, but there is a lot of ground noise, rolling of anything higher than 600 Hz on a graphic eq (-15db) plus turning the treble knob to 0 on the amp cuts of most of the noise, but at high volumes on stage it is still distractingly present, more audible than the guitarist's telecaster with the overdrive pedal switched on. Rolling off all the treble and high mids also makes the tone very muddy.

    Is there anything I can do to reduce the ground noise to a bearable level? Also could it be possible that I positioned the pickups wrong, or is it all the same with precision pickups?

    Thanks.
     
  2. LoveThatBass

    LoveThatBass

    Jun 28, 2004
    If your strings are not grounded to the output jack ground they are like an antenna for noise. This is accomplished by grounding the bridge the strings are connected to on a regular electric bass. I do not know anything about a double bass. If your stings connect to a metallic tail piece you can ground the tailpiece but if it is not you would have to devise a method to ground the strings
     
  3. Growlmonkee

    Growlmonkee

    Jan 30, 2013
    Florida, U.S.
    It's not the position of the pickups, the noise probably won't change at all by moving them. with the entire system in the open like it is, it's like an antenna, not just the pickups, but all the wiring too. You might do better with even a low cost Schatten upright bass pickup, it would sound better too.
     
    Last edited: May 9, 2015
  4. SamanthaCay

    SamanthaCay Like bass guitar OMG!

    Nov 16, 2008
    Denver, CO.
    Ground to the strings as mentioned.
    Also you can remove the pickup covers shield and ground them and last get them closer to the strings if you can, 1/8 is generally a good place to start.
     
  5. Can you wrap copper tape around the strings? That would be the easiest way to ground, provided you don't mind the unsightliness.
     
  6. Alib8

    Alib8

    Aug 16, 2014
    Poland
    Thanks for the suggestions, I grounded the strings with a bare copper wire touching each string and then tying the end of the wire to the inner metal sleeve of the output jack (or should i solder them to the ground lug of the jack?). The ground noise is lessened this way, I can definitely hear the difference, but I fear it is still not low enough.

    The plastic covers of the pickups are glued on tight so I can't take them off, but would wrapping the back and the sides of the pickups with copper tape help? Copper tape the pickup wires and output jack as well?
     
  7. Antisyzygy

    Antisyzygy

    Dec 8, 2014
    Washington
    I think you might benefit from using some shielded wire going from the pickup to the output jack? If I take any wire out of the shielding in my P bass the bass will instantly get noisy.

    You can find it much cheaper than this, but it's for reference : Allparts 25 Feet of Shielded Cloth Pick Up Wire for Gibson Les Paul Guitars | eBay

    When I shield basses I don't bother shielding the pickup covers, so the pickup tops are bare to the outside effectively. I don't notice any noise even though I leave that step out, even when I'm not touching the strings. The metal bridge of an electric bass is connected to the common ground and the metal strings touch the bridge, so when you touch the strings you are part of the ground.

    However, when I shield a bass, the pickups still have shielding surrounding them on all sides since I put it on the bottom side of the pick guard and in the cavity itself. Maybe it's worth a shot shielding the bottom and sides of the pickups with like a layer of insulator between the shielding and pickup (plastic wrap or something). Shielding the wire to the output jack is still necessary if you do that.

    Your shielding has to connect to the common ground, which sounds like that is your strings right now. That can just be a wire connecting the shielding to the current ground you have wherever is most convenient as long as it's connecting ultimately to the common ground.
     
    Last edited: May 9, 2015
  8. Alib8

    Alib8

    Aug 16, 2014
    Poland
    Thanks for the idea, I will buy copper tape and try taping the backs and sides of the pickups (perhaps the fronts too?); but does copper tape do any shielding by just being there (like the shielded wire, as a Faraday cage) or is it only effective if I run a wire from the surface of the copper tape to the strings/ground?
     
  9. Antisyzygy

    Antisyzygy

    Dec 8, 2014
    Washington
    I think in this application it will have to be connected to the circuit's ground if you want it to work properly. I'm not an electrical engineer though so I could be wrong, just took a few courses on that stuff in college several years ago. I started out as an EE major then switched to something else.

    I believe when electromagnetic radiation outside the shield induces a voltage on the shield, this may not be constant relative to the internal circuit if it's not connected to the common ground. The capacitance effect between the shield and electronics inside it can cause some noise in that instance.

    Again, take that with a grain of salt. I'm remembering some stuff I haven't used or even thought about in awhile. However the rule of thumb for shielding electric instruments is connect the shield to the common ground.

    You might try wrapping copper tape around the bottom and sides of the pickup, and then connect it to copper wrapping around the cables leading to the output jack. Connect the copper foil on the outside of the pickup wire to the common ground, whatever that is (probably your strings). The ground wire from the pickup itself needs to connect to the shield somewhere along the way too

    You might be able to wedge the pickup cable that is wrapped in copper foil under the strings, so the strings are touching the copper, and then the shield itself becomes your ground connection to the strings. You'll need to connect a wire from the ground on the output jack to the shield as well. When you touch the strings you should notice any noise goes away if it's grounded properly in that way, but best case is you won't have much noise at all even when you aren't touching the strings because of the shielding.
     
    Last edited: May 10, 2015

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