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modding a yamaha bass to be passive

Discussion in 'Pickups & Electronics [BG]' started by narcopolo, Apr 20, 2010.


  1. narcopolo

    narcopolo

    Sep 12, 2005
    richmond, va
    hi guys!
    i got ahold of a yamaha rbx374 for very cheap - the bass has two MM style pickups (passive) and active EQ.
    here are the specs for a similar model: http://www.yamaha.com/yamahavgn/Documents/Guitars/RBX760A_E.pdf

    i'd like to rewire the bass to be passive - i have plenty of tone control from my sans amp and my bass head, and i just want the sound coming out of the bass to be as close to what the pickups sound like as possible.
    as far as controls go, the thing currently has four knobs - (active)treble, (active)bass, blend, and volume. all i want is a volume for the front pup and a volume for the back pup.

    my reasons are that it's not my primary or even secondary bass (so i'm not gonna be devastated if i make a mistake), i'd like to learn how to rewire basses, and i don't like the active tone.

    it seems like a fairly easy first project, but i'd love it if anyone has any insights as to how to proceed. like i said, this is a bass that i don't mind experimenting with.
    if anyone has any cool alternative suggestions, i'm open to that, too.
    thanks in advance!
     
  2. take out the electronics and then follow a wiring diagram for some other bass with 2 volumes and one tone
     
  3. narcopolo

    narcopolo

    Sep 12, 2005
    richmond, va
    a jazz bass, for example?
     
  4. EXACTLY…
    The humbuckers on a RBX374 have only two wires coming out, like the jazz pickups do…so a Jazz bass wiring diagram with two volumes + tone is one of the simplest schematics you can follow for your RBX.
     
  5. narcopolo

    narcopolo

    Sep 12, 2005
    richmond, va
    so i looked at the wires coming out of the pickup cavities, and while there are only two wires, one of those wires is much thicker and contains a separate strand within the insulation. I'm not sure if I'm describing this correctly:
    there is a thin, green, insulated wire coming out of each cavity. there is also a thicker, black, insulated wire coming out of each. inside each thick black insulated wire is a thin insulated wire and some uninsulated wire. they go to separate pots (you can see it in the pdf i posted).
    the presence of this third wire confuses me.
     
  6. narcopolo

    narcopolo

    Sep 12, 2005
    richmond, va
    specifically, i think one goes to balance and one to volume . . .
     
  7. JackANSI

    JackANSI

    Sep 12, 2006
    PA
    Its very hard to tell in the PDF, but it looks like the single green wire is to connect to the shield behind the pickups. If it is connected to ground, then thats where it should stay. otherwise the shielded wire (the one with the insulated wire inside the other) is for the pickup. The outer should probably go to ground and the inside will connect to the pot.

    I've never tried this with any Yamaha, but don't be surprised if there isn't a whole lot of volume coming out of the bass. Might not be an issue, but sometimes it can be when doing this.
     
  8. narcopolo

    narcopolo

    Sep 12, 2005
    richmond, va
    i've heard that the pickups are pretty hot on their own, and the bass is going into a sansamp before it goes to the amp. i'm hoping it'll be about as hot as my jazz.
     
  9. Pickups are plenty hot, as you’ve said…I don’t think you’ll have a problem with volume…besides, the sansamp can get plenty loud, anyway…

    Wiring…
    The thick black cable is from the pickup…the bare core connects to ground, the insulated core is your signal.

    Thin green wire sounds like it’s a shield ground…connect this to the ground…
     
  10. JackANSI

    JackANSI

    Sep 12, 2006
    PA
    Good to know they are going to be hot enough. Forgot to tell you good luck!
     
  11. narcopolo

    narcopolo

    Sep 12, 2005
    richmond, va
    thanks! i've got two basses in front of it, so even if it gives me trouble i'm not in hot water . . .
     
  12. narcopolo

    narcopolo

    Sep 12, 2005
    richmond, va
    dunno if anyone's interested, but i did the mod, using a basspartsexpress vintage jazz wiring kit. the existing holes for the pots were too narrow, so i had to sand them out. the hole for the input jack was too deep for a fender style jack, and the old jack was suspect. fortunately for me, the bass originally had four knobs and a jazz obviously has three. so now the jack is up front. this worked out well, because now i don't have a weird hole on the front (just a weird hole on the side).
    i put a string on there and smacked it a few times. all the pots are doing what i wired them to do, which is a good sign. once i've strung it for real and set it up, i'll lay down something to show the new tone. i'll post some pics too, just to show how much nicer it looks with a front jack.

    anyway, thanks to everyone who weighed in. i love rewiring and personalizing gear!!!!
     
  13. narcopolo

    narcopolo

    Sep 12, 2005
    richmond, va
    fyi - the new pots are 250k whereas the old ones were 850k. the wiring kit also came with an orange drop capacitor. i've ordered one for each of my other basses.
     
  14. Bardley

    Bardley

    Nov 16, 2007
    Louisville, KY
    Congrats! I recently did the same thing to my Warrior 5 and I couldn't be happier with it.
     

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