Discussion in 'Luthier's Corner' started by mahrous, Oct 11, 2005.

  1. mahrous


    Aug 13, 2005
    i am wiring my first bass at the moment.

    i have actually wired it already but the knobs dont do anything. i turn them down and the bass' volume is still as high as possible!

    i borrowed 3 knobs from my Aguilar preamp (for practice on this bass) 25k log pots. this is a P/J Jazz bass using Seymour Duncan Basslines QuaterPound P pups and SJB-3 in the bridge.

    Duncan says i should use 250k pots but i dont have them and i live in Egypt. still need to order them on the internet (any good shops besides allparts, stew-mac, guitarelectronics). i used Duncan's diagram to wire. 2 volumes and 1 tone.

    so what are the famous mistakes in electrickery that i might be doing?
  2. Rodent

    Rodent Supporting Member Commercial User

    Dec 20, 2004
    Upper Left Corner (Seattle)
    Player-Builder-Founder: Regenerate Guitar Works
    One of our TB sponsors - BestBassGear - is an excellent resource for your parts. Brian's site is http://www.bestbassgear.com

    You can also shop with confidence at Blueberryhill Bass. Jay's site is http://www.blueberryhillbass.com

    I'll leave the details of electrical troubleshooting to our more educated members. You may want to pose this question over in the pick-ups section if you don't receive an answer here.

    All the best,

  3. You answered your own question - You used 25k pots instead of 250k pots. In essence, you sent a boy to do a mans job. I think I can explain this correctly - a volume pot (potentiometer) is a resistor that is variable. It either allows a full voltage signal to go through at full volume or it pares it down to nothing when it's totally turned off. Your 25k pot only has the ability to introduce 25k of resistance to the circuit when you needed 250. That means that you don't have enough resistance to turn down the volume. The 25k pots are usually used in active circuits and the larger 250 and 500k versions are usually found in passive setups.
  4. Tim__x


    Aug 13, 2002
    Alberta, Canada
    They're miswired, any value of pot will work as a volume control (though low values will cause treble roll-off and an overall level reduction).
  5. mahrous


    Aug 13, 2005
    i believe they are mis-wired. actually i believe its a grounding problem. but i cant put my finger on it.

    without the tone knob, i could turn down the volume to off. when i added the tone knob it doesnt let me do that unless the tone is turned down to zero. if its turned up, i get that hum. before u jump to a conclusion, i grounded the tone knob but my grounding is done to a spare (apartment) key. not to the bridge.
    could that be the problem?
  6. Is the key only connected to the tone pot? Where does the ground from the output jack connect?
  7. mahrous


    Aug 13, 2005
    pickups: both grounded to the key

    volumes: grounded to the back of its pot

    tone: capacitor from the right ring soldered to the back of the pot then the back of the pot is connected to the key

    output jack: grounded to the key directly.

    thanx for the help :)
  8. When you say that you've grounded the volume to the back of it's pot I'm not sure what you mean. Is the back of the volume pot connected to the output ground in some manner (ie through the key)? In order for the volume pot to operate properly it must be properly grounded, otherwise it will not be a volume pot.

  9. mahrous


    Aug 13, 2005

    the volume pots are not grounded to the key. should i do that?
  10. FBB Custom

    FBB Custom TalkBass Pro Commercial User

    Jan 26, 2002
    Owner: FBB Bass Works
    If the volume pot casings are not grounded, then connecting the "ground" lug of the volume pot to the casings is not going to connect that lug to ground.

    Was there nothing around the house you could have used besides a spare key?
  11. Yes, the volume pots must be grounded. If the key is the only thing connected to the output ground then the volume pots must have a connection to it, either from the outside lug on the pots, or if you've connected the outside lug to the back of the pot, then from the back of the pot.
  12. mahrous


    Aug 13, 2005
    give me an idea of what to use and i will use it

    i thought the key was a good idea because i can screw it to the cavity in the keychain hole.

    i am currently in school now. when i am back home, i will ground the volume pots. thanx for the help :)
  13. I like to use a large ring terminal to bring all my grounds to and then out to ground on the jack.
  14. mahrous


    Aug 13, 2005
    how do you 'out to ground on the jack'?

    i thought the jack needs to be grounded not to ground to!
    please explain.
  15. I don't know what you mean by grounded not to ground...

    The jack has two lugs on it (or three if it's stereo). One of these is what you would call signal (some call it "hot"). For a vol/vol/tone setup the signal will be coming from the outside lug of the tone pot where the other two volume pots are connecting. The signal connects to the lug that is connected to the "feeler" that touches the tip of the male plug on your patch cord. The other lug on the output jack is for ground. This lug should be connected to something to which you have brought all of the other grounds (the two pickup grounds, the two volume pot grounds, the bridge ground and the tone pot ground). For this I'll use a ring terminal. I personally like to avoid using the back of the pot to ground things as this can potentially lead to ground loops which can act as an antenna and pick up unwanted noise.
  16. mahrous


    Aug 13, 2005
    ok i pretty much understand all ur saying now.

    i have grounded both volume pots. hum is gone for good (except for a tiny bit which i believe will be gone when i get my shielding paint from stewmac). the volume knobs work properly now, can turn down the pickups too.

    i have done exactly what u said to the jack. it just seemed correct for me from the first time i wired it.

    thanx for the help. i guess i will be posting more in this thread when its time to wire the Aguilar in my next bass :)