1. Please take 30 seconds to register your free account to remove most ads, post topics, make friends, earn reward points at our store, and more!  

Wiring problem

Discussion in 'Pickups & Electronics [BG]' started by Yigal83, Dec 26, 2016.


Tags:
  1. Yigal83

    Yigal83

    Apr 16, 2016
    IMG_20161226_133735. IMG_20161226_133706. Hi guys, i recently recieved a peavey rbx270j in a trade. It's a pj bass. The bass hums unless i touch the strings and the j pickup has no volume. Here are pics from the wiring, would appriciate any help from you all. I imagine there is a grounding problem aswell.
     
  2. Growlmonkee

    Growlmonkee

    Jan 30, 2013
    Florida, U.S.
    JazzBass_Standard. The middle pot appears ungrounded, (the metal casing should have a ground wire soldered to it), Can't tell for sure, it looks like only one pickup is wired to the tone pot, then jack. This is Seymour Duncan's Jazz Bass wiring diagram, they are a good source for wiring. a P/J bass wired vol/vol/tone is the same as this. of course in your bass one of the pickups has yellow = the white wire on the diagram pickups, and the bare braided shield for that pickup's black wire, (which works fine). there is no pic of the how that yellow wire is soldered to the pickup itself, "yellow" is different than most pickups, but, may be fine, if it's soldered to the pickup correctly
     
    Last edited: Dec 26, 2016
    PortlandBass77 and Yigal83 like this.
  3. NigelD

    NigelD Supporting Member

    Aug 14, 2013
    Looks like a vol/ blend/ tone circuit.( wire pups to blend pot, blend out to vol, vol out to tone, tone to output jack) , Diagrams posted in pups/electronics.
     
    Growlmonkee likes this.
  4. Yigal83

    Yigal83

    Apr 16, 2016
    I'm almost sure it is a v/v/t circuit. Unless it was moded.
     
  5. Growlmonkee

    Growlmonkee

    Jan 30, 2013
    Florida, U.S.
    A blend pot is a "double" pot, I couldn't tell, but Nigel is probably correct, if that middle pot has 2 sets of terminals. TB member Walter W made a wiring diagram, the blend pot isn't grounded, it sounds really good, ( I kept a copy), if you have to rewire , the ground wire from the bridge isn't shown, but, it's clear, and well drawn. If your blend pot is grounded, there would be another ground wire diagonal across the 2 blend pot terminals with no wires in this diagram, (that wire goes to ground.) jazz%20bass%20ungrounded%20blend.
     
  6. Growlmonkee

    Growlmonkee

    Jan 30, 2013
    Florida, U.S.
    I used Walter's diagram on my Jazz bass, sounds great without the blend grounded, If it's V/B/T the middle pot isn't a vol. pot, that might be the problem you're getting (it might all be working, as you would not have volume with the one volume pot turned down
     
    Last edited: Dec 26, 2016
  7. Yigal83

    Yigal83

    Apr 16, 2016
    The specs say it is indeed v/v/t, and prior owner did not mid it. Thank for your input guys.
     
  8. That's clearly a blend pot. It has an "MN250k" sticker on it. MN is the taper of a blend pot. A volume pot would have an A, B, or C taper.

    When in doubt, look at the terminals. If you have 6, then it is a blend pot. A volume or tone pot has only 3.
     
    DrummerwStrings, 40Hz and Yigal83 like this.
  9. 40Hz

    40Hz Supporting Member

    Definitely modded. An Alpha MN250K is a dual-blend pot.

    Oops! I see @line6man got it in ahead of me. :thumbsup:
     
    Last edited: Dec 26, 2016
    Yigal83 likes this.
  10. Yigal83

    Yigal83

    Apr 16, 2016
    yep, turnes out to be a blend pot. thank alot guys. do you see where the grounding promlem is?
     
  11. NigelD

    NigelD Supporting Member

    Aug 14, 2013
    Loosen your bridge and make sure the ground wire is making contact to it.
     
    bassmeknik and Spidey2112 like this.
  12. Isnt that a Yamaha, not a Peavey?
     
  13. You said the hum goes away when you touch the strings? That would seem to indicate the bridge is making good contact with the ground wire.
     
    Jazz Ad and NigelD like this.
  14. this is a blend pot mod gone wrong. even from that tangle, I can see at least two wires going to the wrong place. plus the frayed shield from the bridge pickup is pretty dodgy.

    you need to remove the blend pot and reinstall it.

    please don't take this the wrong way, but tbh, when hack jobs like this grace my bench, I start from scratch with new pots. when someone had been using bad soldering technique, the reliability of pots especially is really compromised. and desoldering and resoldering just makes this worse.
     
    Will_White, Yigal83 and Spidey2112 like this.
  15. Deltatim

    Deltatim

    Nov 5, 2016
    Stockton, CA
    +1/\
     
  16. Spidey2112

    Spidey2112

    Aug 3, 2016
    I can see the ground for the bridge coming out of the body, but can't clearly see where it connects...
     
  17. Spidey2112

    Spidey2112

    Aug 3, 2016
    ??? Andy, if a common cause of hum is a bad ground from the bridge, then how does touching the strings, thereby removing the hum, indicate good contact from this part of the circuit... seems like you're creating a parallel circuit, shunting the bridge ground, whether it's good, or not... a simple measurement from bridge to wherever that connects inside the control cavity (I mentioned I can't see this, from the pics provided) would rule out whether it's good, or not...
     
  18. What I meant was that in a normally wired bass, the reason the hum gets quieter when you touch the strings (assuming metal strings that aren't coated or tapewound) is that the metal string touches the metal bridge which touches the bridge ground wire. Your body is touching the ground of the instrument cable/amp by way of going thru the strings and bridge to get to ground. If the bridge didn't have any contact to ground, touching the strings wouldn't quiet the hum.

    sure, it wouldn't hurt to check - but not sure what the OP's skills are and thought removing the bridge might be chasing the wrong demon at this point in time. And just measuring with an Ohm Meter from bridge to output jack is a lot easier than pulling the bridge off anyway.

    With well shielded cavities, humbucking pickups (I think the OP has a single coil bridge pickup) and good wiring, you really don't need that bridge ground strap (and EMG tells you to remove it because their pickups are shielded). But most of us use our bodies touching strings to ground out the noise.
     
  19. Spidey2112

    Spidey2112

    Aug 3, 2016
    Thanks, Andy!
     
  20. You are welcome.

    BTW .. this is a bit silly sounding .. I have an ABG that hums unless I touch the output jack ground. But it has a wooden bridge with bone saddle and besides that it has tapewound strings. So even if I did ground the bridge/saddles the tapewound strings would defeat me. So when I record and need it quiet, I take a second 1/4 guitar cable from some unused (but grounded) jack on the amp and tuck the other end of the cable into my sock :) that does the same thing that touching strings does on a normal bass and quiets the hum.
     
    aguacollas and rufus.K like this.

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.