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Thread: Jazz Bass hums after pickup replacement

  1. #1
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    Default Jazz Bass hums after pickup replacement

    Hello, I wired my guitars and some guitars and basses of my friends in this last year, so I got a bit of experience, but now I have a big unsolvable problem with a bass of a friend of mine.
    It's a good model of a Fender Jazz Bass Mexico. My friend wanted replace the original pickup with a set of Seymour Duncan Quarter Pound.
    This is the original layout from the Fender datasheet:



    I just wired the new pickups exactly how the old pairs were: the two black wires on the own volume pot and the hot wires on the own central lug's volume pot. At home everything worked ok, and included me none of my three friends had notice hum. But after some days at high volume my friends noticed a sort ground noise, it disappear when you touch strings, bridge, etc... With both volume pots and tone at max the hums is pretty noticeble.
    The new pickups are hum cancelling when used together.
    The ground wire is connected, indeed I didn't touch it. The metal plate allows (I verified it) the connection to the ground of the three pots and the sleeve of the jack. I really can't imagine what's wrong, but there's something.

    I really need help, please!

    Thanks!

  2. #2
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    Default Re: Jazz Bass hums after pickup replacement

    You need a ground wire from the input jack to the tone pot and then the volume pot. You did run one to the bridge didn’t you?


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    Default Re: Jazz Bass hums after pickup replacement

    Thank you,

    I didn't touch anything but the pickup wires. I took off the old ones and soldered the newer.
    The ground wire from the bridge was soldered on the tone pot with the cap. RIght in the diagram.
    There's no wire from the sleeve of the jack, and the tone pot and the volume pots because the metal plate make the connection between those parts. Indeed, strings, hardware, pots and sleeve of the jack (all this grounded parts) are connected together. Ground noise go away if I touch the grounded parts, else is loud enough to be annoying and not normal.

  4. #4
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    Default Re: Jazz Bass hums after pickup replacement

    I promise if you wire it like I said, it will stop humming.


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  5. #5
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    Default Re: Jazz Bass hums after pickup replacement

    Original layout doesn't have that extra wires, and it worked.
    I'm not so sure as you are, but I'm going to try when I will have back the bass.

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    Default Re: Jazz Bass hums after pickup replacement

    I still don't have the bass with me, but this bass gave a shock to my friend. How it could be possible?

  7. #7
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    Default Re: Jazz Bass hums after pickup replacement

    Bad wiring in a building can absolutely give a bad shock. Incorrect mains grounding. This isn't an instrument problem, it is a building code issue.
    Dave, Ambassador/Writer/Artist for Seymour Duncan

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  8. #8
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    Default Re: Jazz Bass hums after pickup replacement

    As I thought, indeed.
    Anyway, there's something wrong in the wiring bass, even if I can't explain it, since I just replace the old pickup with the new pickup resoldering in the same way. The black wires on the pots, the hot wires (red and white) on its volume pots's lug. And I didn't touch the ground wire from the bridge.
    I say it again, it doesn't have the wires that connect the pots to the sleeve of the output jack because the metal plate makes the connections.

    Does someone have further idea?
    Last edited by Ichabod; 09-12-2019 at 02:35 AM.

  9. #9
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    Default Re: Jazz Bass hums after pickup replacement

    https://docs.google.com/gview?embedd...s_Standard.pdf

    this is what it should look like. do you have a multimeter? if you touch a ground and the hum goes away, there is a grounding issue some where. as far as the shock, that sounds like a mains issue like dave said. there should never be that kind of current running through an instrument cable

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    Default Re: Jazz Bass hums after pickup replacement

    When I'll have back the bass from my friend I'm going to add those pieces of cable to join the sleeve of the jack and the three pots, but what I can't understand is that using a multimeter those parts are already connected even if there's no wires because the metal plate. Just like it was with the old pickups nad it worked without those cables. It's a really tricky issue!

  11. #11
    LoveMachineologist jeremy's Avatar
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    Default Re: Jazz Bass hums after pickup replacement

    the metal plate should work fine but obviously something isnt grounded. is it actually a plate or just a film/tape on the pickguard? the fact that it worked fine at your place means maybe something came loose or there is a cold solder joint or ??? luckily you dont need to pull the strings off to check the wiring on a jazz bass

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    Default Re: Jazz Bass hums after pickup replacement

    It's really a mistery! I can't check the bass, now. But I checked it, and the ground were where it supposed to be. The bass played, volume pots worked both, so the tone pot.

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    Default Re: Jazz Bass hums after pickup replacement

    Hi, I got the bass. Now I have to fix this awful issue!
    The ground: Hardware (strings, bridge, metal plate...), black wires of both pickups (I checked, the black wire is soldered to a copper foil under the pickup, so that's to be the ground), one side of the cap, lugs 1 of both the Volume, Sleeve of the jack. All these things are in contact.

    What else?
    It's totally absurd!

    Is the orientation of the pickup important? One of the pickup is reverse wound, but this doesn't mean that I have to reverse ground and hot wires of one pickup, right?
    Everything is fine, indeed, I just desoldered the old pickup and soldered in the same place the new pickups.

  14. #14
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    Default Re: Jazz Bass hums after pickup replacement

    No, the orientation of the pickup shouldn't cause it to hum that much. If it is really bad, either the wires for the jack are reversed, or there is a cold solder joint on one of the ground wires. The plate should ground the pots without needing additional wires, but you can always test this.
    Dave, Ambassador/Writer/Artist for Seymour Duncan

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    Default Re: Jazz Bass hums after pickup replacement

    I tried to attach some clips from the sleeve of the jack to the pots. Just one wire on the jack, on the tip. I'm sure, I replaced even the jack with a new one. The sleeve is unsoldered, because the plate.
    A cold solder? It could be, but anyway the pickup results in contacts with the bridge (not the pickup, right the bridge of the bass), so with the ground.

  16. #16
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    Default Re: Jazz Bass hums after pickup replacement

    I worked on the bass right now.
    I desoldered all the pickups wires and I used the clips to attached the red and the white wires (the two hot wires) directly on the tip of the jack connector, and the black wires from the pickups attached together to the plate. I desoldered even the the ground from the bridge and attached it to the plate. In this way all the ground are connected together and I bypassed the pots. The pickup are directly connected to the jack. The bass sounds, as early, but the hum is still there.
    No changes and there's nothing else to try!

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