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previous: R.G. There's a lot to cover there. I'm p... -- 9/12/2002 6:56 PM View Thread

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

9/12/2002 7:40 PM
Dr. Strangelove
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Re: I'm working on it... 8-)
RG wrote:
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? ;-)  
 
-drh  
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