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Using Neodymium (ndfeb) Magnets In Pickups


Robert_the_damned
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Hi all,

I was wondering if neodymium magnets would be 'good' in electric guitar pickups. I know a few acoustic pickups use them and that they've been used quite a lot by the sustainer builders thread but are they advisable for regular guitar pickups? I ask as they seem to be the only readily available magnets arround at the moment (or at least so it seems to me, I've asked for magnet sources in a seperate thread).

I know they're very strong even compared to ceramics and so strong string pull might be a problem if to larger a magnet is used. Anyone got any advice?

Thanks

Robert

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The neodymiums are quite powerful, but expensive compared to other magnets when considered for a production environment. They're also brittle and corrode easily. They're great for use in microphones and acoustic mag pickups because you can use a really small, lightweight magnet and get the same performance as a large ceramic magnet.

String pull may be an issue only if you use a magnet that is too large or powerful in the design. You may also want to fully pot the pickup with either wax or epoxy to protect the magnet and wiring from corrosion, too.

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Neodymium magnets are really pretty cheap. The correct strength to get enough signal but avoid string pull can be determined by experimentation. If you use steel rod pole pieces you can put a small magnet on the back of each. Try different sizes for different compromises between sound and output level. I have gotten as much as about 4 volts peak to peak, but with so much string pull the two modes (horizontal and vertical) of the string vibration are shifted apart in frequency and beat against each other horrendously. So with little magnets about 1/8" deep and about the diameter of a polepiece, they sound really good and give the usual level. So there is not that much to gain except convenience in getting different sounds.

One more thing. You should not use neodymium magnets as the poles peices themselves; they are way too strong!

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I think they'd be most useful if you're building a guitar that needs a really thin pickup or something really lightweight--much like the Fishman Rare Earth pickups.

I'd rather use a sandwich-blade design instead of a polepiece design if I were using rare earth magnets. Spread out the field more evenly for less string pull.

Bill Lawrence doesn't use neodymium and goes to great length to explain why on his website. His brand-name pickups use either ceramic ferrite or Alnico. The Fender SCNs use Samarium Cobalt, which is almost as strong and efficient as neodymium, but better suited to a production environment.

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:D thanks for the advice guys. I've got a couple of cheepo humbuckers lieing arround so I'm going to have a play with some differant magnets when I get the chance to buy some. They're dirt cheep on UK ebay so I'll probably order some off there!

Mike your suggestion seems sensible. Maybe it would even be possible to 'bias' the pickup to be more sensitive to some strings over others by using slightly larger magnets on those strings? like a fender stagered pole piece arrangement but without the protruding poles?

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:D thanks for the advice guys. I've got a couple of cheepo humbuckers lieing arround so I'm going to have a play with some differant magnets when I get the chance to buy some. They're dirt cheep on UK ebay so I'll probably order some off there!

Mike your suggestion seems sensible. Maybe it would even be possible to 'bias' the pickup to be more sensitive to some strings over others by using slightly larger magnets on those strings? like a fender stagered pole piece arrangement but without the protruding poles?

Robert, that sounds like a good idea; I have not tried it. On the last pickup with Neodymium magnets that I made, I drilled and tapped the steel polepices and put in allen cap screws for adjustment.

Bill Lawrence has a lot of interesting things on his web site. Under "magnets", he says that it is not the type of magnet (alnico, cerramic, etc.) that matters, but rather how you use it. That is what I have found, too. I can see why Neodymium might be hard to work with in a production environment, although most of them are now sold with a nickel plating that makes them pretty convenient. I think they are ideal for making special one of a kind pickups of any size or for any use.

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Mike, that sounds like its most likely true, that its the field strength and shape that affects the sound rather than the 'magic tone factor' of the material.

Is Neodymium easy to work? I don't have access to any machine tools at home but my friend has just about everything you could want! Does it demagnatise at all if worked to hard? (I've heard that some magenets do that? is it true or scaremongering?)

I'll have to get some magnets and wind various differant coils and try them out....I could even do some rough magnetic field plots if my school will lend me their field strength detector. hmmm sounds like I have some physics teachers to perswade!

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Mike, that sounds like its most likely true, that its the field strength and shape that affects the sound rather than the 'magic tone factor' of the material.

Is Neodymium easy to work? I don't have access to any machine tools at home but my friend has just about everything you could want! Does it demagnatise at all if worked to hard? (I've heard that some magenets do that? is it true or scaremongering?)

I'll have to get some magnets and wind various differant coils and try them out....I could even do some rough magnetic field plots if my school will lend me their field strength detector. hmmm sounds like I have some physics teachers to perswade!

Robert

You should not try to cut or machine it, but rather just use the small magnets of various sizes that you can buy nickel plated and ready to pop onto a pole structure. Neodymium does not demagnetize easily except from heating, so just use it the way it comes.

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Robert,

I've got some new Alnico (I think) pole pieces at home. If you need them for your experiments then drop me a PM with your address and I'll put some in the post for you.

I've also got something called FEMM on my computer (Finite Elements of Magnetic...errr....something). SUpposed to be waht they use for desiging pickups. Not tried to work out hoe to use it yet but if you want it, I'll try to find the link.

Where in Essex are you, I've been shooting in and out of Colchester recently (where my bro was born and my dad was in nick, ahh the memories :D )

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Thanks for the advice Mike. :D I can see how machining would be bad due to the heat caused by the cutting/drill. How did you drill out your magnets then?

Robert,

I do not drill out the magnets, just use them as they are. They go on the end of the steel pole piece away from the string, one little magnet on each pole piece. I drilled out and tapped the steel pole pieces, and then used allen cap screws cut off so that were just a bit shorter than the pole piece, so they could not come through and hit the magnet.

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**slaps self** duh how stupid am I? I need to learn to read things properly I think! :D that sounds very sensible! Could you also use a nut glued to the pickup base to hold the screw pole pieces and then use a P90 or humbucker magnet configuration and have the magnet attached to the side of the nut?

That ought to work, have not done it myself. I have always assumed that it was better to use pole pieces with a larger diameter, more like the slugs used in standard humbuckers rather than the screws, but I do not really know. Your idea is a way to make a unique pickup without any machining. Sounds good.

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Hi there...

I've done a bit with Rare Earth magnets (search on rare earth maybe) and pickups and of course the sustainer. All the info and tutorial on FEMM was recently discussed on the Sustainer Thread.

As far as Neodynimium Magnets go...DO NOT TRY TO MACHINE OR CUT THESE THINGS>>>DANGER.

I'll explain why another time, but I am not kidding...

I do think there is a role for Neodyminium mags as Bill Lawrence has done with the new fender SCN pickups.

The appropriate size though for a pickup is very small and not what you tend to find in shops. I was using mags 3mmx2mm that had the same strength as a typical alnico fender pole!!!

If you want to emulate a traditional design, use traditional materials. The key to magnets in pickup design is not in the strength of the pickup but in the "shape" of the field. Neo mags are small and their fields are compact and powerful...is this what is required? Maybe...but you are looking at new designs for which there is a lot of scope.

If you are considering adding rare earth magnets to a pickup...beware, they will demagnetise your pickups ceramic or alnico poles.

Anyway...as I say...there is new stuff on the sustainer thread (back a few pages) on FEMM and always on RE mags. Do check out a recent thread on bill lawrence and check out his website on pickupology...there is way too much voodoo on pickup material qualities and "tone".

Just remember, the magnet is there to produce a magnetic field. A magnetic field is a magnetic field...but the material can influence the "shape" of this field and this is what is important...the magnetisim itself is simply that, magnetism (not ceramicism or alnicoism or neodyminiumism) the material is just a means to produce the field.

pete

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:D silly me searched for just about every name except 'rare earth' :D I'll be more through next time

I'll check out the FEMM tutorial, I've seen some models that have been done using it on skgutiar.com and was going to go have a look for it today! a tutorial will be very useful so I'll go find that too B)

There are tons of Neodymium magnets on the UK ebay all the time, in all maners of sizes, I think I really need to buy some and try.

I've heard of the 'demagnatising' properties so these things are not going to be kept in the same box as my spare (junk) pickups!

:D I'm going to try and make some models of current pickup designs on FEMM and then see if I can recreate these field shapes with differant magnets B) thanks for the help Pete

Robert

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:D hate to be replying to myself but I'd though I'd post up a picture :D make this thread look prettier.

pickups.JPG

Neodumium magnets on the left and a 'standard' double slug AlNiCo 5 humbucker on the right. B) couldn't have done them without your tutorial Pete!

The 'strings sensing' area seems to be nearly the same (slightly stronger on the Neodumium, but the field where the coils would be is a lot stronger, so maybe just less winds?

Robert

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Wow, that's cool...you really seem to have got the hang of FEMM...

Now you got to get a hang of what the permanent magnets do in an electromagnetic device!

Although it looks similar, it is not the same...most of the magnets field loops around itself there far before it gets anywhere near the strings for instance. But it is an interesting model as an example. We cant know from this what it would sound like, but for sure it would pickup vibrations in the magnetic field. Would it be more "powerful" for having neodyminium below the coil when the sensing field is similar? Would the pickups resonant qualities (electronic signiture, or "tone") be better?

Many many questions like this...just don't believe your own internal hype (mine too) that Rare Earth will be mystically better...err, 'cause it's rare right! No...but for sure you could do something radically different with something as small and powerfull as this....not just attempt to use them to create what you already have...

The sustainer project really overtook my "work" in pickup design that started it off. I too was fascinated, and a lot of the driver design is really just a reverse pickup with different qualities. If people are unfamiliar with some of the stuff that was going on in that, here is one of the hex drivers...

drvlighton1.jpg

This also works as a low impedance pickup of a radical design...if preamped. The design is secret but uses an idea that I had of a balanced magnetic field. There are two magnets of opposite poles for each string and the string vibrates between them. As the strings vibrate within their own "neutral" zone, it is sensing how close the string gets as it vibrates to it's north or south pole. It's too much too explain, and secret, but the point is that these little magnets can be used to create radical designs and unexpected outcomes. Here for instance is a pickup effectively...or more precisely six pickups, 12 magnets, a pickup cover, 5 LED's (that shine between the strings) and the whole thing fits in a package 5mm wide and 5mm deep!

This is just one of an infinite array of design options that arises from new materials. But these options may not be an improvement. A pickup is a sensor, a stronger magnetic field may actually dampen vibration resulting in a loss of harmonics and sustain...possibly even intonation! Consider EMG's or othere low impedance pickups..."power" is produced by pre-amplification (you can have as much power as you like if you put a battery in your guitar) and improved response is a result of lower magnetic strength.

OK...enough for now...it is fascinating stuff, and you have done some fine work with FEMM there. Use it to explore magnets, they are kind of amazing and this kind of thing makes the invisible, visible. It is only a model though, and remember...neither of us know enough about the effects to be able to judge what they will be on a moving string and a sensing coil in it, let alone whether it will be an improvement... pete

BTW...the above device is designed as a driver, which is very different in what it does to a pickup, though it works on the same principle. This was made to drive strings...it was not built for pickup "tone"...though it does work as a pickup (I did test it), there was nothing that would suggest that it is infact better in response...it was a lot smaller and effectively had little if any magnetic pull on the strings, amoungst other unique qualities... :D

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Hi Pete

Thanks a lot for your imput. I really appreciate it, you have a lot more experiance actually working with things like this I think!

The main reason I want to use the Rare Earth magnets is because at the current point in time I can buy 50 odd of the small 3mm cubed ones for less than the cost of one AlNiCo humbucker magnet! The possibilities of all the wonderful designs that can be done with such powerful magnets is more of a secondary intrest!

I recognise that driver I believe from somewhere in the sustainer thread! The idea of very low powered (magneticly speeking) low impedance pickups with a pre-amp is something that I have been considering. I'd like to get a functioning 'conventional' pickup up and working first. Then I'll start being inventive :D

I've got more ideas now that I can think about.....I need a lie down!

Robert

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Well I have know doubt you can get something out of the pickup...whatever it is you create! As long as there is a magnetic field going through the a coil <ahttp://www.projectguitar.com/uploads/emoticons/default_biggrin.png' alt=':D'> and I'm really pleased that you seem to have got the hang of FEMM so quick...for other's here is the link to that part of the sustainer thread with the FEMM link for anyone else...FEMM Stuff

For those who are attracted by pretty colours and want to see what typical fields around typical pickups look like...check out Steven Kirsten's FEMM diagrams...http://www.skguitar.com/

But do check out the Bill Lawrence articles to get some perspective on what goes into pickup design...Bill Lawrence Thread

and...Pickupology

have fun... pete

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If you look at the main site for FEMM, at the FAQs, you see that question 6 is important in showing the limitation of the accuracy of the field models predicted for some pickup magnet configurations. FEMM treats a permanent magnet as a source of magetic field, but does not allow its magnetic material to be modified by applied fields.

Here is a brief explanation of the significance:

A ferromagnetic material (iron steel, ferrites, some ceramics and rare earths, etc) has permeability, the ability to amplify an applied magnetic field.

A ferromagnetic material might also produce a permanent magnetic field.

Permanent magnets might have a low or high permeablity. The very strong magnets, neodymium, samarium colbalt, and some ceramics, have low permeabilties. All the little magnetic domains are pretty much flipped in the same direction and cannot be easily changed. That is why they are so strong. Alnico is a weaker magnet, but has a significant permeability.

FEMM is most accurate when the permeablity of the permanent magnetic material is low (generally a very strong magnet), and the permeabilty of the other magnetic material in the circuit (cores, etc.) is high. So Robert's left plot is probably more accurate than his right plot. The permeabilities of Alnico and the steel cores are similar, and so the effect of the magnet coupling the two pole pieces together is probably significant, but ignored in the plot. Probably the field lines are more closely confined to the cores than shown, and the field above the cores is a bit stronger.

Edited by Mike Sulzer
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mhmm that's intresting....I've done several more refined models (after I found out how to get the program working in milimeters so it was easy to put things in accurately!). I've modeled a large number of pickup designs and managed to duplicate most of them (and improve on some if I may say so myself!).

Have I correctly understood that FEMM basicly takes into account the 'conducted' magnetic field but ignores the 'induced' magnetic field a coupled non-perminant magnet? if so that might explain why I was wondering why fender type AlNiCo rod pickups had such powerful fields compared to humbuckers! or maybe they really do?!? :D

B) to much thinking and not enough guitar playing

:D oh btw has anyone ever taken appart an epiphone covered pickup? They certainly don't make 'em like they used to! They've gone for the horrid 'throw everything into the cover then pour wax on it and stick a base plate to it' route that I've seen in a lot of cheep single coils, even Encore make they're pickups in a more traditional way! (they're not better pickups though!). Oh well no matter what I do to it now it'll be firstly less muddy and secondly far less microphonic!

:D I have to admit to loveing my Epiphone Les Paul (not so)Standard, it will rock when I've made my P-90/ humbucker half breeds!

B) now back on topic

Robert

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Have I correctly understood that FEMM basicly takes into account the 'conducted' magnetic field but ignores the 'induced' magnetic field a coupled non-perminant magnet? if so that might explain why I was wondering why fender type AlNiCo rod pickups had such powerful fields compared to humbuckers! or maybe they really do?!? :D

Robert

It corrrectly computes the field in the situation where the magnetization in the permanents would not change significantly, that is, when the permeabilty of the permanent magnets is low, or when the permanent magnets are not very near the other magnetic material. This is a somewhat tricky concept, and I am sorry if it is not clear! I have been an engineer for many years, and I still find magnetic circuits difficult to understand.

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I think I understand.

I agree magnatism is a very hard thing to get the hang of. I'm nearing the end of A-level physics and although we've been shown that a wire cutting field lines causes a current in the wire the teachers seem reluctant to say *why* it does so. Its hard to grasp whats going on especially as you can't 'see' the magnetic fields, which is one reason that FEMM is so useful!

:D thanks for the explenations

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