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PBass wiring. Help!

Discussion in 'Pickups & Electronics [BG]' started by jeffbrown, May 4, 2010.

  1. OK, so I finally decided to dig into my Epiphone PBass clone to see if I could at least cut down on the hum, and also find out why my tone pot was also affecting the volume. I downloaded the "Standard P-Bass" schematic from the Seymour Duncan website. May I add that I am NOT any kind of electrician, nor do I play one on TV? I would greatly appreciate the accumulated wisdom of this forum.

    I am assuming - dangerous, I know - that the SD schematic is "looking" at the pots from the bottom to illustrate the soldering points on the pots. Please bear with me.

    Here's what I found:

    1. The volume pot is labeled "B500K (the symbol for) ohms"; the tone is labeled "A500k (the symbol for) ohms". (Obviously, NOT 250k.)

    2. The cap is labeled "2A683J".

    3. Looking at the SD schematic, the white wire from the pup should be attached to the left "point" of the volume pot, which should then jump to the tone pot. Mine is on the center, *no connection to the tone pot*. The center point also has no jumper to the tip of the output jack.

    4. The black wire from the pup should be soldered to the body of the volume pot, common w/the grd from the bridge, the jumper to the tone pot, and the right point. My black wire is soldered to the body of the pot, common with the left point (again, no jumper to the "point" on the tone pot from here), and the jumper to the body of the tone pot, no jumper to the bridge. The right point has a short jumper soldered to the body of the pot.

    5. The jumper from the common solder point on the body of the volume pot to the body of the tone pot should share a leg on the cap, which then goes to the center point of the pot, and a jumper to the sleeve of the output jack. Mine goes to the body of the pot, shares a leg on the cap, which then goes to the center point of the pot, and also jumps to the left point of the pot. The jumper to the sleeve is there. The right point of the pot is open.

    6. The jumper from the bridge is connected to the sleeve of the output jack. It is the closest point from the bridge, and does make the ground. What, if any, advantage would there be to moving it to the body of the volume pot? Most curiously, there is also a jumper from the sleeve connection to the tip connection. That I REALLY don't understand. There is no other connection to the tip.

    There is a metal-looking tape thing on the underside of the pickguard where the controls come through. There is no shielding in the cavity, only a black paint of some sort.

    This is my first foray into the innards of this, or any, bass. I like the way it plays, and I can't afford a new bass right now. Should I change out the pots and/or the cap/attempt to rewire it correctly? I plan on getting some copper tape to line the cavity.

    TIA! This forum has been a wonderful resource for me, and I look forward to your suggestions.
  2. I assume you mean this:


    Maybe it's just because I'm knackered, but I'm having a hard time visualising what should be simple here. Any chance of sticking together a diagram. And another thing to take into account is that there are several ways to skin a cat, so to speak.

    Also, if there is a jumper cable from the jack socket sleeve to the tip, this would be sending everything to ground. So, basically I'm confused :p

    A lot of basses use a black shielding paint, tho you can always replace this with some copper or aluminium foil if you want.
  3. B is linear taper, which should have a smoother control than audio taper when used as a volume. You should stick with audio for the tone control though. 500K is a bit brighter/hotter than 250K.

    That's a 0.068uF cap. I don't think I've ever seen that value on a P bass.

    0.047uF is the standard value. A 0.068uF cap would just cut more treble.

    If both the pickup and the output are on the same terminal, the volume pot has no function.
    You just have direct-to-jack wiring.

    There is no advantage or disadvantage. It's simply a matter of wherever is easiest to ground the bridge. As long as everything is grounded, it doesn't matter how you do it.

    If there is a connection from tip to sleeve, you should have no output. I'm not sure why anyone would do such a thing. They obviously have no idea what they are doing.

    The black paint is likely conductive shielding paint. Is there grounded metal lug screwed down in the cavity somewhere?

    You should just rewire first, then see if there are any problems that require the parts to be replaced.
  4. Arvin

    Arvin Underwound Supporting Member

    Sep 26, 2008
    On the bench
    The Squier Classic Vibe 60's P-bass has a .068uF cap in it (at least mine does). I like it -- it pushes the "slightly rolled off" tones to the upper end of the pot's excursion, plus it gets very swampy at the lower end.

    I've got a couple of basses that I think would benefit from more capacitance in the tone control, so I'm going to experiment with .068's and .1's and see what I like best.
  5. Ah.

    Well, capacitor values are usually a personal preference, but the standard/most common value on most Fender basses is 0.047uF.

    Capacitors are dirt cheap to experiment around with.
  6. Arvin

    Arvin Underwound Supporting Member

    Sep 26, 2008
    On the bench
    Yeah, I was surprised when I opened the bass up and it wasn't a .047 in there. Someone in the design dept. at Fender/Squier must like bigger value caps, too -- I doubt it was an accident.

    Anyway, I'll quit hijacking the thread. :ninja:

    My $.02 about rewiring/replacing components? The only component I routinely replace in budget instruments is the output jack, merely because I've seen so many cheap ones fail (mechanically). I like to put a well-made (sturdy) one in right away, to avoid problems later. This may be overcautious overkill, but I'd hate to have a jack fall apart on me in the middle of a gig. As to the rest of the stuff, if it ain't broke, I don't try to fix it.

    Good luck with your bass, jeffbrown.
  7. Thanks for all the input! The wiring diagram I was referring to I found at:


    I finally got up the nerve and, using my trusty Radio Shack soldering iron, rewired it to this spec. Incredibly, I didn't break anything, and the bass now actually performs the way it was intended. It still has a slight hum when I'm not touching anything metal on it, but from what I gather, "They all do that."
  8. mndean


    Mar 20, 2009
    Good thing I found this thread. I developed a slightly different problem with my '80s Squier P-bass clone and found that someone got at the wiring before I bought it, so I'm going to replace everything (I've never been happy with the pup, it's a lot duller than my SX clone's pup) and rewire it myself.
  9. mndean


    Mar 20, 2009
    Just to follow up, I found that the wiring was in an array of colors I'd never seen before (red, yellow, and traditional black), the two "halves" of the P pickup had a taped solder joint on the wire between them (is that normal?), both pots were linear taper, and the jack was soldered strangely. Soldering was pretty bad (globs of solder with spatter all around). However badly the job was done, it worked until just recently. Haven't removed the bridge to see the ground connection yet.
  10. LoveThatBass


    Jun 28, 2004
    Wire it per the Seymour Duncan drawing.
    Second, I along with most others disagree on what was said about the Linear pot vs. the Audio Pot.
    Since our Ears hear logrythmically the Audio Pot being somewhat of a Logrythmic pot will counter this effect but the Linear pot will give the effect of turning the volume down very quickly with the first 25% of the pot then very little after that as it will sound like a switch somewhat where it turns on and off fairly abruptly. Notice the 250K A on the Seymour drawing. That a is for AUDIO pot.
  11. But have you actually tried linear taper volume pots?
  12. mcapote


    Sep 9, 2009
    Miami Florida
    maybe they went with the bigger cap to make up for the 500k pots instead of 250s. personally I liked 250k pots and .1uf caps on my pbass, but I also prefer the SPB-3 sound over the brighter pickups
  13. MglMatador


    May 5, 2010
    Line6man is absolutely correct. Linear taper works much better for volume on a bass and gives a finer control over the sweep versus perceived volume.

    I'm guessing this is because of the very low fundamental frequency range of the bass, who's fundamental really only spans from ~30Hz (low fundamental B) to ~450Hz (highest notes on a C string). Even counting first and second order harmonics most of the frequency content is below our sensitive hearing range. This is why the tone pot still works best as an audio taper, because you are in effect sweeping the harmonics where our hearing is much more sensitive. Even if you want to argue technical grounds it behooves you to try it out and you'll be surprised.

    Even an exponential function looks linear if you look closely at the beginning of the curve. ;)
  14. LoveThatBass


    Jun 28, 2004
    Lineman6, my experience with Linear pots have been as volume pots in some of the newer Fender amps where you turn it up 1/3 and it sounds incredibly loud then not a lot of change after that. Myself as well as others feel Fender did this so the customer who tries one out at say Guitar Center might go "wow, listen to how loud this is at 1/3" knowing they wouldn't crank it any higher at a store.
    If you have actually tried this on a bass volume and state it works differently I may give it a try.
  15. Depending on where/how it's wired into the circuit, an amp's volume control is entirely different from a bass' volume control.

    You're comparing apples and oranges.

    Try a linear taper volume pot in your bass, and I can almost guarantee that you'll love it.
  16. walterw

    walterw Supportive Fender Gold Supporting Member Commercial User

    Feb 20, 2009
    and that's exactly the difference in application. on a crunchy, compressed guitar, a linear volume will indeed leap up annoyingly from "0".

    on a typical clean bass, a linear volume will be perfectly even from "10" to "0".
  17. LoveThatBass


    Jun 28, 2004
    Interesting! Thanks

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