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Degaussing, or "aging" AlNiCo pole pieces

Discussion in 'Just Pickups' started by Antigua Tele, Feb 17, 2018.

  1. Antigua Tele

    Antigua Tele Friend of Leo's

    Jun 2, 2014
    west coast
    Have you heard about pickup makers boasting "partially degaussed" AlNiCo for a more vintage tone? Well it's easy to do at home, and if the AlNiCo pole pieces are exposed, you don't even have to take the pickups out of the guitar to proceed.


    Why do this? The AlNiCo magnet is not a dead technology, though this type of magnet has been increasingly usurped by ceramic and rare earth magnets, which avoid several disadvantages associated with AlNiCo.

    One major disadvantage of AlNiCo is that physical shock, extreme heat changes, and exposure to stray magnetic fields can cause it to lose residual flux, or "strength". In the context of guitar pickups that contain AlNiCo magnets, degaussed magnets are valued by guitarists for either sounding "aged", or "mellow", or what have you.

    The effect of degaussing pole pieces is very similar to simply lowering pickups, so if you want to see if you will like the sound before hand, you can try simply lowering the pickups by three or four millimeters and then observing the difference. The advantage to degaussing the pole pieces as opposed to simply lowering the pickups is mostly in the fact that the pickups will not appear lowered by three or four millimeters. You can also degauss specific pole pieces, to make some of them produce a "lowered" sound, and others a "raised" sound.

    A fun thing to try is to degauss some pole pieces while leaving others full strength. The result could be similar to a Seymour Duncan "Five Two", where there are stronger AlNiCo 5 pole pieces under the wound string, and weaker AlNiCo 2 below the plain strings. I just gave this a try with my own Strat and the result is as you'd expect, the plain string sound mellowed out.


    How do you do it? Degaussing AlNiCo on purpose can be a little difficult, because you have to expose it to a magnetic field that is not so strong that re-polarizes the AlNiCo, nor so weak that it fails to weaken the AlNiCo at all, but there is a way to reliably degauss AlNiCo pole pieces to a very useful degree, and that is by using a standard AlNiCo 5 pole piece as the degaussing agent.

    The trick is to take the pickup you want to partially degauss, then simply press a fully charged AlNiCo 5 pole piece into the tops of the pole pieces you want to degauss, so that they're "face against face", and trying to push away. Hold them in direct contact for about three to five seconds, then lift it away. This will reduce the flux density of an AlNiCo 5 pole piece by nearly half, or cut the flux density of AlNiCo 2, 3 or 4 by about 25%. AlNiCo pole pieces come in different lengths for staggered Strotcaster pickups, but as long as it's over 15mm in length, it will be strong enough to get the job done. I've found that holding the pole piece for a longer period of time, like twenty seconds, will further reduce the gauss another 10% to 15%, after which point there is no further change.

    Since both the target pole piece, and the "agent" pole piece you use for degaussing will mutually lose flux density, you'll have to recharge the "agent" pole piece using a neodymium magnet, for each pole piece that you degauss. It's very helpful to have a compass or a polarity tester on hand in order to know the polarity of the pickup and the other magnets, rather than simply noting whether they attract or repel.

    Technically, you don't even need a standalone pole piece to act as the "agent", you could use another AlNiCo 5 pickup with exposed pole pieces, then touch the two pickup's pole piece's faces together , which would degauss both pickups at the same time.


    How does it work? The key ingredient is that the "H field" of the AlNiCo 5 pole piece is just strong enough, and the coercivity of AlNiCo low enough, that it will partially degauss other AlNiCo pole pieces. Unless you have a magnetometer, you won't know exactly where you started and where you end up, but you can use a small screw or a paperclip and gauge how much the magnetic attraction of the pole piece has changed. A fully charged AlNiCo pole piece will hold a paperclip rather tightly, where as a 50% degaussed AlNiCo 5 won't put up much of a fight. AlNiCo 2, 3 and 4 only produce about 50% of the flux density of AlNico 5 when fully charged, so this technique doesn't work as well with those alloys. A cheap analogue Annis magnetometer costs about $80 on eBay, while a better, digital "Hall Effect" magnetometer can be found for as little as $100, if you're willing to make a small investment.

    Note that if you only degauss the top of the pole piece, the strength at the bottom side will still be nearly full strength. Degaussing both the top and the bottom reduce the flux density at the top side by about another 50G.


    How much difference does it make? In my testing, which is pictured below, a fully charged AlNiCo 5 pole piece reduced the charge of other AlNiCo 5 pole pieces from around 1050 guass down to about 650 gauss. You might think half the magnetic strength means half the volume, but it doesn't work out that way. In fact, you have to degauss the pole piece by about this much in order to perceive a noticeable difference. Due to the instability of AlNiCo, some AlNiCo 5 pickups are received after having lost 20% of their charge through one mechanism or another, but with that small degree of loss, few people, if any, even notice. AlNiCo 3 pole pieces produce about 650 gauss at the pole tops when fully charged, while AlNiCo 2 and 4 are not much stronger. When running your guitar squeaky clean, you can perceive a bit of a volume drop, but with almost any amount of gain, the volume difference disappears, while the "softer" tonal qualities of degaussed pole pieces seems to remain.

    Supposing you have a pickup with AlNiCo 2, 3, or 4 pole pieces, I've found that if you try to degauss AlNiCo 2 with another AlNiCo 2 pole piece, you won't get much of a reduction in gauss. Starting out at 700G, an AlNiCo 2 pole pieces dropped to about 650G, not much of a difference. On the other hand, placing an AlNiCo 5 pole piece face against face to the AlNiCo 2 pole piece reduced it's strength from 700G down to 550G. Since AlNiCo 3 and 4 have a coercivity that is very close to that of AlNiCo 2, it's likely you would get similar results with those alloys.


    How do I undo this if I don't like it? In order to restore a pickup to stock condition, or to freshly charge a pole piece for this purpose, you'd want to get a neodymium magnet. Neodymium is so strong that even a small magnet as is seen in the pictures below will almost fully charge AlNiCo pole pieces, though you'd want to get one that is a bit wider and longer in order to fully charge and a pickup, or bar magnet along it's entire face at one time. If the neodyium is especially large and strong, like strong enough to crush your fingers, then it will be strong enough to charge the pickup without even making contact with the pole pieces, and so you can just waive it over the top of the pickup.

    You will definitely need a compass, or a polarity tester, in order to make sure that you recharge the AlNiCo pole pieces with the same polar orientation they started out with, in order to maintain the correct phase for the pickup. Incidentally, any pickup can be made into an RW/RP pickup by deliberately reversing the magnetic polarity, and then reversing the lead wires (the coil does not have to actually be "reverse wound").

    In the case of a Telecaster neck pickup, you can degauss the pole pieces from the underside, but the AlNiCo will still be nearly full strength on the top side.


    Is there a downside? A caveat to doing this is that partially charged AlNiCo is always less stable than fully charged AlNiCo, so one you've reduced the flux density, the magnets will more easily lose charge over time, and it might become necessary to recharge the pole pieces to full strength again using a neodymium magnet, though you can partially degauss them once again, using the same technique described here.

    Also note that because AlNiCo 8 has a higher coercivity than lower AlNiCo grades, this procedure would probably bot degauss it to a useful degree, if at all.


    Pictures:

    Charging up an AlNiCo 5 pole piece to be used to degauss other pole pieces:

    [​IMG]


    The freshly charged AnNiCo 5 pole piece measures about 1250G:

    [​IMG]


    Unadulterated SSL-1 reading ~1050G:

    [​IMG]


    Pressing the AlNiCo 5 pole piece into the SSL-1's pole pieces:

    [​IMG]


    The SSL-1 now measures about 650G at the pole top.

    [​IMG]






    Here is a pickup with AlNiCo 2 pole pieces, measuring ~700G

    [​IMG]


    After pressing the AlNiCo 2 pole piece to the AlNiCo 2 pole pieces within the pickup, the overall drop is barely 50 gauss.

    [​IMG]


    However, recharging the AlNiCo 2 pickup, and then pressing the AlNiCo 5 pole pieces against the AlNiCo 2 pole pieces caused them to drop to about 550 gauss:

    [​IMG]
     
    kingvox, 2blue2, Iago and 8 others like this.
  2. Bristlehound

    Bristlehound Tele-Afflicted

    Age:
    58
    Jan 4, 2017
    Wales
    mmm - so if one had a set of vintage stagger p/ups could one do this to just the G pole and therefore get a more even balance, or is this a bit simplistic?
     
  3. Antoon

    Antoon Tele-Holic

    775
    Feb 10, 2010
    Low Lands
    Great info! Thanks!
     
  4. Teleterr

    Teleterr Friend of Leo's

    Feb 7, 2011
    Lewes De.
    All those magnetic loss is myth threads had me convinced; and now your saying the opposite. Have you measured many old p-ups to see how widespread it is ?
     
  5. Antigua Tele

    Antigua Tele Friend of Leo's

    Jun 2, 2014
    west coast
    That's accurate, in fact I tried that and it worked as expected.
     
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  6. Antigua Tele

    Antigua Tele Friend of Leo's

    Jun 2, 2014
    west coast
    I don't know what claims were being made about vintage pickups and degaussed pole pieces, but it's a well known and accepted fact that AlNiCo easily loses residual flux through a number of means, such as physics shock, heat changes and stray magnetic fields. The reason is, in part because AlNiCo has a relatively low coercivity, which means that it's easy to magnetize and demagnetize in general. So while not all vintage pickups probably lost their charge, it's possible that many of them have, especially if the guitar has been moving around a lot.

    If anyone claimed this was the reason vintage instruments sound better, it's probably not the case that every AlNiCo pickup from the 50's degaussed by a noticeable amount, maybe not even most.

    That being said, there's a ton of evidence that guitarists prefer a weaker magnetic field to a stronger one, such as the varied opinion on pickup height settings, and the popularity of pickup which use AlNiCo 2 or 3 in place of AlNiCo 5.
     
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  7. ebb soul

    ebb soul Poster Extraordinaire

    Age:
    58
    Jun 7, 2016
    Smyrna georgia
    Stray magnetic feilds abound. I never understood how something can abound and be a,myth at, the same time.
     
  8. Steve Holt

    Steve Holt Tele-Holic

    938
    May 29, 2016
    Kansas
    So If I was making some strat pickups and went with alnico 2 for the neck and alnico 5 in the middle and bridge, and used your method to degauss the alnico 5 pole pieces, would it balance well with the alnico 2 that hasn't been degaussed? Or should I try to degauss the alnico 2 as well? I may or may not be short of a magnometer by the time I do this, I haven't decided if I want to invest in one, but I'm very interested in your post and would like to try it out with my own ears.
     
  9. BorderRadio

    BorderRadio Poster Extraordinaire Silver Supporter

    Apr 2, 2014
    Phoenix, AZ
    I need one of those little gauss meters.
     
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  10. Antigua Tele

    Antigua Tele Friend of Leo's

    Jun 2, 2014
    west coast
    BorderRadio likes this.
  11. Antigua Tele

    Antigua Tele Friend of Leo's

    Jun 2, 2014
    west coast
    For the most part, degaussed AlNiCo 5 that is brought down to ~600G is equivalent to AlNiCo 2, so you'd leave the AlNiCo 2 full strength if you were trying to balance them.

    What keeps the two from being perfectly identical is that AlNiCo 2/3/4 have a higher permeability than AlNiCo 5, which means they magnetize more readily than AlNiCo 5. Since voltage output is a result of magnetic change, that fact that AlNiCo 2/3/4 support a higher magnetic change, as the guitar string comes and goes, means they contribute to a greater voltage output, but the difference in practical testing was less than 1dBV, which means it's non audible.
     
  12. BorderRadio

    BorderRadio Poster Extraordinaire Silver Supporter

    Apr 2, 2014
    Phoenix, AZ
  13. bsman

    bsman Tele-Afflicted

    Jun 8, 2003
    Santa Clara
    So, you're saying that if the whole X-man evil genius thing doesn't work out this guy could make his living as a pickup tech?

    [​IMG]
     
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  14. Antigua Tele

    Antigua Tele Friend of Leo's

    Jun 2, 2014
    west coast
    I just conducted an experiment where I measured the flux density by distance. This test is very precise. I attached the probe and the AlNiCo pole pieces to the fingers of a Mitutoyo digital caliper, so the distance is accurate to within 0.01mm. The Gauss or teslameter is a WT10A.

    [​IMG]


    The reason I'm calling attention to it in this thread is there is an open question as to whether a degaussed AlNiCo 5 pole piece performs like AlNiCo 2, 3 and 4. As can be seen, the AlNiCo 2, 4 and degaussed AlNiCo 5 nearly overlap.

    It also appears that a slightly weaker AlNiCo 3 and a much stronger AlNiCo 5 pole piece follow the same curve, despite differences in flux density. According to the math of Kirk T McDonald , the flux density itself doesn't contribute to distortions / harmonics, just the fact of the magnetic field being non linear. Since these curves all match up very closely, it goes to show that the different magnet grades result in the same pattern of non linearity as one another.


    This model says that all magnetic pole pieces should sound the same, with stronger magnets simply producing more output, but what the model doesn't account for is difference in magnetic pull upon the guitar string, which is the sort of thing that causes "Stratitus", but also changes the harmonic amplitudes, but in a physical manner rather than an electrical one. By process of elimination, this strongly suggests that it is "string pull" that really sets magnets apart, and of course "string pull" comes down to magnetic strength, and so if you degauss an AlNiCo 5 pole piece such that it has similar strength to an AlNiCo 2 pole piece, it should perform the same.

    A caveat is that the lower AlNiCos 2, 3 and 4 have a higher permeability than AlNiCo 5, so when a pickup uses these for it's pole piece, it does have a higher inductance (by about 200 to 300mH) but this sort of difference can also be had by adding more turns of wire on the coil. So even though degaussing an AlNiCo 5 pole piece might make it perform like AlNiCo 2, 3 or 4, the AlNiCo 5 pickup will still be left with the same indutance and resonant peak that it had to begin with.
     
  15. Barncaster

    Barncaster Doctor of Teleocity

    This is a HUGE topic. I've done a lot of winding, gauss setting on magnets and critical listening and am always amazed at how different Alnico grades sound when charged to equivalent strengths. One of the best models is the PAF as magnets are easily swapped. Using the same guitar, amp, pup height, gauss level, etc, the Alnico formulations have consistent and distinct affects on how pickups sound. Physics is pretty cool.
     
    2blue2 likes this.
  16. E5RSY

    E5RSY Poster Extraordinaire

    Age:
    51
    Mar 5, 2009
    Georgetown, TX
    Yes, have heard it. But it doesn't make any sense to me since when the "vintage" recordings were made way back then the magnets in the pickups of the day were relatively young and not degaussed. They were effectively "new" pickups. So, how can degaussed be described as "vintage"?
     
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  17. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    61
    Jul 18, 2010
    Western Connecticut
    Me too. I'm thinking about how many times my pickups have been in close proximity on the shelf, or in the drawer...


    On another note, Jerry Garcia regularly replaced his pickups after a few years, feeling that they weakened over time. Guess he didn't like 'vintage tone'.
     
  18. TeleTucson

    TeleTucson Tele-Afflicted Ad Free Member

    Aug 6, 2016
    Tucson, AZ
    You'll have to ask Marty McFly for his first hand impression.
     
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  19. KyAnne

    KyAnne Tele-Afflicted

    As some great sage once said......."just play the damn thing".
    Who GAS about magnets? If you don't like your p.u. CHANGE it! Too much hassle messin' around with such B.S.. YMMV. Love, Kyanne
     
    E5RSY likes this.
  20. Antigua Tele

    Antigua Tele Friend of Leo's

    Jun 2, 2014
    west coast
    I don't see any reason to believe there is a substantial difference between magnetic strength and pickup height. It's true that different grades of AlNiCo feature different permeability and resistivity, which impacts the inductance and the resonant Q ever so slightly, but in all the ways that are important, I don't think it's really at all different from raising and lowering the pickups. I know that's extremely contrary to what all is claimed about how various AlNiCo grades effect the tone, but that's all they are, claims.
     
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