Parallel P preamp idea

Discussion in 'Pickups & Electronics [BG]' started by mrbell321, Jul 22, 2013.


  1. mrbell321

    mrbell321

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    I've got an idea and I'm wondering if it's been tried before. I've got a bass that I use for testing things out. I've never tested out preamps like this, but I do have a half-decent understanding of electronics.
    P's have 2 coils traditionally run in series, but sometimes parallel. P's often don't have preamps, but it would be interesting to see how that works out. BUt not just any preamp. I thought it would be interesting to build a preamp w/ 2 buffers, 1 for each pickup. This would isolate the two coils so the impedance/capacitance of one would not kill the overtones of the other. The two signals would then be mixed and potentially amplified because I am also considering underwound coils to really bring out the top end. Between the mixer and gain stages, I would put the tone controls

    I know a lot of people like the P for it's thump. I think this would retain the bottom end, but it would add some zing to the top. The tone controls can be used to dial it back down if I want a real low end.

    So, has anyone ever tried this? What do you think?

    BTW, the seed for this idea came when I ran across a cache of surplus good quality quad op amp chips and I thought "What can I do w 4 op amps in one circuit? Ah, buffers, mixer and gain!", so I won't be out anything except time for trying.
     
  2. line6man

    line6man

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    Isn't that how the EMG split coils are?
     
  3. walterw

    walterw Supportive Fender Gold Supporting Member

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    i think so, yeah;

    i'd be more interested to hear this on a J bass, where the two pickups each carried all 4 strings; to really hear a P-sounding neck and a barky bridge at the same time, rather than the normal mid-scooped "3rd sound" created by the two passively loading each other like normal.
     
  4. joelb79

    joelb79 Supporting Member

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    You just described an EMG P.

     
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  6. mrbell321

    mrbell321

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    Ah, I was not aware of this. I looked at EMG's site(and every other pickup maker I could think of) and they generally don't seem very forthcoming w/ technical details. To read the marketing, they've all cured cancer, but they're not going to tell you how.
    ...That or I'm too much of an idiot to understand what they're saying.
    Either is possible...
     
  7. mrbell321

    mrbell321

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  8. mrbell321

    mrbell321

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    Also, I agree, this would be interesting on a J, but my current test bass is a P. If it works out reasonably, well, I might try something on a J.
     
  9. iiipopes

    iiipopes Supporting Member

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    It is also how Rickenbacker wired their John Kay 381 model, with each coil having its own buffer preamp.
     
  10. mrbell321

    mrbell321

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    The diagram for that Ric:[​IMG]
    is somewhat close to what I've sketched out.

    After the buffer sections, I was going to do a mixer(separating bridge & neck for treble and bass like this doesn't apply to a P), then a tonestack before the final output gain stage.
     
  11. joelb79

    joelb79 Supporting Member

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    100% positive. Everything about an EMG P is parallel, each set of coils even has a stack design that is wired parallel, and then wired parallel to the other pickup, which houses the dual preamps for each set of coils. those are combined in parallel and sent down the pickup lead to the parallel wiring of the pots in the cavity.
     
  12. mrbell321

    mrbell321

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    Interesting... I'll have to see if I can find a bass around w/ EMG P's... see if that is something I like.
     
  13. walterw

    walterw Supportive Fender Gold Supporting Member

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    so you're saying it's parallel? :)

    i'm pretty sure the EMG P is two RWRP single coils (not stacked) that get mixed inside the pickup, then sent on down the wire.

    emg Js are stacked.
     
  14. joelb79

    joelb79 Supporting Member

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    Mixed but parallel and not two RWRP coils in series like a normal P. I thought though that each set of coils had their own preamp to do some EQ/Signal tricks with the D-G strings. Read that on here; so take it FWIW.
     
  15. walterw

    walterw Supportive Fender Gold Supporting Member

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    they're RWRP one coil each (for hum-canceling), and i think "mixed" means neither series nor parallel.

    i don't think there's any special EQ for one side or the other (although that sounds like a really good idea) because in all the years i've been installing these and through all the different revisions i have never seen any hint in the instructions or on the pickup itself as to which coil was meant for which side.
     
  16. mrbell321

    mrbell321

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    That's a very good point on the ambiguity of which side is which.
    Also, one danger of EQing the sides separately is that you could EQ the humbucking out.

    If they are mixed but parallel inside one pickup, that would require the buffer circuit in the pickup itself. The reason to do it would be to help reduce noise being picked up in the wires. But the reason not to do it would be expense and extra complication. I don't think the noise you'd pick up in the 5" or so of wire would be anything close to significant.

    I think I'll just have to go ahead and build this and see what happens...
     
  17. walterw

    walterw Supportive Fender Gold Supporting Member

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    and that's what EMG does, puts the buffer circuit right inside the pickup housing. new EMG P pickups have the quick-disconnect clips between the two coils; one coil has just two connections to get it into the other coil, where all the "guts" are, including a summing input or whatever for the two coils.

    i've had an idea for differently-tuned P pickups, but don't know if anybody's already tried it:

    i think you can sort of "tune" a pickup coil by the shape of its winding, even with the same number of turns (which is what matters for hum-canceling); what if you wound the EA coil to be taller and skinnier (for increased treble attack) while winding the DG coil wider and flatter, for a fatter, smoother sound?

    that might make for a more "even" P-bass sound.
     
  18. Stealth

    Stealth Supporting Member

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    I'm not certain which method EMG uses, but they can follow the "series, then buffer" design, "buffer, then parallel" design or the "differential coils" pickup.
    • "Series, then buffer" is the easiest, but then you don't have much of a difference between having a preamp on board one of the pickup coils and a regular P with a preamp.
    • "Buffer, then parallel" is, if I recall right, the default EMG route. Note that you cannot wire the output of a preamp into another coil and then the input of another preamp, you'd be connecting a buffered coil in series with a (yet) unbuffered that has ten times the impedance.
    • "Differential coils" is the EMG route for the 81 guitar pickup. One coil goes to the inverting side of the op-amp, the other to the non-inverting side of the op-amp, making the op-amp attenuate the common-mode noise very efficiently and making the pickup very much noise-free. This guy tells it as it is and explains it very well..
     
  19. mrbell321

    mrbell321

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    Oh yeah... differential op-amp. Duh. That's a good idea.

    Now I have to find a use for my quads....
     
  20. mrbell321

    mrbell321

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    Hmm... so. I'm having a really bad day, so I might not be thinking straight. But using an opamp in differential mode like that is actually problematic for coils that are designed to be humbucking in the first place(ie RWRP).
    Ignoring active electronics for a moment, hum in a parallel RWRP setup is NOT common. It's a humbucking setup because the hum is exactly opposite, and therefore destructive.
    Back to the opamp in differential mode will try to minimize the common signal and amplify the difference, so you'd actually end up with MORE hum than you would in the first place.
    This could be remedied with 2 of the same polarity, same direction coil, but I wasn't planning on winding my own pickups just yet...
     
  21. mrbell321

    mrbell321

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    ...Altho... I think that assumes you keep the "polarity" of the pickups in the same position they would be in series. Polarity being completely arbitrary to the overall circuit, but important as a relationship between the two pickups. I think maybe you could reverse the polarity of one pickup in relation to each other and get your common signal back together.
    That is, if you had a standard 2 coil set of P pickups, you could cut the wire between the pickups and choose that as ground. Then the "outer" wires would be your independent signal lines.

    I think....
     

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