Which elements make a great guitar pickup?

Discussion in 'Guitars in General' started by Kmaz, Apr 22, 2016.

  1. Ron Kirn

    Ron Kirn Gold Supporting Member

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    Yes... back home in Koln (Cologne) Germany, his stage name was Bill Lorento or something similar.... once he moved to the US, it became Bill Lawrence....

    I don't know if the mention of Bill's changing his name is intended to suggest something nefarious on his part.. But this all was shortly after a bit of an "action" that involved his home land.. Germany... so in the 50's things German typically came under suspicion.I'm sure one or two more perfectly innocent descendants of Germanic origin changed their names too.

    rk
     
    Last edited: Apr 29, 2016
  2. Sweetfinger

    Sweetfinger Supporting Member

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    In the 40s? Rickenbacher changed the company name to Rickenbacker, an ever so slightly more non-German spelling.
    It was his professional "stage name" and was used as a brand/endorsement as well.

    [​IMG]
    [​IMG]
     
  3. Zexcoil

    Zexcoil Vendor

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    Eddy current effects.

    Eddy currents in the pole piece (which is located in the core of the coil) act to oppose the magnetic flux from the vibrating string. If eddy current effects are minimal, you get a relatively "unfiltered" frequency response. AlNiCo5, which is the material used as a pole piece in most Strat pickups, is a good example of a material with minimal eddy current effects. The flux travels as a plug through the pole piece and doesn't get modified much.

    On the other end of the spectrum are the low carbon steel pole pieces typically used in PAF style humbuckers. Low carbon steel has massive eddy current effects, opposing the flux from the string and pushing it into the "skin", or the most outer surface of the pole piece. This filters the frequency response much more significantly than A5, for example. The main effect is a reduction in the Q factor, or peakiness, of the frequency response.

    Note that even in the case of a permanently magnetic material such as A5, it is the properties of the material as a receiver of flux, not as a magnet, that are most important in shaping the tone.

    The most important function of the magnetic field of the pickup is simply to magnetize the string.

    I realize that this is probably a controversial statement, but it's true.
     
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  4. Tone_Terrific

    Tone_Terrific Supporting Member

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    Are you saying that the strings might receive their magnetization in any way, but the the sound varies because the pole pieces have different characteristics and are, coincidentally, the magnetic source for the strings? I know you have mentioned it before but it is still sinking in.

    This implies that changing material of the polepieces can change the sound, however, hb pups will work with no polepieces on one hand, OTOH the magnet is often changed to alter the tone, too.
    NO WAY are pups simple devices. oy!:drown
     
  5. Mr.Strat

    Mr.Strat Member

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    Bill Lawrence Micro Coils --- Are these things basically just like the Leo Fender MFD's, except with a stronger magnet?
     
  6. Blix

    Blix Supporting Member

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    No idea, but if there is any similarities, Leo got it from Bill.
     
  7. macmax77

    macmax77 Supporting Member

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  8. xmd5a

    xmd5a Member

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    I see a source putting the resistivity of AlNiCo 5 at 4.700E-07 Ohm-m, and AlNiCo 2 at 6.500E-07, while 1008 steel is 1.460E-07 Ohm-m. Copper, by comparison, is 1.68×10−8, so the steel is a bit more conductive than the AlNiCo, but I think the fact that the steel has a permeability that is orders of magnitude higher than the AlNiCo, and how that bumps up the inductance, is such a dramatically stronger influence over the overall response curve, that eddy current induced losses are like a drop of water in an ocean of inductance. OTOH, it could explain some of the differences between AlNiCo 2, 3, 4, and 5.

    As far as the eddy currents pushing back on the string, that's an interesting notion I'll have to give more thought to. I know that the coil can induce eddy currents, as any inductor will, but it's interesting to think that string moving string see an "reflection" in the pole pieces, in a sense. Do you think that, if a pickup has a metal cover, that the eddy currents in the cover will essentially cancel out some high frequency flux movement before it even reaches the coil?
     
  9. Zexcoil

    Zexcoil Vendor

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    That's pretty much it.

    Everything in the magnetic circuit will have a similar effect by the same mechanism, but the stuff in the core is the most important. External magnets will also have the same "flux filtering" effect, it'll just be less significant.

    An air coil will pickup a weak signal from a vibrating, magnetized string but that signal will be amplified greatly with a permeable pole piece in the core.

    The magnitude of eddy current effects are determined by permeability and conductivity in equal measure. Inductance (proportional to permeability) drives the position of the peak, and also output, so sure it's important, but it's the eddy current effects that drive the shape of the resonant response.

    Either way, as I said in my initial post, it's the properties of the pole piece dominating the behavior.

    I didn't say that the eddy current effect was to oppose the string vibration, I said it was to oppose the magnetic flux in the pole piece. The magnetic flux is created by the moving magnet (vibrating, magnetized string).
     
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  10. amstrtatnut

    amstrtatnut Member

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    This x 1000.

    Not to say there arent great pickups, just that favorable perceptions tend to lean towards the "good ol days".
     
  11. Sweetfinger

    Sweetfinger Supporting Member

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    A lot of that is simply that almost all the music we love was recorded with them. The character of amplified guitar is the limitations of the electronics. I've said before that if transistors had been invented 10 or 15 years earlier, what we would recognize as "great guitar tone" might be very different.
    I was talking to my rep at Guild a few days ago. He mentioned a new Dreadnought they're bring out and my reply was, "well, you have to have 'em. Lots of people think that a DN is THE definite great sounding guitar". You can invent all kinds of new guitar designs and top bracings, etc., but most players are going to judge your product against what came before.
    Imagine if Gibson/Seth Lover had decided that the new "humbucking" pickup Seth was working on was just kinda "too big", and maybe a little dark sounding and had Seth keep refining the design until he had something like the mini-humbucker and THAT was the design Gibson finally approved and went with as their new top of the line pickup.
     
    Last edited: Apr 30, 2016
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  12. xmd5a

    xmd5a Member

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    I think the eddy currents would actually push back against the string, though maybe not enough to matter. Since that magnetic field of the eddy current would be opposite polarity of the string, it's presence in the coil would also serve to cancel out the flux of the string, so it would resist the string both physically as well in terms of coil induction.

    Are you sure that the flux change the pole piece is really that significant? The gauss at the top of an AlNiCo pole piece is over 1000, but but the string itself only has a gauss of somewhere between 100 - 250 since it's some distance away from the pole piece, so then how much stronger is the additional flux in the permeable pole pieces going to be? Isn't the fact that the string has a magnetic polarity enough to induce voltage in the coil all by itself, without the need to consider the flux change within the permeable pole piece?

    I don't think I'd describe eddy currents as having a filtering effect, because filter implies a frequency cut off, like "low pass filter", where as increasing or decreasing the Q by way of eddy currents serves more to widen or narrow the resonant bandwidth.
     
    Last edited: Apr 30, 2016
  13. Zexcoil

    Zexcoil Vendor

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    I'm working on some blog posts that will clarify things.

    The thing to consider is that the magnetic field of the pickup doesn't matter, at least not nearly as much as you may think. In the presence of a magnetized string, a pickup with no magnet at all will generate the same signal level as a pickup with a magnet. The perspective I'm talking about is one of the pickup exclusively as a receiver of flux. This may be an oversimplification, but it does capture most of what's going on.

    I can demonstrate this experimentally. I can also quantify the eddy current effect and exactly how it affects the frequency response.

    And I do think a filter is the right way to think about it, pickups in general (or more correctly the RLC circuit composed of the pickup, controls, cable, etc.), really.
     
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  14. xmd5a

    xmd5a Member

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    I understand what you're saying, but you mentioned the permeability of the pole piece being important, and I guess I'm wondering why you'd place emphasis there.

    Steel poles are much more permeable than AlNiCo poles, and they have to be in order to magnetize the strings while having no permanent magnetism of their own, but that same permeability causes them to greatly increase the inductance, which swamps the significance of eddy currents. For example, a Strat pickup with AlNiCo pole pieces typically has 2.5H inductance, but a steel poled ceramic pickup has an inductance closer to 3.5H, dropping it's resonant peak by roughly 1kHz, which is nothing to sneeze at. I'm hard pressed to think of a scenario is which eddy current activity varies from one pole type to another, wherein the change in inductance is not more significant.

    But you had said that the wind count merely moves the peak around, that's part of the LCR equation too, so your statement is a bit of a contradiction. If we're talking LCR filters, you could count the eddy currents as being part of the "R", but the wind count constitutes the L and the C. It's just confusing to say that the pole piece is "filtering" when the filter was already there, the pole piece merely modifies it's behavior.
     
    Last edited: Apr 30, 2016
  15. DR5Guy

    DR5Guy Member

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    Interesting, I'd like to read your blog, once the results are ready. If this is correct, it could mean the pickups can come from the factory without magnets, provided a portion of the string is magnetized by the manufacturer.
     
  16. xmd5a

    xmd5a Member

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    As a matter of fact, there was an acoustic guitar pickup in the 80's called a "String Vision", and the pickup had no magnet, and instead you would magnetize the strings with a little hand held magnet. Supposedly the output was really low. I have no idea what the benefits were to such a design.
     
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