Ok, so what exactly is a Dummy Pickup?

Discussion in 'Pickups & Electronics [BG]' started by Flux Jetson, Dec 10, 2012.


  1. Flux Jetson

    Flux Jetson

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    I've asked some questions about this before but I didn't phrase them right, so I went away with a zero understanding. I'm totally not getting it. So let me start completely over.

    What is a dummy pickup? Is it a pickup with no magnets?

    I understand what they're used for sometimes, to keep the humbucker effect going on when soloing a single coil pickup (which is something that appeals to me, I use just the neck pickup about 50% of the time, the other 50% I have neck and bridge at full volumes). But how is it wired and what exactly is it? Is it a regular pickup that's been wired in to the bass electronics in some clever way? Or is it a specially prepared pickup, like one with no magnets or something? Does it really make no sound at all? And how is it wired in?

    Thanks for suffering through my ignorance :) I most surely appreciate the help.

    Fluxiod.
     
  2. AltGrendel

    AltGrendel Supporting Member

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  3. bassbenj

    bassbenj

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    Yes. It's a pickup with no magnets. (in other words just a coil of wire), hence often called a "dummy coil". It's purpose is to pick up hum. In fact to pick up the SAME hum that the solo pickups are sensing making them hum. When the hum level from the actual pickups and the Dummy pickups are equal, you can wire them in series so that one cancels the other. Since both are picking up hum, the hum gets cancelled out, but since only one is picking up strings that goes right through. Clever.

    But what is NOT so clever is that the second coil in series DOUBLES the inductance of the pickup system which can change the tone quite a bit. This is why Alembic and other basses using a dummy coil mix it in electronically rather than by a simple series connection. In that way hum is still cancelled but the tone isn't changed.

    Does this make sense?

    Humbucker pickups do the same thing only in that case it's TWO pickups, both with magnets that pickup the strings. These are also wired in series to cancel hum. And that would normally ALSO cancel the signals from the strings, only they reverse the magnets on one of the pickups so that it puts the string signals back in phase so they add rather than cancel. Voila! "Humbucker". The only problem here is that now the pickups are sensing the strings at TWO points instead of one giving a "fatter" tone, (which is why some refer to humbuckers as "mudbuckers")

    OK?
     
  4. kurosawa

    kurosawa Supporting Member

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    This problem is overcome with a large coil (Lindy Fralin says it's the only thing that works): http://ilitchelectronics.com/

    For a jazz bass, both pickups would be wound in the SAME direction, with the oppositely-wound large coil providing hum cancellation.
     
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  6. SGD Lutherie

    SGD Lutherie Banned

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    They don't have to be in series, they can be wired in parallel. They just have to be out of phase with each other.

    The best way to do a dummy coil is with an active system to keep the string sensing coil isolated from the dummy.
     
  7. SGD Lutherie

    SGD Lutherie Banned

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    And with the same magnetic polarity.
     
  8. Stealth

    Stealth Supporting Member

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    The rest of your explanation is bang-on, that's the logic behind the humbucking concept. This definition is the only thing that's not exactly right. The "mudbucker" name is usually associated with a very high-impedance pickup (very close to 30 kΩ - triple what's normal for a pickup) which is a sidewinder humbucker - coils lay flat on their sides with a central metal plate and a set of screws. That one senses the strings in a narrow line in the center where the coils meet (or, if you will, in three points, since you have the center point and the two other edges of a coil), but still acts as a humbucker due to the magnetic and electric polarity. The "fatness" comes from its position (underneath the 3rd harmonic of the string) and its high impedance, but I don't know so much about its multiple sensing points. I hope SGD can clear that last part.
     
  9. SGD Lutherie

    SGD Lutherie Banned

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    OK, humbuckers sound fuller for a few reasons. One is they are sensing the string in two locations. This does a couple of things; it reinforces common frequencies, so you get more lows and mids, and it cancels some upper harmonics. As you move the two coils farther apart you change the frequency of the notch. You can hear this on a Jazz bass with both pickups on.

    Humbuckers also have higher inductance if they are wired in series, unless you wind them on the lower side.

    A mudbucker is an entirely different animal. The Gibson mudbucker is actually a sidewinder design, so it senses the strings in a single location as a single coil would. But it's so over wound as to remove most of the high frequencies. Sidewinders can be made to sound just like single coils with no hum.
     
  10. Flux Jetson

    Flux Jetson

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    Ok, great ... I'm with everyone so far.

    Now let's throw my bass into the situation. My J has a setup where each pickup has it's own output jack. No tone controls, just two volume knobs, each one assigned to each pickup, then straight out to two dedicated output jacks.

    That said, is there a way to concoct the active electronics outboard of the bass? Somehow create a "box" with the 3rd coil in it? Or if that is a no-go, then put the 3rd coil back in the bass and create the active electronics in the outboard box to do the tonal "corrections" so to speak, that have been mentioned already?

    Would this take a pickup switch or perhaps a 3rd output jack to keep as much of it all out of the bass?

    This notion is all part of a research system I'm using (see sig). So that is why I'd like to keep as much of it all off-bass if possible.

    Thanks for the help do far! I'm leagues more informed than I was when I posted this thread. :)

    Fluxhole.

    Oh .. here .. this is the basic chain:

    ** Pickups
    ** Output jacks
    ** Two individual mic preamps to provide a HiZ input stage for the pickups (840k input Z). Note that the mic preamps have phase inversion switches.
    ** A foot operated switch that allows me to footswitch between two preset pickup settings on the fly. The two settings I use are 1.) both pickups fully on. 2.) Neck only.


    As a side note, the footswitch is a short-action momentary that is a dead-silent switcher, no pops or clicks. It allows me to instantly switch between those two pickup settings in the middle of a phrase or riff. Handy for getting a good tonal balance between the thin strings (D and G) and the thick strings (E and A). I typically use both pickups for the E/A strings and the neck only for the D/G strings. It took some practice to learn to use this rig, but it sure sounds great! Since I have full control over the pickup levels I have been able to make the (both pickups) and (neck only) settings have the exact same ouput levels, so other than tone changes the two settings have identical output levels.

    There, that's all of it. Don't know if any of that is pertinent but there it is.
     
  11. Ric5

    Ric5 Supporting Member

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    Yes ... but you can also wire the pickups parallel and still get the humbucking effect. With parallel you get a smoother scooped out tone like a jazz bass.
     
  12. kurosawa

    kurosawa Supporting Member

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    @David: OK, it's OT (well not totally 'cause I know the answer's gonna involve pickups), but man, I love that sound you're getting on "Do What Makes Your Heart Sing (Part I)." What do you have going on there?
     

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