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Insulating baseplate from Alnico magnet


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12/1/2004 8:05 AM
Alan Sato
Insulating baseplate from Alnico magnet
Does anyone know what would happen to the sound if I put tape on the baseplate to electrically insulate the alnico bar magnet and pole pieces from the baseplate? Is it worth the trouble? I figure it will eliminate electrical eddy currents. Will I end up picking up rf noise because the magnet and poles aren't grounded? I am in search for the most detailed and clean sound I can possibly obtain.
 
12/1/2004 12:16 PM
Dr. Strangelove

Alan Sato wrote:
quote:
"Does anyone know what would happen to the sound if I put tape on the baseplate to electrically insulate the alnico bar magnet and pole pieces from the baseplate?"
Yes.  
 
It would soften the pickup's high frequency response and , if you sold pickups on the basis of that feature, it would put you in violation of a DiMarzio patent for that technique.  
 
-drh  
--
 
12/1/2004 1:11 PM
jason lollar

"if you sold pickups on the basis of that feature, it would put you in violation of a DiMarzio patent for that technique"  
 
yor joking right? All old fender tele pickups have tape over the magnets on the bottom.
 
12/1/2004 2:33 PM
Dr. Strangelove

Jason Lollar wrote:[QUOTE]yor joking right? All old fender tele pickups have tape over the magnets on the bottom.  
[/QUOTE]No joke. Dimarzio probably hasn't asserted patent rights... not yet. I'll try to look these up.  
 
-drh  
--
 
12/1/2004 10:44 PM
Dr. Strangelove
Dimarzio patent 5,399,802
Issued March 21, 1995  
 
quote from patent abstract:  
"The strength of the magnetic field is reduced a desired amount to achieve pleasing tonal quality, by providing a gap in the magnetic circuit between the magnet and the pole pieces."  
 
quote from summary of the invention:  
" In the embodiments described, the spacing is provided by a non-magnetic element, which may be made of any non-magnetizable material such as aluminum, brass, plastic, etc., inserted between the poles of the magnet and their respective pole pieces, or by an air gap, the reduction in intensity of the magnetic field being dependent upon the magnitude of the spacing."  
 
If this is a patent of prior art, a case could be made for its challenge to Pubpat.org.  
 
-drh  
--
 
12/1/2004 4:15 PM
SK Re: Insulating baseplate from Alnico magnet
I'm don't think this is right. The load placed on the magnet doesn't change significantly, but by placing the magnet in direct contact with ground (no tape) the upper high edge gets bled off very quickly. I have tested this in my dualtone HB design which uses a nickle frame and alnico poles for the "strat side".
 
12/1/2004 7:08 PM
Joe Gwinn

On 12/1/2004 3:05 PM, Alan Sato said:  
quote:
"Does anyone know what would happen to the sound if I put tape on the baseplate to electrically insulate the alnico bar magnet and pole pieces from the baseplate? Is it worth the trouble? I figure it will eliminate electrical eddy currents."
It will have little or no effect. The eddy currents are already parallel to this tape layer, and so will not be blocked. To the first order, the eddy currents are parallel to the turns of wire in the coil.  
 
 
quote:
"Will I end up picking up rf noise because the magnet and poles aren't grounded?"
RF, probably not. AC hum and buzz, very possible; that's why people ground everything. If you really want to stop eddy currents any yet still eliminate the buzz pickup, ground the magnet and poles through a 0.25-watt ten or hundred ohm carbon resistor. Eddy currents are very low voltage, and even such a small resistance will effectively block them, while electrostatic hum and buzz pickup is very high impedance.  
 
 
quote:
"I am in search for the most detailed and clean sound I can possibly obtain."
Laminate the poles and use a stainless steel baseplate with ferrite magnets. (No resistor needed.) This will pretty much kill all eddy currents.  
 
It may be a bit bright sounding, I would guess. A brass cover could tame it. Experiments required.
 

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