Pickup surrounds with different magnetic properties

Discussion in 'Luthier's Guitar & Bass Technical Discussion' started by Tony Done, Oct 9, 2019.

  1. Tony Done

    Tony Done Member

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    I'm wondering if anyone has experimented with, or has any info on the effect of pickup surrounds with different magnetic properties? The trad tele bridge pickup, and old Valco lap steel pickups got me thinking about this, being surrounded by ferromagnetic steel. OTOH, copper, lead and zinc are diamagnetic, while aluminium is paramagnetic, and these might have different effects on pickup tone. For example, is there any good evidence that using copper shielding on a pickguard affects the tone? How about aluminium?

    EDIT I might try the experimental approach on this.
     
    Last edited: Oct 9, 2019
  2. walterw

    walterw Gold Supporting Member

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    hmm!

    the claw around jaguar pickups is doing something, i think it's steel. steel or iron in the mix (i think) increases the inductance, which i'm given to understand makes for a louder pickup. the steel plate under a tele pickup certainly increases the punch.
    what's the diff? don't know those terms, and i thought copper and aluminum were kinda close in their electromagnetic behavior; they're both right up there at the top of the charts for conductivity.
    anodized aluminum pickguards certainly affect the sound, imparting a little zing and microphonics. dunno that a little shielding foil stuck to the bottom of a plastic pickguard affects all that much. (got me curious about the old-school fender aluminum shielding plates that went under those plastic pickguards though)
     
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  3. Tony Done

    Tony Done Member

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    Thanks Walter, that's a start.

    You mention Jag pickups. As an aside, I've been wondering if the reported tonal differencse (see Antigua Tele's work in TDPRI) between brass and nickel silver pickups are related to differences in magnetic properties, but so far I haven't been able to find anything about these alloys.
     
  4. walterw

    walterw Gold Supporting Member

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    i thought we talked about this!

    if you're referring to pickup covers then it's all about eddy currents; if the cover is "too conductive" like brass you get eddy currents that block the signal and dull the sound of the pickup. nickel silver (or "german silver" or whatever) is an alloy that's not quite as conductive, it does its job of shielding without significantly dulling the tone.

    traditional PAF covers are nickel silver because it doesn't attenuate treble, while traditional tele neck pickup covers are brass because it does.

    neither material is magnetic
     
  5. Tony Done

    Tony Done Member

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    You're right, but I'm wondering if there is more to it than eddy currents, based on the data for the elements involved, and if and/or the eddy current effects are related to differences in magnetic properties rather than simple differences in conductivity, for example. This will give you some idea of where I'm coming from, but I've only just scratched the surface:

    https://periodictable.com/Properties/A/MagneticType.html

    We didn't go this deeply into it in high school physics. :)
     
  6. walterw

    walterw Gold Supporting Member

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  7. Tony Done

    Tony Done Member

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    That all makes sense, and I'm not arguing with any of it, but I'm still wondering if/how it might be related to magnetic properties as well. Electric and magnetic effects are related.
     
  8. Timtam

    Timtam Member

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    GITEC are progressively publishing their analysis of original WRHBs and the Fender reissues, as well as clones ....
    https://www.gitec-forum-eng.de/2019...bout-the-fender-wide-range-humbucking-pickup/

    In addition to all the known differences between the CuNuFe pole originals and the bar magnet reissues, one that I hadn't heard before is the more magnetic covers on the reissues compared to the originals. The authors suggest that this is partly responsible for the microphonics of the reissues, for which they are heavily wax-potted (the originals are not).
    "Helmuth Lemme found the covers of the two original Fender Humbucking pickups to be completely nonmagnetic and thin enough to minimize eddy-currents. Chrome plating gives the pickups a nice shiny finish that has held up well over the decades. Although not potted with wax, the original Fender pickups feature very low susceptibility to microphonics - probably due to the non-magnetic cover.
    ...
    The cover of the Reissue is quite magnetic, interacting with the magnet and therefore prone to microphonics. Consequently, the potting is important and highly required."

    Full frequency comparisons are included. But given the totally different construction, it is hard to attribute measured differences accurately to specific individual construction differences.
     
    Last edited: Oct 10, 2019

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