JMJ Mustang shielding question

Discussion in 'Hardware, Setup & Repair [BG]' started by OaklandA, Jun 20, 2019.

  1. OaklandA


    May 19, 2019
    So my JMJ has a pretty noticeable shielding issue. Especially in my office which has a lot of noises sources - computer, screen, lamps. ceiling fan, etc. Goes away when I touch the strings.

    So I have opened it up and am in the process of shielding. First I was a little surprised to see no attempts at shielding whatsoever. Not even some foil on the back of the pickguard.

    But I also see there is no wire running from under the tailpiece to a ground in the control cavity. In the past this has usually been the case. My question is, should I add a wire? Or will it be fine without it...just shielding the control & pickup cavities and applying foil to the back of the guard.

    Thanks in advance.
  2. KenB


    Jul 15, 2008
    Yellow Springs, OH
    There should be a wire under the tailpiece. Mine has one.

    But, if touching the strings changes the noise the strings must be grounded.

    Are you sure there is no wire coming into the control cavity from the tailpiece? Is there a hole drilled for the wire?
  3. OaklandA


    May 19, 2019
    Ah, on second look there is a wire coming from the side of the cavity which I'm sure is running from the tailpiece. oops. Pretty much renders this thread useless, lol. I'll continue on with the shielding process and see what happens.

  4. Axstar

    Axstar Inactive

    Jul 8, 2016
    That ground wire between the bridge and the ground side of the circuit acts as a pathway for all the interference your body picks up. On a well shielded instrument it isn't necessary. If you hear more noise when you take your hands off the bass then you need shielding, as you say above.

    Granted, the Starfire in my avatar can't be shielded easily, so I used coax cable and hoped for the best.

    I'm running nylon tapewounds on a fully shielded P bass, and experiencing no noise issues even though I've broken the ground path between my hands and the ground side of the circuit in the bass.

    If you fully shield the instrument then the wire isn't that necessary (my P bass with the tape doesn't need one).

    I had a Japanese Mustang for a while, and it didn't have any shielding either. It needed the control cavity and pickup route shielded, as well as the back of the pickguard. Once this was done the bass was whisper quiet. In such cases a 'bit of shielding' doesn't really do much; you need it to be as complete as possible, with full connectivity between ever bit of the shielding.
  5. OaklandA


    May 19, 2019
    A quick follow up. I completed the shield job - three coats of conductive paint plus a foil backing on the pickguard and it's now quiet as can be. The new strings sound great too (LaBella 760F MUS).
    mikecd1, WhoIsJOB and Axstar like this.
  6. mikecd1

    mikecd1 Supporting Member

    Mar 3, 2009
    New England
    I had the same problem and switched out the Jin Sung pots for CTS, shielded both cavities and then ran an additional ground wire from the back of the volume pot to the control cavity exactly like my USA Pbass has. Totally quiet.