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Thread: Self-demagnetizing & Jazzmaster pickups

  1. #1
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    Self-demagnetizing & Jazzmaster pickups

    Folks -

    So, those Alnico rods on those pickups don't appear to follow the usual recommended aspect ratio for this material. Come to think of it, I haven't actually measured any but somehow an image persists in my mind of shorter-than-supposedly-ideal little rods.

    If so, do we think there's been a significant drop in gauss level over the decades in some of the older units (or has someone measured such things?)

    In any case, I'd like to start getting an idea of how much flux seems "ideal" for given string-to-polepiece distances for given string gauges in this design.

    I also have a vague recollection that one of you wiser guys once said that Leo never lost any sleep over stuff like this, which is doubtless true.

    Bob Palmieri

  2. #2
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    I'm pretty sure that JM pups use 0.471" * 0.187" A5 rods.
    fieldwrangler likes this.

  3. #3
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    as far as typical alnico rods go the shorter the rod the weaker the magnet, once you get sown to 3/16 by 1/4 long you have a magnet that will hardly lift its own weight, dont know if the length makes it more likely to discharge over time being in proximity to like poles
    fieldwrangler likes this.

  4. #4
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    Quote Originally Posted by Lollar Jason View Post
    as far as typical alnico rods go the shorter the rod the weaker the magnet, once you get sown to 3/16 by 1/4 long you have a magnet that will hardly lift its own weight, dont know if the length makes it more likely to discharge over time being in proximity to like poles
    Jason -

    Yup, thanks for this. Just poked around to find the very general rule of thumb for Alnico (I recall this ratio being dependant on the grade of Alnico) but here we have it:

    Alnico is better at resisting self demagnetisation by being longer in the direction of magnetisation than in the dimensions of the pole face (usually termed Length to Diameter, L/D, ratio). A higher L/D ratio increases the working point on the Intrinsic curve. This is why Alnico magnets are very rarely short in length (they are often seen in bar, rod or horseshoe shapes) and a L/D ration of at least 4:1 is ideally required to get good performance from an Alnico magnet or an Alnico magnetic assembly (having Alnico is a ferromagnetic assembly and magnetising in-situ boosts the L/D ratio of Alnico creating a higher magnetic output). If the design is correct with Alnico, it can outperform many magnets at ambient temperature and all other magnets at high temperatures. To get the most out of an Alnico magnet, the entire magnetic circuit (magnet, ferrous parts nearby, external magnetic fields, etc) needs to be considered.

    The last part definitely drives home your point about being close to those other rods.

    Bob Palmieri

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