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coupling magnet to adjustable polepieces

5/6/2004 6:39 AM
coupling magnet to adjustable polepieces
in the typical p90 construction, the two wafer alnico magnets are coupled to the adjustable screws via an intermediary steel piece through which the six screws penetrate. this intermediary piece is precision machined and serves mainly to enhance transmission of the magnet flux into the screws.  
my question is if this intermediary steel piece were not present, would the performance result be indistinguishable?  
i ask this because i have another p90 whose wafer magnets directly contact the six screw polepieces. of course the magnets contact the screws merely at a tangent (in comparison to 360 degrees if using the intermediary steel piece).  
does anyone have suggestions which way is better, if any?
5/6/2004 1:34 PM
Sheldon Dingwall

I can't comment on this directly, but I questioned the relationship between the amount of surface contact and how much force gets transfered. Rudimentary tests couldn't detect a difference between pin-point and larger surface area contact between the magnet and pole.
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5/6/2004 2:08 PM
Andy C

Not sure what you mean in the last part of your post about "meeting at a tangent" and "360" degrees.  
The pole screws are vertical through the coil, and the magnets are flat under the coil. I reckon this should be a 90' angle.  
Do you mean what it the difference with or without the metal spacer between the magnets??  
Why not just take it off and listen??
5/6/2004 3:32 PM
Fred Hammon

We have discussed using steel extra steel in pickups before. It started out as a discussion around the steel plates in tele pickups I think. The steel should indeed make the pickup sound different if there is enough of it. My guess would be "brighter". The pickup I'm making has eight steel, insulated laminations in it... like in an electric motor, between the magnets and pole pieces.  
There is a lot of physics happening there and I wish I understood it better.
5/6/2004 5:01 PM
Fred Hammon

Here is a cad drawing I did of my pickup. One of the magnets was removed to show the steel lamination stack (light blue color)
5/7/2004 12:47 AM

meeting the tangent means both alnico wafers edging contacts the polepiece screws at a point tangent on their shafting threading.  
360 drgrees means the intermediary steel piece surrounds the polepiece screw threading 360 degrees.  
yes, i mean what is the difference with or without the intermediary steel piece being installed.  
two different pickups are involved, one with, the other without. i can't make out any audible difference. the scope definitely does show a difference though.
5/7/2004 1:23 AM
Dr. Strangelove
hewo wrote:
"yes, i mean what is the difference with or without the intermediary steel piece being installed."
With the steel, there is more output and a more dynamic sound that can become harsh if you aren't careful.  
The steel piece is a better magnetic conductor than an air gap so you deliver more magnetic energy to the guitar strings at the expense of a slightly higher "work load" on the magnets.  
Dimarzio actually patented the use of a controlled gap between magnets and screw poles although I think it was for PAF style humbuckers. Apparently, the air gap doesn't need to be large, only .003" to .005", about the thickness of a dollar bill or sheet of 20 weight paper.  
It's all there at the US Patent & Trademark Office site if you have the time/patience/desire to dig through it.  
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