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Pickup Routing Question

Discussion in 'Pickups & Electronics [BG]' started by CosmoReverb, Dec 21, 2012.

  1. CosmoReverb

    CosmoReverb

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    (Whoops. I originally posted this in the general "Bass" forum. I probably should've posted it here first.)

    Here's a weird question that I was wondering if I could get y'alls opinion on. I had an idea hit me earlier today and I was wondering if anyone has ever done a passive control scheme as described below and what you cats thought the feasibility/usability of it would be?

    [​IMG]

    So first of all forgive the image I just needed something for illustrative purposes and the quickest thing I had handy was a quick sketch I made a year or two ago of an idea I had for a Lace Alumitone loaded, headless version of the old Fender Performer design. Obviously this idea would work better without the 24 fret neck and the pickup brand is a bit distracting. My question is just about the theoretical control setup illustrated, not about the specific details shown.

    The idea is just for a bass with two standard Jazz pickups and an additional humbucker at the neck. The Jazz pickups route through a blend knob and the humbucker routes through its own volume pot and then the blended output of the 'buckers pot and the Jazz's blend pot then go to a 3-way toggle and then to the tone -> master volume -> output.

    So what do you guys think of that. Has anyone ever produced a bass utilizing a similar setup? I've never come across one but it seems too obvious to not have been attempted. Seems like it would give a pretty wide tonal range in a not-too-complex setup. Is it technically feasible? Is it overkill? Would it yield far more unusable results than it would interesting ones? Thoughts?
  2. sharp8874

    sharp8874

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    Never seen that setup would definatly work well! It could get some cool pickup blends for sure!
  3. ctmullins

    ctmullins Registered 8er Supporting Member

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    I like it. For that much tonal flexibility, I wouldn't bother with a tone pot. And that scheme doesn't really offer any advantage over three volumes - in fact, with the toggle switch in the middle position, I believe it's electrically equivalent - except that the toggle switch allows quick changes (and some folks like blend knobs, I hear).

    But I do like it. I also think it would be cool with the humbucker between the two Js.
  4. CosmoReverb

    CosmoReverb

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    Yeah, quick adjustments would be the primary advantage over a 3mix+1master volume knob setup, that and a cleaner control setup on your bass.

    The tone pots were just there from the original design sketch that I was using to illustrate the proposed setup and were just included because I didn't bother to delete them so they were just gravy. I would imagine that some sort of back-end tone adjustment might be desirable though however since I was imagining this as a passive setup and in the further interest of a more streamlined control layout a single tone knob would probably suffice.
  5. Stealth

    Stealth Supporting Member

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    Actually, the wiring for this shouldn't be too different from the one in a Fender Urge II formerly used by Stu Hamm. It's a J-P-J combination, has a blend for the Jazzes, a toggle for switching between the Jazz blend, the Precision and both, and has a master volume and an active tone stack. The only thing it doesn't have, and you do, is a humbucker volume.

    [​IMG]

    In your case, you'll need an extra volume for the mudbucker - wire it so the pickup connects to the center lug and the output towards the switch (green wire) connects to the outer lug. That way you'll be able to turn it down a bit without turning down the entire bass - that's what your master volume does.
  6. abemo

    abemo

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    One thing to keep in mind is the type of humbucker you use. A mudbucker would be a bad idea here, as the overall inductance (please correct me if I'm using the wrong term here, my scientific knowledge of all this is still a bit foggy) will completely overwhelm the jazz pups (30k vs 7-8k). Something like a MM style might match the jazz pups a little better.
  7. Stealth

    Stealth Supporting Member

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    That is true, the impedance mismatch between the pickups will cause a problem (impedance is calculated from inductance, capacitance and resistance, so you're partially right ;)). I'll explain this using plain DC resistance as it's easy to measure and calculate and is the biggest factor for impedance matching in basses.

    For the maths below I'll assume the Jazz pickups have 8 kΩ resistance. In parallel (averaging the resistances) they'd measure 4 kΩ.
    As you said, the mudbucker has 30 kΩ resistance from its two coils in series (summing the resistances), each at 15 kΩ. Clearly, too much compared to the Jazz, almost eight times as much.
    The MM would run into the opposite problem, as most are internally wired in parallel (again, averaging the resistances) and would measure close to 2 kΩ, that means each coil is somewhere around 4 kΩ on its own. Clearly, not close enough, though it's not as bad as the mudbucker.
    The general idea is to have resistances as close as possible to minimize losses.

    There are a few solutions to the mudbucker woes:
    • Use a different neck humbucker such as a DiMarzio Model One or DiMarzio WillPower Neckr. Their resistance is close to 11 kΩ, and one of ther main uses is in Billy Sheehan's Yamaha Attitude II basses where they're paired with a Precision pickup of similar resistance making for a good blend.
    • Use a regular mudbucker wired in parallel. This brings its resistance to half that of an individual coil, or about 7.5 kΩ. This will take some oomph out of it, but it'll still be deep if it's against the neck like that.
    • Wire the Jazz pickups in a blend-series mode. This is a bit of a complex wiring (I need to redraw it myself, actually) that allows the Jazzes to sum together if they are balanced perfectly (blend in the mid position) bringing resistance to 16 kΩ. This will take away the classic parallel Jazz tone, but will give it a lot of oomph and it'll blend better with the mudbucker.
    • Use an MM wired in series. This brings its impedance to twice that of an individual coil, or about 8 kΩ. This will lose clarity, but if you put it between the two jazz coils, it should have a nice growl to it.

    There's one thing I haven't addressed - the Alumitones themselves. I know you said they were just ornaments in the image above, but I felt like digging around. They're extremely low-impedance pickups, which means they give out a cleaner sound with much more highs then a classic pickup. They have an internal transformer that brings their impedance to "normal" passive levels, however, the transformer doesn't change the inordinate amount of highs received, so they recommend using 250 kΩ pots to tame those highs a bit.
  8. CosmoReverb

    CosmoReverb

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    Wow. Thanks for all of the info! I'm a zero-level novice when it comes to electronics but I did have some inkling that impedance mismatches were a potential problem (although I had no idea that the mudbucker was such a discrepancy to others) but I figured with the huge variety of pickups available that some combination would be a decent enough fit.

    I take it that in your third option since the j-pups would be wired in series that you lose any options for making them cancel each others' hum, correct? Is impedance mismatch still a problem with active systems or is there some way to buffer/normalize impedance when power is involved?

    Thanks for taking the effort to research the Alumitones. Ironic that the example image I used happened to be one of the brands where impedance wouldn't be a problem. You would think that Lace would have developed a better system for taming the inherent high-range of their pickups than to recommend that you just stick a muffler on it (metaphorically speaking.)

    Thanks again!
  9. Stealth

    Stealth Supporting Member

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    Humbucking works both in series and in parallel mode. You have to remember, in order to have humbucking the signals have to somehow add up and the noise has to cancel out. In series the signals simply add, in parallel, they average out, and since noise always has opposing polarity between pickups, it will always cancel out.

    As for the active tone controls, they would still run into the same problem if you used a passive blend before the active circuitry. If you used an active blend - which is basically one buffer per pickup followed by a blend pot - they'd work well. That's actually the general idea behind buffers, not only to isolate the circuits but to ease mixing of input impedances by leveling their output impedance. However, you'd need one buffer per pickup to achieve that, because otherwise you'd have a mismatch again.
  10. CosmoReverb

    CosmoReverb

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    Ah, that makes sense.


    Thanks again!!

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