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pickup experts: half out-of-phase phenomenon

Discussion in 'Pickups & Electronics [BG]' started by Schwinn, Aug 29, 2004.


  1. Schwinn

    Schwinn

    Dec 4, 2002
    Sarasota, FL
    I recent redid the electronics in my Carvin bass: Bart jazz, MM and NTMB preamp. I am very happy with the results!! I used the bass for a gig last night and it sounded great. I really like the MM pickup the best. I wired it for parallel/single coil/series which is really cool. I mostly use it set at parallel or single coil.

    But all is not perfect :( . When the blend pot is centered the B, E, and A strings sound ok, but the D and G strings sound weak, like they are out of phase. Turning a hair to the right or left restores the sound, so it is only on the center detent. This is a new blend pot. I had other problems with the old one, but it was also doing something similar except it was happening at different points on the pot.

    One thing that I think is relevent is the jazz pickup is actually a bridge jazz that I'm using as a neck pickup. I've always had to reverse wire for this pickup when I've had other preamps in the bass (the stock one, and the aguilar). I think this detail may have something to do with it, but I'm not an expert. Maybe because it is wound to be a bridge pickup, it's not compatible with another bridge pickup? I don't know. This isn't so much of a problem, but I'd like to know if there is a fix...thanks!!
     
  2. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    Wassup again.

    FWIW:

    Been a while since I've dinked with the pot thing but recall when I had two volumes with an out of phase relationship the volumes had to be balanced to knock out the phase. The more off they were the more pronounced the out of phase tone. So I'd guess you'd have the same situation with a blend, which logically should be balanced in the middle. Sounds like you're saying the jazz pup is currently wired out of phase. So you'd swap the J pup wires to stop it as you'd done before.

    I can think of no reason putting a bridge in a neck position would have any affect. You should just end up with a generally darker sounding neck pup than it would normally be.

    I've not found any use for an out of phase tone personally and it's been more of an irritation than anything. There are easier or more controllable means to obtain a thin tone.
     
  3. Schwinn

    Schwinn

    Dec 4, 2002
    Sarasota, FL
    bump for curiousity's sake
     
  4. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    Sorry, me again.

    You know, it may have been just the opposite. The pups canceling more as they became of equal volume. Been a while but it did one or the other.

    Is that jazz pup are quad or split coil by chance?
     
  5. Schwinn

    Schwinn

    Dec 4, 2002
    Sarasota, FL
    Hi Ron,

    I don't know about the jazz, I think it is a single coil (bartolini 59j). That's about as much as I know. I would try reversing the wires of that pickup, but there is only the hot wire and the braided shield so that wouldn't make sense. I tried reversing the wires on the MM before without much luck and the wiring for that one is complex and soldering is a pain in the butt! Everything going to a tiny switch. I don't know, the bass is my backup so I'm not too concerned, just more curious than anything. Thanks...
     
  6. Metal Mitch

    Metal Mitch

    Jul 14, 2003
    NJ
    What's up Schwinn! This is weird because I had the exact same problem on my BC Rich, and just solved it yesterday. :D

    With both volumes up full I was getting 1 coil (half the strings) out of phase, and when I backed off a bit on either volume control the output was restored. I tried reversing phase on one pickup, and then the other coil became out of phase. So I spoke with DiMarzio tech support and they figured the magnets were probably installed in the wrong direction on one side of one pickup. But they couldn't say for sure without seeing it.

    So I ripped out the J and jumped in my car.

    Unfortunately, I had assumed incorrectly it was the J pickup causing the problem. The tech at DiMarzio tested it and it was fine. At least I knew the problem was with the P.

    I went home planning to temporarily replace the P until they re-opened next week and could take a look at it. When I took out the P, I found the glue on the BCR pups was so old and dried out that the magnets actually fell out of one of the P coils. I figured now I was really screwed because I didn't know which way they went back in. Oh well, I'll just have them put it back together for me next week, right? Wrong!

    Luckily, I just happened to have another DiMarzio P/J set waiting to go into another bass. And not being one to give up easily, I matched up the magnets with the other P. One by one, I tested for repulsion/attraction so they would line up exactly the same way. First I fixed the coil that had fallen apart and glued it back together. Then I tested the other coil, which had been the problem coil from the beginning. Sure enough, ONE of the 2 magnets on that coil didn't match the other P. I flipped it around, glued it back in, and the phasing problem disappeared.

    This was very easy with the DiMarzio because the 2 bars are located on the bottom of each pickup coil. I don't know how the Barts are constructed so it may be more difficult with those. But if you can get your hands on another set (maybe by going into a local shop) you might be able to pull each magnet and match it up against a working pickup. Or get a diagram from Bartolini for the correct polarity of each magnet, and test it using another magnet. If you don't want to mess with that, you're looking at a return for repair to flip the improperly installed magnet.

    Good luck!
     
  7. luknfur

    luknfur

    Jan 14, 2004
    DIXIE
    FWIW,

    MM that was some good work and a good demonstration of the some of the wierd things that occur in assembly. But the barts probably a blade magnet and they're epoxied so you don't tear into a bart and use it afterward.

    Schwinn, I'd try a couple things. It does seem wierd but a wires a wire and I'd reverse the J leads and check the response. Then I'd try installing two volumes instead of vol/blend. I don't think either will make a difference but who knows.

    Ya know, I've had lots of Bart J's and I don't ever remember having a Bart J with a shield and a lead. Usually it's two leads with one of the post grounded off the lead.

    Also, have you checked the magnet with a piece of metal? That should tell you how far the magnet extends and the strength.

    Another thing is flipping the pup around. You should get the weak response on the low side but who knows. If not, you know the pickup is fine at least.

    I'd also so try skipping that switch and hard wire the MM in series. You should get the same response as with the switch but who knows.

    You could also drop another J in to see if it makes any difference.

    Bascially, you just have to do something different and check response till you either get the results you want or figure out what the problem is. To isolate a problem you have to isolate a part.
     
  8. Schwinn

    Schwinn

    Dec 4, 2002
    Sarasota, FL
    Hey Mitch, that was a great story and I can see how this might be a magnet issue too. Thanks.

    Luknfur, I will try some of your suggestions I think. Maybe not right away but when I have some time on my hands. I already thought of turning the J pickup around as an experiment but the lead isn't long enough. Thanks.