alnico magnets: cast vs sintered

Discussion in 'Pickups & Electronics [BG]' started by #include <MK>, Jan 2, 2006.

  1. I'm interested in winding my own pickups and am wondering what people's thoughts and experiences are with cast and sintered alnico magnets. As far as I know, the sintered variety

    - are created by compressing metal and heating it till fusion occurs
    - don't influence the sound since they have no contact with the coil
    - have magnetism channeled by steel bars that influence the behaviour of the coil
    - cannot retain magnetism on its own

    I've read that Fender uses cast alnico magnets and that they have a higher resistance than sintered (see for details on the above). I've also read that sintered magnets don't retain their magnetism on their own. Do alnico magnets retain magnetism longer than the sintered variety?

    Also, how important is it that the magnets are transported unmagnetised? I supposed that strong magnetic fields can demagnetise them. In saying this, is there a limit as to the number of times a cast alnico magnet can be remagnetised. Also, as a matter of interest looking at the Seymour Duncan site

    what is the process of remagnetising and calibrating pickups or magnets? What tools, other than a guass meter, are required?
  2. Here's some additional information I recieved about the differences:

    Sintered alnico magnets
    - Manufactured from magnetic powder, then forged through compression
    - Magnets are sintered in a protective atmosphere (eg. vacuum) to give them demanding technological and mechanical characteristics
    - Lower measure of properties (eg. remenance, coercivity, intrinsic coercivity, maximum energy) than cast. Lower resistance than cast

    Cast alnico magnets
    - Original method for manufacturing alnico magnets
    - Alnico magnetic alloys with precisely defined chemical structures are cast in electric inductive smelting kilns. These alloys are cast in sand moulds, made through the Cronning method, at a temperature of about 1,600 C
    - Higher measure of properties (eg. remenance, coercivity, intrinsic coercivity, maximum energy) than sintered. Higher resistance than sintered

    This information was provided by a manufacturer of alnico magnets to a distributer who then sent me the information upon request.

    Still some questions though:

    - Is there a limit as to the number of times a cast alnico magnet can be remagnetised?
    - What is the process of remagnetising and calibrating pickups or magnets?
    - What tools, other than a guass meter, are required for remagnetising magnets?
  3. TheAmpNerd


    Apr 25, 2004
    Dallas, Texas
    I don't have answers to any of your questions.

    It is thought provoking though. I've read that alnico magnets
    become weaker after a year. This was also noticed by some
    guy named Jerry Garcia who replaced the alnico pickups in
    his axe yearly because they lost something.

    Good luck. : )
  4. luknfur


    Jan 14, 2004

    For the most part, those are really questions for people who actually make pups not people who use them - which is about 99% of the guys that frequent this forum. Maybe a dozen guys on TB have tinkered with winding with a few still active. Moohous (sp?) being the latest start up I'm aware of. Aside from some well known established makers (like Carey Norsdtrand, Rick Turner, etc. who are TB members but don't frequent often and I'd speculate unlikely up for taking the time to answer your questions) the most knowledgeable TB'r for winding pup I'm aware of is DavidRavenMoon. I'm guessing David would take the time - at least given some time.

    You could try emailing/PM'ing Carey, Rick, and the like with a brief message stating something like you've got x number of questions about alnico mags you'd appreciate them taking the time to answer but you understand if their too busy (whatever). Basically something brief, simple, respectful, and unimposing.

    These guys are really on another plain, have better things to do, and I'm guessing not their favorite thing to do even when they're making money off the inquirer let alone when not. If nothing else, these guys know that every answer is likely to generate more questions and therefore encourage more inquiry/further imposition. But it's not like there a tons of alternatives for this information - at least as it pertains to pickups.

    You can probably find some of your answers from an internet search regarding the magnets themselves unrelated to anything about pickups. There's a lot of engineering information about magnets online. Probably your best source would be a major local University Engineering program. You can talk directly to them, they have the time, they have the knowledge, and they're used to teaching. No doubt they'd be some unpredictable benefits coming from such a contact as well.

    I myself have read a little and I've never seen anything to the effect of Alnico's losing strength of any significance within 20 years let along one year - unless subjective to some other freak magnetic field of severe magnitude that won't occur in their normal lifetime - or excessive heat like from grinding. I've never heard the piece regarding Garcia before or the like regarding anyone else. Never looking into it but I've read that magnetizing/remagnetizing is cheap to have done. The appeal for alnico mags in part is based around the desireable affects they do have on tone.
  5. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    Bill Lawrence knows a thing or two about pickups, and he has this to say about magnets:

    "Ceramics vs Alnico
    When I read that ceramic magnets sound harsh and alnico magnets sound sweet, I ask myself, " Who the hell preaches such nonsense?" There are harsh-sounding pickups with alnico magnets and sweet-sounding pickups with ceramic magnets and vice-versa! A magnet by itself has no sound, and as a part of a pickup, the magnet is simply the source to provide the magnetic field for the strings. The important factor is the design of a magnetic circuit which establishes what magnet to use.

    Though ceramic magnets cost less than alnico magnets of equal size, a well-designed magnetic circuit using ceramic magnets costs much more than the six Alnico 5 magnets of a traditional single coil pickup!

    [size=-1]Aging [/size]

    Before the introduction of alnico magnets in 1935, permanent magnets were not quite that permanent. During a certain time, they lost a good amount of magnetism till they finally reached a stable condition. The process to accelerate this decay was called in the industry, "magnetic aging." In modern science, it is called "stabilizing." Since the ‘50's, we use Alnico 5 magnets which lose, under normal conditions, less then half a percent per 100 years.
    How do we achieve normal conditions? [/size]

    Alnico magnets are shipped by the manufacturer in a non-magnetized condition and will not be magnetized until a pickup is completed.

    [size=-1]How to maintain normal conditions?[/size]
    After magnetization, avoid any close contact with other pickups or magnets facing either north to north or south to south with their magnetic poles. Don't ever throw pickups random in a drawer; you may either use a keeper on each side of the magnetic poles or carefully place them with the north facing the south pole of the other magnet. ( For tele players, remember that the iron backplate of a traditional tele pickup functions as a keeper which increases the stability of the magnets.)

    Once pickups are in a guitar, there is very little to worry about. That your pickups lose some of their magnetism when you lean your guitar against an amp is nothing but a fairy tale. Or, that pickups lose some of their magnetism when you drop them on a concrete floor is just another fairy tale -- alnicos and ferrites will break before they have any measurable losses. Magnets are sensitive to heat, but so is your guitar. However, heat can be a severe problem when an Alnico 5 magnet is exposed to temperatures above 1000 F, approaching its Curie temperature of 1634 F. At these temperatures, Alnico 5 undergoes structural changes and cannot be re-magnetized. Why do I mention this? Because it happens quite often, when someone doesn't like the unbalance in output of a pickup with staggered magnets and goes to a bench grinder or a belt sander to grind a magnet down. You take a chance that a magnet gets too hot and becomes damaged."
  6. luknfur


    Jan 14, 2004

    Which brings up another point you will run across: just like conflicts among scholars or physicians, be prepared for actual or apparent conflicts it what they're saying.

    This is a clip from the Kinman tone workshop:

    It is a fact that Ferrite (Ceramic) magnets play absolutely no part in tone shaping of a guitar pickup simply because they are non-conductive, non-metal magnets and do not influence the electrical behaviour of the coil, and exchanging these with Samarium Cobalt magnets has similar sonic results; in other words these magnets are completely toneless / soundless (ie they play no part in tone shaping). On the other hand we have Alnico, the magical magnet. Alnico is unique because it imparts a TONE flavour and certain dersirable performance characteristics into the sound. It does this because it is metallic and conductive and does influence the electrical behaviour of the coil. There are those that will tell you that a clever designer of Samarium Cobalt or Ferrite magnet pickup can somehow, miraculously, compensate for the missing Alnico by clever magnetic circuit design, this is simply not so. Magnetism is just magnetism, but 'coil core' material is a whole different story...

    To me it's a moot point whether the magnet itself "has a tone" or influences other factors in a way that require the presence of a given magnet to get that tone - without it you won't get it.
  7. Audere

    Audere Supporting Member Commercial User

    Apr 7, 2005
    South Beach, OR
    Owner: Audere Audio
    You might want to check out

    Permanent Magnet Materials and their Application
    Peter Campbell, Cambridge University Press
    ISBN 0 521 56688 6

    While not written about pickups it discusses stability of magnets, the magnetizing operation etc., and it is readable for an engineering book.
  8. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    But the "without it you won't get it" idea is precisely the part that's dubious IMO. You're taking that as a given, and I think it remains to be proved.
  9. luknfur


    Jan 14, 2004

    actually I'm not taking it as a given, that's just what that guy was saying and that was my point about conflicting information. Apparently it didn't come across as I'd intended.

    The ear is where it's at. Specs and all the technical jargon (for pups, cabs, whatever) to me can be of some use or may be misleading. The bottom line is if a given bass player can't hear it or it's of no consequence to him for whatever reason regardless, then it doesn't matter to him. If he can hear it and it's of consequence to him for whatever reason than it does matter. Each player draws his own conclusions.

    To me in a given situation a pup either works to my taste or not. I really don't care what it's made of or how it's constructed. Change variables and the pup may not be so appealing, or it may be more appealing. You know when you do it.

    In my experience I have found that MM pups with alnico 5 mags put out a unique tone. The Nord, Ray, and Carvin alnico 5 MM's I have had all sounded close enough to each other where it's was splitting hairs, if I could tell at all. The Sterling it seems was very similar if not the same as well. The Barts, Lane Poors, Bongo, SD ceramic are defintely a different story. Whether it's the mags or other factors in construction I don't know and don't really care but the alnico's sounded basically the same and the others didn't sound like the Alnico.

    In other pups I've never really drawn any conclusion about alnico but a lot of pups I have no idea what mags are in them. The only reason I know about the MM's is becuase I knew what pups had the alnico 5's in them and the tone variation was obvious.

    From a logical standpoint, Alnico is a more expensive material than ceramic and if it made no difference, large numbers of respected manufacturers wouldn't be using more expensive materials to no end.

    Ragardless, the Ear is where it's at and it's for each player to decide for himself. Blondes/Brunettes Fenders/Alembics, to each his own.

    By the way, here's that link and I think the guy had soundclips or something FWIW:
  10. Richard Lindsey

    Richard Lindsey

    Mar 25, 2000
    Metro NYC
    I hear you; I probably misconstrued what you were saying. I agree with you on letting the ear be the judge. I don't care what it's made of if it sounds good, and I can't say that I've notice familial resemblances. From what I can tell, it seems to be about the design of the PU as a whole, not the magnet material.

    Re relative costs, Bill Lawrence had this to say: "Though ceramic magnets cost less than alnico magnets of equal size, a well-designed magnetic circuit using ceramic magnets costs much more than the six Alnico 5 magnets of a traditional single coil pickup!"
  11. luknfur


    Jan 14, 2004

    yeh, no doubt I've read it before unless it's changed recently cause I read through his whole site once. Have had a few of his pups. They've all been a brighter more clear sounding pup so far. More mellow than warm in that aspect. Depends on what you want. The sound is what matters. I've got pups I've paid $3 for I like as well, as pups I've paid a couple hundred for, better even actually for some.

    That alnico mags are more expensive than ceramic has just been a repetitive theme in readings not experience of purchase. There's different mixes of alnico and ceramic and I've read about recent Chinese purchases of alnico mags so I wouldn't be suprised if you could probably get alnico from China cheaper than ceramic in the U.S.

    I've never bought either mag and it's unlikely I ever will.
  12. Thanks for the replies and discussion, there's some good info above. Here are further answers to some of my questions:

    - Is there a limit as to the number of times a cast alnico magnet can be remagnetised?


    - What is the process of remagnetising and calibrating pickups or magnets?

    The magnets are magnetized to the maximum saturation point. Following that, they will self-demagnetise slightly to a stable value of around 95%.

    - What tools, other than a guass meter, are required for remagnetising magnets?

    The magnetic flux of magnets are measured with a fluxmeter.

    Just on the extract provided by Richard from the Bill Lawrence site, alnico magnets are not always shipped in a non-magnetised state. At least one manufacturer gives the option of shipping the magnets in a magnetised and non-magnetised condition. Shipping the magnets in a magetised state requires specialised packing. So, it seems it's better to have them shipped unmagnetised unless the magnetism can be checked on arrival.
  13. Rick Turner

    Rick Turner

    Jul 14, 2004
    Pickup design is an art wrapped in science. The only real way to learn is to read everything you can, and then start winding. There are no specs that really tell you how a pickup "sounds". Yes, you can run frequency response tests on the coils, but that doesn't tell you how the pickup interfaces with a string. To learn that you will just have to start winding. That's how every one of us who knows what they're doing has learned...and we don't all necessarily agree upon everything. For instance, the statement that magnets have no tone is true, but in a magnetic circuit they affect the inductance of the coil which does affect tone. Everything in a pickup affects tone. I even hear the difference between superglue coil potting, shellac potting, and parrafin wax potting as each affects the mechanical resonance of the coil structure. Start winding.

    Is there a constant theme running through my comments? Start winding...learn the science so you can be free to create the art...listen...think about the variables that are hard to define...start winding.
  14. luknfur


    Jan 14, 2004
    There you go. I don't know how often Rick reads this stuff but he doesn't often take the time to comment.
  15. Rick, thanks for your comments. These days, I'm more cautious when selecting projects to complete. Working as a software engineer, I tend to spend time in the requirements and design phases prior to building - job habit. For me that means a lot of research, not only in making a case for building them in the first place but other things ranging from tools to suppliers, planning, cost effectiveness practicality and risk. Anyway, the main questions I had are now answered and I've made an order for most of the parts, so I'm looking forward to getting started.

    luknfur and Richard thanks again for driving the topic.
  16. luknfur,

    You've done some substantial work in testing a whole range of different pickups. Do you have the specs of the Music Man bass pickup, pre Ernie Ball? I get the feeling you're not into the intricate technicalities, just the sound, but this will help a great deal for designing a similar humbucker based on that design. For example:

    - magnet type (alnico 5?)
    - magnet diameter & length (9mm x 19mm?)
    - flatwork thickness, width & length
    - inner height of the bobbin. From inner top to inner bottom of bobbin
    - wire guage (42 awg?)

    anything else I've missed.
  17. luknfur


    Jan 14, 2004

    Haven't a clue. I just drives 'em I dont makes 'em.

    I've got an EB Ray pup and the guy I bought it from knows Rays and he had early Ray pups and said they didn't sound different to him than the EB models. I've never had one so I don't know but this guy I consider a reliable source. That combined with the fact I've never run across a liked designed pup other than the Ray that sound so similar regardless of maker.