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Thread: Eddy currents - Not Wally or Beaver currents 8-)

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    Eddy currents - Not Wally or Beaver currents 8-)

    Is alnico made in rods which are perhaps 25mm long and 0.02" diameter or square? If Alnico eddies, can we make laminated alnico?

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    Don't we like the eddy currents we get from alnico? I thought that the increased inductance was what gave us that classic "alnico sound". Take away the reason for using it and we might as well stat using ceramic. I dunnow. I've had a half bottle of Morgan and it's way past my bedtime I might not be thinking straight on this one..

    If you experimented with it, I would love to see your results. Finding the magnets you need is small quantities would be thought but Iíve found that when I making a product I never order enough of something so now I buy everything in bulk which makes getting parts easier. Anyway back to the point, I think you could do what you are trying to do bt Iím not sure itís going to sound the way the alnico buffs want it to sound so to market it you will have to say itís a paf on crack, but we arenít just talking regular olí crack, ist the super beefed up Charlie sheen crack. Yeah, itís that good. Then people might take a look.

    SorryÖ Iím ramblingÖ Iíll stop now

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    Quote Originally Posted by corduroyew View Post
    Don't we like the eddy currents we get from alnico?
    Maybe. I don't know that anyone's ever looked. There is speculation that alnico has eddy current losses and that we like them. There's also speculation that we like the compressed sound of alnico being overdriven by a string being plucked - which may happen, but I can't see how it could.

    When I can't understand something that I want to understand, my approach is to think of a way to eliminate it and see if I miss it. That way I'll know. Hence the test for eddy current in Alnico.
    Quote Originally Posted by corduroyew View Post
    I thought that the increased inductance was what gave us that classic "alnico sound".
    Eddy currents is not equal to increased inductance. Greater permeability is how you get increased inductance. Eddy currents come with greater conductivity.
    Quote Originally Posted by corduroyew View Post
    Take away the reason for using it and we might as well stat using ceramic.
    I'm with you on that. I'm trying to lay out how to test for what the reason for using it really is in ways we can measure.
    Quote Originally Posted by corduroyew View Post
    If you experimented with it, I would love to see your results. Finding the magnets you need is small quantities would be thought but Iíve found that when I making a product I never order enough of something so now I buy everything in bulk which makes getting parts easier. Anyway back to the point, I think you could do what you are trying to do bt Iím not sure itís going to sound the way the alnico buffs want it to sound so to market it you will have to say itís a paf on crack, but we arenít just talking regular olí crack, ist the super beefed up Charlie sheen crack. Yeah, itís that good. Then people might take a look.

    SorryÖ Iím ramblingÖ Iíll stop now
    That's OK, you have a very valid point. Take away what makes alnico good, and you have made a less desirable pickup. I'll probably never sell a single pickup - no desire to, plus I've been a shop keeper and didn't like it. But maybe I can find out what does make alnico good and then we can make up some way to concentrate the goodie somehow.

    Now all I gotta do is find alnico magnet ... wires...

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    Quote Originally Posted by R.G. View Post
    Eddy currents is not equal to increased inductance. Greater permeability is how you get increased inductance. Eddy currents come with greater conductivity.
    Greater permeability does increase eddy currents, by increasing the magnetic field strength. A good way to approach this is to look at the equations for skin depth, which depend on both permeability and conductivity.

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    Quote Originally Posted by Joe Gwinn View Post
    Greater permeability does increase eddy currents, by increasing the magnetic field strength. A good way to approach this is to look at the equations for skin depth, which depend on both permeability and conductivity.
    Coool. Help me understand this.

    (1) I had this idea that I could minimize eddy currents in alnico magnets the same way we minimize them in transformer iron, and the same way we reduce skin effect in wires at high frequency, by making one dimension smaller. Literally, using a bundle of alnico sticks instead of a solid alnico pole. At least, that would provide a test for whether eddy current losses in the magnets was a factor in pickup design.
    (2) corduroyew said "Don't we like the eddy currents we get from alnico? I thought that the increased inductance was what gave us that classic "alnico sound".", which I interpreted that he may have mixed up eddy currents and inductance. Near as I can tell from the equations, inductance doesn't depend on the eddy current suseptibility or the actual currents in coil cores. Eddy currents are losses, inductance is storage.
    (3) holding that perhaps incorrect idea, I said "Greater permeability is how you get increased inductance." indicating my belief that eddy currents don't increase inductance, but permeability does; I did this thinking that corduroyew had mixed up a term or two.
    (4) I did not say that permeability does or does not increase eddy currents. Only that eddy currents don't change inductance. Which I think is true.

    So if you can help me here I'd appreciate it - which part of this did I get backwards?

    I'm with you that increased permeability can increase eddy current losses in a particular pole piece; that's not in question. But since my question was about the same material, alnico of one grade or another, divided up into fine pieces to prevent eddy current losses in the magnets and since the magnets provide the only (and fixed) source of magnetic field, I'm confused about what you think is changing permeabilty. It's the same magnet material, same pole piece material, same strings, same air.

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    Quote Originally Posted by R.G. View Post
    (1) I had this idea that I could minimize eddy currents in alnico magnets the same way we minimize them in transformer iron, and the same way we reduce skin effect in wires at high frequency, by making one dimension smaller. Literally, using a bundle of alnico sticks instead of a solid alnico pole. At least, that would provide a test for whether eddy current losses in the magnets was a factor in pickup design.
    In theory, laminating the magnet would work, However, all permanent magnet materials are too hard and brittle for this to be practical.

    (2) corduroyew said "Don't we like the eddy currents we get from alnico? I thought that the increased inductance was what gave us that classic "alnico sound".", which I interpreted that he may have mixed up eddy currents and inductance. Near as I can tell from the equations, inductance doesn't depend on the eddy current suseptibility or the actual currents in coil cores. Eddy currents are losses, inductance is storage.

    (3) holding that perhaps incorrect idea, I said "Greater permeability is how you get increased inductance." indicating my belief that eddy currents don't increase inductance, but permeability does; I did this thinking that corduroyew had mixed up a term or two.

    (4) I did not say that permeability does or does not increase eddy currents. Only that eddy currents don't change inductance. Which I think is true.[

    So if you can help me here I'd appreciate it - which part of this did I get backwards?
    But eddy currents do reduce inductance, by opposing the flux that created them, according to Lenz's Law. This is better described in physics textbooks than EE textbooks. There is a long thread on eddy currents and skin depth in the archives, with links to physics lectures. Search for Lenz's Law

    I'm with you that increased permeability can increase eddy current losses in a particular pole piece; that's not in question. But since my question was about the same material, alnico of one grade or another, divided up into fine pieces to prevent eddy current losses in the magnets and since the magnets provide the only (and fixed) source of magnetic field, I'm confused about what you think is changing permeabilty. It's the same magnet material, same pole piece material, same strings, same air.
    Well, finely divided alnico is magnetically unstable, and will self-demagnetize. Use of high-resistivity material is more practical.

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    Eddy currents and Lenz's Law


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    The long skinny on magnets

    Quote Originally Posted by R.G. View Post
    Is alnico made in rods which are perhaps 25mm long and 0.02" diameter or square? If Alnico eddies, can we make laminated alnico?
    The smallest dimension I see in standard stock sizes is .062" (1/16").
    Maybe five or six dozen of these would be small enough to test the hypothesis
    using a bar-shaped assembly.

    The rule of thumb is that, to inhibit alnico's tendency to self-demagnetize, the
    magnetized dimension should be 4-5 times the size of the shortest dimension.
    It's why we see 3/4" long 3/16" diameter rods so often in pickups.

    An incomplete list of magnet vendors is at:
    http://www.salvarsan.org/magnetics/index.html

    -drh

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    there's more on that same website.....

    Thanks for the link Dr. Strangelove.....

    If you go back a step or two on that same web site, you find these:

    http://www.salvarsan.org/content/alnico.html

    and

    http://www.salvarsan.org/magwire/index.html

    and

    http://www.salvarsan.org/content/fillfactor.html


    DoctorX

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    Pickup Maker David Schwab's Avatar
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    Do metal magnets even suffer from eddy currents? My impression was that it was just non magnetic objects.
    It would be possible to describe everything scientifically, but it would make no sense; it would be without meaning, as if you described a Beethoven symphony as a variation of wave pressure. ó Albert Einstein

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    :-)

    This is interesting but kind of aimed at making pickups that don't sound very good, hi fi. If you want to get rid of eddy currents just use ceramic magnets. Thing is pickups that do use ceramic magnets always have enough metal in them to load the circuit down so you don't get squeaky clean tones....
    http://www.SDpickups.com
    Stephens Design Pickups

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    Pickup Maker David Schwab's Avatar
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    Hi-fi is good for modern bass tones though. Guitar players never seem to like hi-fi pickups, except jazzers like Tuck Andress.

    Ceramic pickups with no metal in them don't have as much output either. The more metal the less windings you need. I have a boatload of steel in my pickups, but not that much wire. They are very clean and bright.

    Those Basslines ceramic Music Man pickups being discussed elsewhere here have big steel poles, and not all that much wire on them. They are only about 2.6K each coil.

    I was real surprised when I was researching Burns Tri-Sonic pickups.... they use a ceramic bar magnet, and a steel base plate! At first I thought that was crazy, but it makes sense. It raises the inductance.
    It would be possible to describe everything scientifically, but it would make no sense; it would be without meaning, as if you described a Beethoven symphony as a variation of wave pressure. ó Albert Einstein

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    Quote Originally Posted by David Schwab View Post
    Do metal magnets even suffer from eddy currents? My impression was that it was just non magnetic objects.
    Any material that is electrically conductive can have eddy currents. The material may in addition be magnetically permeable, so all four combinations are possible, and are seen in practice.


    1. Conductive and permeable: anything made of iron or non-stainless steel. This includes alnico, cunife, and the like.

    2. Conductive and non-permeable: All metals except iron and non-stainless steel.

    3. Non-conductive and permeable: Ferrites.

    4. Non-conductive and non-permeable: Everything else.


    The first two combinations support eddy currents, the second two do not.

    The first and third combinations can generate or enhance/focus magnetic fields. (Assuming no electromagnets are in the picture.)

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    When you researched the Burns Tri-Sonics, did you take a look at the Adesons? The new Burns Tri-Sonics aren't like the old 60's ones from what I've been able to discover, and Adesons are made the same way as the old ones, using the same materials, same winding setup, etc. I picked up some of these Adesons but haven't put them in a guitar yet. They're VERY thin top to bottom, and Ade sent me an email about them that I've posted here in the past. Should be interesting to hear a true air coil when I get around to trying them out in something....

    http://www.adeson.co.uk/

    greg

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    Quote Originally Posted by soundmasterg View Post
    When you researched the Burns Tri-Sonics, did you take a look at the Adesons? The new Burns Tri-Sonics aren't like the old 60's ones from what I've been able to discover, and Adesons are made the same way as the old ones, using the same materials, same winding setup, etc.
    Yes, the new ones aren't the same at all. From what I've read the originals use a bobbinless coil around a ceramic magnet on a steel baseplate. The 6 holes in the cover aren't really for poles, since they're aren't any.

    My buddy has a set of the Duncans that were used in the Guild May guitars, but we haven't opened them up yet. He paid a lot of money for them so he's nervous about having me open them. They are supposed to be made the same way, but I doubt they are as authentic as the Adesons.

    My reason for reading up on them is I plan to building a Red Special and figured I might as well make the pickups myself. Otherwise the Adesons look great.
    It would be possible to describe everything scientifically, but it would make no sense; it would be without meaning, as if you described a Beethoven symphony as a variation of wave pressure. ó Albert Einstein

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    Yeah, I didn't think the new ones were the same so thanks for confirming it. I plan to get one of the new Brian May made Red Specials soon and I'll stick my Adesons in it. You're making your own Red Special? Should be interesting! I'd thought about doing that in the past for myself but I'm more into building amps lately so I decided not to.

    Here's is something that Ade Turner emailed to me after I got my pickups and asked about them. I thought you might find it interesting and helpful.

    Greg

    Regarding the coils - all early European pickups (Hofner / Framus / Hoyer etc..) were built this way. The coil is wound on a removeable chassis - and then completely wrapped in a special armature winding tape (takes ages to learn this - they are ridiculously delicate!). The whole thing is pulled tight - just like lacing up your boots. The magnets are vintage ceramic (similar to Alnico 2). They have been out of production since the early seventies - I have to have them custom made - and they cost a fortune!!! The coils are then placed arround the bar magnets (the holes in the chrome top covers are purely aesthetic). The whole thing is then glued solid to prevent the brass top covers from causing howling. This is exactly how they were made 40 years ago - and they sound great!!!

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    Pickup Maker David Schwab's Avatar
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    Yeah, I'm going to try and make a pretty authentic red special... right down to the neck extending all the way to the bridge. I will likely use a different bridge though, but I'm going to make the May tremolo system. I hate they way they look with a strat bridge!

    I'm also not making it 24 inches. I'll stick with the Gibson scale.
    It would be possible to describe everything scientifically, but it would make no sense; it would be without meaning, as if you described a Beethoven symphony as a variation of wave pressure. ó Albert Einstein

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