Eddy currents - Not Wally or Beaver currents 8-)

[R.G.]

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

[corduroyew]

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 I’ve 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 I’m not sure it’s going to sound the way the alnico buffs want it to sound so to market it you will have to say it’s a paf on crack, but we aren’t just talking regular ol’ crack, ist the super beefed up Charlie sheen crack. Yeah, it’s that good. Then people might take a look.

Sorry… I’m rambling… I’ll stop now

[R.G.]

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.

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.

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.

If you experimented with it, I would love to see your results. Finding the magnets you need is small quantities would be thought but I’ve 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 I’m not sure it’s going to sound the way the alnico buffs want it to sound so to market it you will have to say it’s a paf on crack, but we aren’t just talking regular ol’ crack, ist the super beefed up Charlie sheen crack. Yeah, it’s that good. Then people might take a look.

Sorry… I’m rambling… I’ll 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...

[Joe Gwinn]

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.

[R.G.]

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.

[Joe Gwinn]

(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.

[Joe Gwinn]

Eddy currents and Lenz's Law

http://en.wikipedia.org/wiki/Lenz's_law

[DrStrangelove]

The long skinny on magnets

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

[DoctorX]

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

[David Schwab]

Do metal magnets even suffer from eddy currents? My impression was that it was just non magnetic objects.

[Possum]

:-)

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....

[David Schwab]

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.

[Joe Gwinn]

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.)

[soundmasterg]

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

[David Schwab]

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.