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Bartolinis xxM56C wiring issue - only thing pending to finish a build

Discussion in 'Pickups & Electronics [BG]' started by octaedro7, Jan 24, 2014.

  1. Hi all.

    I was hoping someone could help me figuring out how to wire these pickups as the Bartolini wiring schemes do not cover them. This is the last thing I need to sort to finish my build :bawl::


    As the title says the Barts in question are a set of XXM56C quadcoils that I bought from fellow TB member.

    The intended wiring is having each pickup splittable by means of a SPDT mini switch so to get:

    Rear Stacked Coils – Full Quad - Front Stacked Coils

    The pickups go through an Aguilar OBP3 with a frequency selector (400Hz-800Hz) and with an active-passive switch. I have installed the preamp once before so I’m positive it’s fully working, never tried the pickups though.

    Now as if things were not already complicated I decided to install the switches as I did in my first prototype, that is instead of drilling an 8 mm hole and fix the switch with its nut and washer, I leave the top thicker and drill a 7 mm hole so that I actually screw-in the switches so that only the lever rises above the surface.


    The effect is really cool (IMO) but of course makes things way more complicated to wire (and also a bit messy on the eyes, but we all have messy guts, haven’t we? :D). So to achieve this I have to prewire all switches and after they are all in place I wire them to the pickups and the preamp.


    One thing I should mention is that, since I did not have any SPDT switches, I used 2 DPDTs (on-off-on), but just one half of each (the 2 leftmost on the pic). I read that it is equivalent. Hope that this is not the issue…

    Now the first issue that I encounter is that the pickups are supposed to be quadcoils but they only have 4 conductors + shield. When I check the Bartolini site (which has been recently renovated BTW), the wiring scheme associated to them mentions 6 conductors (!?)
    So I assumed that the wiring scheme for Dual coils with 4 conductors will give me the desired splitting:

    BTW: The wires' colors of my pups match perfectly the diagram above

    Thing is that after wiring everything (took me quite a lot of time) I plugged it in and cha-cha-cha-chaaan-



    So at this point I’m thinking that the pickup wiring is wrong but I don’t know how to troubleshoot it in a way that I don’t have to unwire the whole thing.
    I would be really grateful if someone can point me in the right direction. If pictures of the actual wiring are helpful please let me know.

    Thanks in advance

    BTW: I have read already a couple of threads covering troubleshooting, but they refer to simpler layouts.
    I’m also very curious as to why there are no wiring diagram in the manufacturer’s site that matches the model that I have…
  2. JustForSport


    Nov 17, 2011
    Check these- same diagrams as before, but new site layout, as you said.
    Also, to double check coil layout-
    using a cut-off E string or similar, moving the tip across the face of the pickups (letting the magnets pull the tip down)
    will show the gaps between the quad coils, or if no gaps, then dual-coil rails.
    From somewhere on Bartolini's old site:
    "Nearly all of the large soapbar shapes are available in multiple configurations. Nearly every size is available as Dual Coil (single / single), Dual Coil Split "P", Dual Coil Split "reverse P", Quad-Coil (with switching available for all of the above configurations) and Quad Coil (4 singles in line)."
  3. Thanks but those are precisely the diagrams I'm mentioning. The first one is for 6 conductor quadcoils and the latter is for 4 conductor dual coils.
    The packaging of my pickups said xxM56c, which are described as quadcoils, yet mine have only 4 conductors + shield.
    I'll try sensing the coils but the thing is that I've already tried the dual coil wiring to no avail. So apparently they are not duals.
    Can somebody advice on what would be the wiring to connect the pups straight into the jack, considering the number of conductors my pups have?
    I want to discard faulty pups.
  4. JustForSport


    Nov 17, 2011
    I just provided those for comparison of the terminal arrangements they used.
    Are a couple terminals jumpered on the back plate to a default coil layout, resulting in 4 leads to hook up?
    Sometimes the jumpers can be bypassed/ cut to provide different coil selections.
    Sensing the coil layout can help determine the terminal groups for the coils, but using a meter to measure the resistance between them is the only real way that I know of. Measuring with jumpered terminals likely will not give the whole story.
    You may also use alligator clip jumpers to a jack and test them that way. Again, jumpered terminals will have two coils connected, but testing can be done as if 'coil-split' mode.
    Those may be quad-coils, just pre-wired in 'P' or 'reverse 'P' mode which can be changed as you want with the jumper removed/ cut and selected with your switches.
    Any photos of the back plates on those?
  5. Thanks again JustForSport, I'll post pics ASAP

    Found pictures of the pups backs here and a coil diagram on a vendor webpage:



    The site where I got the coil diagram from states that they are splitable into p and reverse p modes (not exactly what I wanted but still ok).
    The thing I'm worried about now (apart from having faulty pups) is the chance of not being able to split them, leaving the bass with 2 useless switches....

    I do have a meter. I'll check them out and post back my findings
  6. JustForSport


    Nov 17, 2011
    Without a furnished wiring diagram, a meter is the only way to determine each coil 'start' and 'end' terminals (bare wire included).
    It's likely that since 'P' and reverse 'P' are RW/RP, that a splittable dual-coil config would not be hum-canceling.
    Hopefully, someone will come along that's had more experience with these, and can maybe provide a schematic.
  7. JustForSport


    Nov 17, 2011
  8. Dirk Diggler

    Dirk Diggler Supporting Member

    Mar 3, 2004
    Anytown USA
    Well I can personally guarantee those pickups were never used or installed ever, so it's not the pickups, unless something happened in shipping, but that's doubtful. That said I've never gone that elaborate with wiring them before.

    If I were to guess it's your switching that would be suspect.

    They are indeed quads and they indeed can be split, I have a bass with that exact setup, well with a Bart pre.

    Hopefully someone may have an answer for you.
    I'll see if I can dig through my old paperwork and try and find a diagram for them.
    Good luck,
  9. Dirk Diggler

    Dirk Diggler Supporting Member

    Mar 3, 2004
    Anytown USA
    Ok here's what I found in my closet of documents, hopefully this will get you going in the right direction. I'll leave it up for a while in case anyone else might need it.

    It's a 2 page .pdf.

    Good luck,
  10. I finally found some time to start doing testings. I have solved 90% of the issue. I'll share my findings in case somebody plans on using these XXM56C pups.

    Bartolini's diagrams for dual coil pickups (4 conductors+shield) do work for these quad coils.

    The diagram of the coils is indeed actual. What I could verify is that they are 2 pairs of 2 in-line split coils put side by side
    I added to the diagram what wires belong to what pair of coils:


    Note that I put there the Bartolini logo as position reference.

    I don't know what exactly went wrong with the former wiring, meaning that I did not spot a clear culprit. :confused:

    Thing is that I manage to have each pickup going through its coil switch and through the preamp. The preamp mid switch and bypass work perfect as well

    For the first time I could hear this baby and it sounds great, lots of versatility.

    Now here comes the trick. If I put the balance pot on center position I get no sound. Soloing any of the pups works ok.

    So I guess I should review the Balance wiring although I'm following to the letter the Aguie wiring diagram. There are however other sources like the stewmac diagrams that show the volume wire and the ground wire switched with respect to the Aguie:


    Anybody knows if I am going in the right direction?
  11. JustForSport


    Nov 17, 2011
    Interesting- good to see you're getting somewhere...
    Most wiring diagrams I've seen have as Aguilar's is,
    ...I just pulled 2 covers and those OBP3's are wired as their diagram, and same as in the attached Bart diagram- and they work correctly.
    Is your bal pot grounded- some don't think it's req'd.
    Also, did you check this link:
    (posts #11 and #12).
    to determine if those can be switched as split 'P' / reverse split 'P' and still be humbucking? Seems they should be.

    Attached Files:

  12. Just reporting back that the trick was to switch the output and ground wires.
    Ironically I found a problem with the finish so I had to take all the electronics out and reapply the finish!
    Thanks JustForSport and Dirk for the cooperation.