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I'm working on it... 8-)

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9/12/2002 6:56 PM
R.G.	I'm working on it... 8-) There's a lot to cover there. I'm putting together some rational info on your questions, which were very apt. R.G.

9/12/2002 7:40 PM

Dr. Strangelove

quote:
"There's a lot to cover there. I'm putting together some rational info on your questions, which were very apt."

At least one of them _wasn't_ apt, viz., "fringing" so please don't worry about it.

Thanks in advance for poking me in a useful direction.

I looked, found that: Since a magnetic flux follows a curved path as often as a straight one, it will bow out of an air gap in a "C"-shaped magnet. This is considered "leakage flux" that is unavailable for work.

In a rod, bar, or U shaped magnet, nearly all flux can be considered fringing flux, but the pickup coils are directly in its path. That flux is doing work and can hardly be called leakage.

As Tony of MasterTone mentioned, a pickup sounds distinctly different when you put windings on bare Alnico than when you have .025" of plastic bobbin separating them.

2D magnetic models under FEMM show that the Alnico rods in pickups have a higher flux density close to rod circumference. This hi-dens fringe has the greatest sensitivity to changes in the circuit reluctance caused by the vibrating guitar string.

If the models aren't too ideal, a .046" E guitar string over an Alnico V humbucker can have a 50-100 Gauss dipole, more than enough to perturb the magnetic circuit in the pickup.

Corrections and clarifications are very welcome.

I'm extremely curious about that orthocyclic winding pattern, though. Got some dirty pictures? ;-)

;-)

9/12/2002 7:33 PM
R.G.	It looks like air cored... ... if you can believe this : http://www.magnetweb.com/Sect1C.htm Surprised me. Good stuff in that set of info. They get into discussing the inductance of a solenoid coil with an permanent magnet inside, which is pretty close to the info we're looking at. R.G.

9/12/2002 8:15 PM

Dr. Strangelove

Sometimes very close. Yea, yer rite. I was confused.

I dug up a a list of relative permeabilities so as to as to forestall any handwaving arguments I might initiate:

1.000 - AIR
1.034 - SmCo 20 MGOe
1.048 - NdFeB 37 MGOe
1.051 - Ceramic Ferrite 7
1.103 - SmCo 27 MGOe
1.110 - SmCo 24 MGOe
1.178 - Ceramic Ferrite 6E
1.223 - NdFeB 10 MGOe (Bonded)
1.252 - Ceramic Ferrite 1
1.269 - Ceramic Ferrite 8
1.500 - Alnico 2
1.500 - Alnico 5
1.976 - Ceramic Ferrite 5
3.300 - Alnico 6
6.678 - Alnico 8

SmCo = Samarium Cobalt
NdFeB = Neodymium Iron Boron

This suggests that A8 makes for a high inductance pickup, but you might not want to listen to it because the high coercivity would make it sound quite harsh.

There are a lot of variations within Alnico 2's and 5's and you can never quite tell which unless you buttonhole the vendor's engineer. Even then, they won't guarantee B, Hc, and BHmax closer than 20%.

Group Arnold has a good body of technical magnet info:

<http://www.grouparnold.com/mtc/index.htm>

-drh
--

9/12/2002 8:22 PM

Re:Alnico 8--Quite the opposite!

Actually, on the Alnico 8's, it quite the opposite. I learned about Alnico 8 from Lynn Collins several years ago.
They're an extremely sweet sounding magnet. Very sensitive, so they sustain for a very long time. You've got to lower them a bit further than Alnico 5, but once you find "the spot" there's nothing like 'em.
They're pretty expensive though, that's why I dropped them from my line of pickups.

Wolfe

9/12/2002 8:51 PM
Dr. Strangelove	Thanks, good to know. What type of coil was it and _roughly_ how much wire did you need to put around it? A saleman said A8 was so hard and brittle that they didn't like working with it. On a 50 piece order, it got down to $8 ea. on humbucker-sized bars. Ouch and no thanks. -drh --

9/12/2002 9:21 PM

These were strat coils mainly. They had the most beautiful sound.
I managed to find Alnico 8 'bucker bars for a great price. Heress the quote:
Alnico 8 .130 +/-.002 x 2.500 +/-.010 x .500 +/-.002 -m-; magnetized
100 pcs - $2.24 each 250 pcs - $1.68 each 500 pcs - $1.12 each
lead time approximately 4 to 6 weeks aro to ship

That's pretty damn good, considering I was paying about $6 each for strat/tele rods from the old source.

Wolfe

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