Shielding a MIM Jazz Bass Cavity

Discussion in 'Pickups & Electronics [BG]' started by selowitch, Feb 3, 2012.

  1. selowitch


    Aug 6, 2005
    Rockville MD
    I have a recent (2009-2010) MIM Jazz Bass whose body cavity is covered in the same paint as the surface of the body, including the clearcoat. I guess this is actually pretty typical. I think there is already a layer of conductive paint under the color coat; however, if I did choose to shield the cavity myself (either with copper tape or with paint), would it be beneficial to Dremel off the paint covering the cavity first? My reasoning is that neither the tape nor the paint would adhere to the wall and floor of the cavity very well with the clearcoat in place.

    Actually, even if I were to do something like this, I'd sooner do it to a cheap Rondo than to a Fender, but that's a separate question, really.

    I of course do not want to damage the surface finish at all.
  2. 96tbird

    96tbird PLEASE STAND BY Supporting Member

    Shielding tape has a fairly aggressive adhesive. Aggressive enough to hold on well to the shield paint in my bass. The smoother the surface the better the adhesion. Since clear coat is thicker than paint, it will likely present a better, smoother surface for adhesion; go for it.
    BTW why do you think it wouldn't stick to clear?
  3. selowitch


    Aug 6, 2005
    Rockville MD
    Same reason that one sands wood before priming; better adhesion to a rough surface.
  4. TNcaveman


    Feb 1, 2012
    I just got a used MIM Fretless Jazz (2002) and had noise problems. I found that the bridge ground is a joke - not even sure it was actually made contact under the bridge. I got some of the copper tape and lined the neck pickup cavity to the control cavity and the tape stuck without a problem. I also lined the bottom of the control plate w/ the copper tape to get better grounding to the pots. I used a new ground wire that was 18 ga copper to the bridge. Under the bridge, I placed a layer of tape. The new ground wire is spread out under the tape. All the ground wires were clipped from the pots and wired them with a star ground. The star ground is tied down with a brass screw and washer and connects to the shielding tape. Noise problems gone.

    BTW - my MIM jazz did not appear to have any shielding paint. If there is no ground wire tied to the wood via a screw which is through the conductive paint, then your's isn't shielded either.

    Good luck,

  5. selowitch


    Aug 6, 2005
    Rockville MD
    Mine appears to have grounding lugs on the cavity floor to which grounding wires are attached.
  6. 96tbird

    96tbird PLEASE STAND BY Supporting Member

    Huh? Sanding wood smooths wood; for a resulting smooth level finish. That's why one uses increasingly finer grit. Sealer soaks into the wood fibers, dries rapidly and seals it so it won't soak up the paint or varnish. One then sands to further smooth the finish.

    No, friend, a smoother finish offers better adhesion. Ever try to get tape off a window? Compare that to taking.tape off a piece of unfinished wood.

    Your ground wires in the cavities definatley point put that shield paint is under the finish. How good of a connection its making, if any is in doubt. The finish is preventing contact. I guess those Mexican workers don't get electrical theory.

    Now quit mucking about and shield it. ;)
  7. bassbenj


    Aug 11, 2009
    My 2002 had shielding paint and it "sort of" worked too. But in spite of the shielding there was still a bit of hum left that came and went when you touched the strings. So one day, I just bit the bullet and went after it all with copper foil, proper grounds etc.

    ALL residual hum totally gone! There really wasn't a whole lot of annoying hum there to begin with, but I SWEAR that bass sounds so much better now that it's dead quiet!

    I didn't bother to sand anything. Just gave the cavity a quick once over with a heavy file to knock the big chunks out (sort of looked like sawdust stuck to paint) and vacuumed all the dust out and then just stuck the copper on. Worked fine.
  8. None of you used conductive paint at all? I can just use copper tape, cover the pickup and control cavities, as well as a small surface area on the area where the bridge ground meets the bridge, and maybe around the neck pickup cavity on the pickguard?
  9. Nonsense. If you want it to stick, you want a surface with some tooth. Just like when you glue wood, you want to rough up the surface with a coarse grit sandpaper, NOT sand it smooth.

    However, with copper foil, it would be an absolute waste of time to even think about the surface you are sticking it to, because the adhesive is so aggressive. You can almost use it as fly trap paper.
  10. Personally, I wouldn't put copper tape on a pickup, unless you liked that tone. It affects the flow of eddy currents, darkening thing up a bit.
  11. Wow I didn't know copper tape affected the does it work like that?
  12. 96tbird

    96tbird PLEASE STAND BY Supporting Member

    Nonsense. Clearly you don't understand how flat film adhesives work. Since it's flat on the copper, any bridging because of laying it on an uneven surface equates to less adhesive contacting the substrate.

    Put I a strip on wood and one in glass and try to take them off then get back to me.

    The point i am making is that some routs have rough buy lays sticking up. Hitting them with paper lessens "bridging" air gaps therefore it sticks better.
  13. If I get noiseless pickups, will that solve anything? Even though they may be noiseless, I assume there will still be some hum because of the unshielded cavities
  14. RustyAxe


    Jul 8, 2008
    What are you trying to fix? If it ain't broke, I just leave it alone.
  15. fhm555

    fhm555 So FOS my eyes are brown Supporting Member

    Feb 16, 2011
    Every MIM J bass cavity(s) I've opened up was lousy with dross from buffing the body. All but one had conductive paint in the cavities that was covered by the finish and one just had the conductive paint in there with no finish over it. Some had the finish crudely broken up to give the ground screws better access to the conductive paint and some just had the ground screws run through the finish, but every single one had a crap ton of dried up buffing compound left in them. I've put copper tape in all of them and to start with I spent (literally) a couple days dicking with the leftover buffing compound before shielding. After that I just knock down the worst of the warty looking bumps and slap in the copper, and so far so good. The only reason I could see to spend a lot of time smoothing out things would be if you wanted your copper foil to look nice and smooth for photos. A rough substrate for it produces a rough looking copper foil application, but rough or smooth matters not to the final objective.

    I'm about to put a set of pups in my brothers old strat and I'm going to try shielding paint on it since it's got such a large area to cover.
  16. Do let us know how it goes!