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Shield question

Discussion in 'Pickups & Electronics [BG]' started by FeuerFrei, Apr 10, 2009.


  1. So I'm shielding a bass (and replacing a dead soap bar pickup) I was told that I didn't need to shield the pickup cavity on soapbar pickups as they're already shielded, so just the electronics compartment is all I need.

    Thoughts on this one?
     
  2. chicago_mike

    chicago_mike

    Oct 9, 2007
    Chicago - LA - Rome
    Endorsing Artist : Genz Benz
    ou could get away with shielding the bottom of the route. But the walls should be covered too.

    Good trick : Solder Wick makes excellent ground wire. Save the used stuff.
     
  3. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    I only shield control cavities on basses with hum canceling pickups. The cavity has unshielded wires in it. The pickups should be fine without shielding in the pickup rout. Wouldn't hurt though.
     
  4. kraigo

    kraigo

    Jun 21, 2007
    Minneapolis, MN
    I'm guessing it depends on the pickups. Maybe David can talk about his own. I'm assuming the Nordstrands are shielded inside. Both David's own (SGD Luthierie) and Nordstrands have shielding cables among the wires, so I guess that they're shielded internally.

    As long as you aren't introducing ground loops, a little extra shielding won't hurt. I'm not going to pop the shells off of either my SGD pickup or my Nordstrands - they're potted in epoxy and I'm not going to take the chance of breaking something.

    KO
     
  5. Alright, thanks for the update, I'm waiting for an email back from Copley Guitars tech person about what kind of pickups they put in their basses, as I tested the two soap bars, one of them will show resistance, the other one has nothing doing, so I'm having to assume since it was so quiet on the output, that it's dead, and while I got it torn apart, I wanted to know.

    Thanks again, I think I'll just shield the control cavity for now, and once it's back up and running, If needed, I'll tear it apart.

    This is my first time tearing a bass down and putting it back together, keep your fingers crossed for me.
     
  6. Why would you want to only shield part of the bass when you could just as easily do all of it?

    The shielding in the pickup cavities may not be of any use depending on the pickups, and some people argue that shielding doesn't do squat to begin with, but the way i see it, shielding is easy and inexpensive enough that you can just do it anyways and forget about it.

    I have both of my Jazz basses setup with only a bridge pickup.
    Even though i don't have anything in the neck pickup routes, i shielded them anyways just because i could. If i ever do put in a pickup, i am all set with shielding and i never need to worry about it.
     
  7. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    Yes, my pickups are internally shielded, and the metal parts (magnets and blades) are all grounded. I actually enclose the entire pickup in a brass mesh faraday cage.

    Ground loops are not really possible in an instrument, since there is only one ground connection to your amp. I think it's mostly a myth, and any change in ground potential from one wire to another in a bass would be so small as to not amount to much of anything.

    Ground loops occur in AC powered gear when you have two pieces of grounded gear attached together via patch cords.

    Yeah, you can't remove the covers on my pickups without destroying them. But as I said they are fully shielded and use shielded 4 conductor cable coming out.
     
  8. walterw

    walterw Supportive Fender Gold Supporting Member Commercial User

    Feb 20, 2009
    alpha-music.com
    really? tell us more! does this cage act differently than just say, solid copper foil shielding? would lining single-coil pickup covers with a grounded mesh serve to reduce hum without the tonal loss that solid shielding supposedly causes?


    thank you! people obsess about "star grounding" their guitars, and other such mis-applied amplifier design ideas.
     
  9. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    I use thin brass screening for shielding. The thicker the shield the better it works, but then you are more susceptible to eddy currents which cause high frequency loss. So the screen works better than foil, but isn't like a thicker sheet of brass or copper, like a pickup cover (which is usually nickel silver, a form of white brass).

    Shielding pickups only causes a tonal problem if you wrap foil around the coil and let both ends of the foil touch. This causes a closed conductive loop around the coil, and that will change the tone of the pickup somewhat, usually by rolling off some high end and flattening the resonant peak.

    You can wrap foil around the coil if you don't let the two ends touch.

    Right. It's important in amplifiers, especially tube amps with high voltages. But it's pretty useless in basses and guitars, and I've read more posts with people saying it caused hum than it eliminated!

    If star grounding was so important all the big names would be using it.

    Nice solid paths to ground and neat wiring is the best thing.
     
  10. slyjoe

    slyjoe Supporting Member

    Jun 28, 2008
    Valley of the Sun (AZ)
    Not mostly, 100%. I hear this a lot. The only way to get a ground loop is to have two pieces of gear with different grounds (to the earth). Doesn't happen in an instrument.

    Correct, AND they have different ground potentials; see above.
     
  11. SGD Lutherie

    SGD Lutherie Banned Commercial User

    Aug 21, 2008
    Bloomfield, NJ
    Owner, SGD Music Products
    I originally wrote it's NOT possible, then I thought I'd give it the benefit of the doubt... but I've been saying for years that it just can't happen. ;)

    I still stand by that.

    Exactly. You can't have two ground potentials in an instrument since there is only one ground. Which is at the amp's input.
     
  12. And we're done with the first part


    http://www.evercrack.net/temp/caged.jpg


    Now waiting to hear back from Copley's tech, who apparently is on a two week vacation (useful for when you need assistance)
     

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