Magnetizer/Demagnetizer

[tbryanh]

I would like to make a unit(s) to magnetize and demagnetize alnico pickup slugs.

To demagnetize, I have thought of using a motor stator, say a 1/2 hp motor with the stator removed.

To magnetize, it appears that high current DC pulses are needed. I have DIY plans for a magneto magnetizer "How to Build a Magneto Magnetizer" David, J. Gingery http://www.lindsaybks.com/dgjp/djgbk/magneto/index.html

The plans look good, and I am sure the unit would magnetize the alnico slugs to their maximum strength. The thing is, I want to experiment with magnetizing the slugs to less than their maximum strenght. I have heard that this is part of what puts the "vintage" sound in old pickups. Apparently alnico slugs lose some of their strenght as time passes. This apparently gives pickups a mellower sound.

I suppose I could use a variac on the magneto magnetizer to control the peak of the current pulses, but I was thinkging that I could use smooth DC instead from one of my DC power supplies instead. Since rare earth magnets can be used to magnetize alnico slugs, and rare earth magnets have steady magnetic fields, smooth DC should work.

Any helpful comments or suggestions will be much appreciated.

[OFM]

Neodymium magnets are a very simple and affordable tool to demagnetize Alnico magnets.

By the way, i've read from Bill Lawrence "Pickupology" that "Aged magnets" were just a myth, since Alnico magnets doesn't lose more than 0,01% of their magnetism in 50 years.

(and vintage guitars sounded great when they were built, too)

[tbryanh]

Please explain how to demagnetize with neodymium. I am under the impression that you need an alternating magnetic field from an AC current going through a coil of wire.

My understanding is that magnets in pickups do lose some strength over time. This happens when some of the micromagnets inside the magnet come out of alignment. Vibrations and alternating magnetic fields can cause the misalignments to occur. Guitars are set to rest on amplifiers during breaks, and the alternating magnetic field in the power supply transformer of the amp causes some of the micromagnets to come out of alignment. And the vibrations in the body of the guitar from the strings and the feedback from the amp also causes some of the micromagnets to come out of alignment.

I am sure this affects tone. There are various alnico's, 1, 2, 3, etc., and they have different strengths when fully magnetized, and they cause different tones when installed in the same pickup.

Thanks

[corduroyew]

To demagnatize an alnico magnet, just wave the like pole of the neo mag over it. You won't be able to get the magnet to exactly 0 gauss this way, but you can lower or even revers the magnetic pull and it'll take less time than putting a pickup into your machine.

[Spence]

Neodymium magnets are a very simple and affordable tool to demagnetize Alnico magnets.

By the way, i've read from Bill Lawrence "Pickupology" that "Aged magnets" were just a myth, since Alnico magnets doesn't lose more than 0,01% of their magnetism in 50 years.

(and vintage guitars sounded great when they were built, too)

Bill Lawrence talks a load of rubbish.

AlNiCo magnets only lose 0.01% in 50 years in an environment devoid of any external influence.

So it's not a myth.

Back last year I took part in a vintage Strat shootout for a guitar magazine.
We compared a 1957, a 1959, two 1962's and a 1963 Strat. My main role was to look into the pickups of each guitar and work out their gauss relation to the tone.

OK, so one guitar was ash with a maple neck, two were alder with slab rosewood necks, one was alder with a rosewood veneer neck and the other was ash with a slab rosewood board.

But the key points in relation to your question is this:

All the guitars had suffered quite a serious drop in gauss levels except for the 1957 guitar which had been in storage for most of it's life. It's gauss levels had hardly dropped. The 1957 guitar was very harsh sounding compared to all the others. I hated it. There is something about degaussed strat pickups.

So, in the real world, perhaps you shouldn't take any notice of Willi Lorenz Stich who after all isn't quite what he seems.

[corduroyew]

You also have to keep in mind that Fender magnetized their early pickups with a magnetizer built from a car battery. This meant that some pickups got more charge than others depending on how strong the battery was. They were not too careful storing charged magnets either. Even the way you pull a charged alnico magnet off of a block of magnets can change the charge of the magnet.

[David Schwab]

To magnetize, it appears that high current DC pulses are needed. I have DIY plans for a magneto magnetizer "How to Build a Magneto Magnetizer" David, J. Gingery http://www.lindsaybks.com/dgjp/djgbk/magneto/index.html

The plans look good, and I am sure the unit would magnetize the alnico slugs to their maximum strength.

It states right on that page:

This will not recharge newer alnico, samarium, and similar alloy magnets since these need an enormous magnetic impulse beyond the capabilities of this machine. And beside these newer magnets usually don't go "dead" like "plain" ones.

[truetone]

I've tested my 62' strat pickups and they read the maximum 25 gauss. I would of thought they would be weaker too, but amazingly they weren't

[Zhangliqun]

Just two neo magnets in a vice, opposite poles facing each other about 2" apart will do fine for fully charging magnets. For degaussing you might want to have them a good deal farther apart than that because they are so strong that they will reverse the polarity of the magnet.

So I just use an Alnico 8 magnet for degaussing.

[devnull]

How big should the Neos be?

Just two neo magnets in a vice, opposite poles facing each other about 2" apart will do fine for fully charging magnets. For degaussing you might want to have them a good deal farther apart than that because they are so strong that they will reverse the polarity of the magnet.

So I just use an Alnico 8 magnet for degaussing.

How big should those neos be? I'm pricing them and they can get kind of expensive.

[Possum]

...

There is no such thing as magnets that measure 25 "gauss." If they measured that low they'd be dead. MAGNETOMERS do NOT measure GAUSS. They measure stength on a spring scale, sorry. Seymour Duncan uses one of those things and they I guess are useful for relative measurements, but scientifically accurate they're not. A full charged D or G pole magnet measure about 1200 guass :-)

Full charged magnets are not really vintage in the way most think of it. Gibson for example bought magnets already charged, and we all know that if you buy charged magnets they aren't really holding a full charge once you put them in a pickup. Leo Fender on the other hand, DID have a charger and charged them full (or did he really). But 50 years of guitars being stood up against powerful speaker cabs, being banged around, and exposed to magnetic fields etc. and possibly maybe not even really charged bang full at the factory, they just don't have a full charge that they can hold.

Spence is right. All the old Fender stuff I've looked over has lost a fair amount of charge, except the real nocaster pickup I have, but the baseplate protects the charge, still its not a full charge it could hold. The Gibson magnets I've measured hold about 500-600 guass versus the 700+ they will hold when newly charged.

Neos work good but for a full charge you need one thats scary strong. I got some 2x4 block neos, two of them that are so strong, they came attached to eachother with a block of wood in between, I never had the courage to try to pull them apart. If they bang together they can explode in a nasty way. But they will fully charge alnico from one end anyway, an uneven charge coming from one side. Having a real coil magnet charger is great but not totally necessery, I got by for years with the neo and no worries. I do love my Magnetool charger though. And yes, degaussing to vintage levels all you do is push a ceramic magnet against the alnico a bit and you're done, but you need a real guassmeter to see whats happening.

[David Schwab]

I got some 2x4 block neos, two of them that are so strong, they came attached to eachother with a block of wood in between, I never had the courage to try to pull them apart.

If you stick one of them to a big steel vice, and then bring the other jaw up to the other one, you should be able to open the vice and separate them. Once they are stuck on the vice, you can bring them quite close together and they wont jump off the vice.

At least it works with the smaller magnets I use with a drill press vice, and they are still really strong. I've broken quite a few of them when they came crashing together!

[Zhangliqun]

The neo's Stewmac sells seem to do the trick for me.

[Possum]

....

I tried the StewMac round neos just for fun, they don't fully charge alnico, which is probably a good thing maybe, but in some cases you want a full charge and they are too weak.....

[EFK]

I;ve noticed that when using big neos for charging the gauss readings taken along the pole (edge on bar magnets) are pretty constantly variable, usually strongest along the corner edge of the last portion of the bar magnet pulled away from the neo. Now, something which I've wondered about but have not been able to test in theory (b/c I don;t have big piles of same-grade bar mags) is this: if one were to charge up with neos say 30 to 40 (or more) A5 (or A4, 3 etc.) bar mags, then stick them all together in a big brick, I would imagine they may slightly degauss - at least those with the strongest charges - but would their charges 'even-out' somewhat? I be very curious to hear from anyone who has experience with this.