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baseplate differences


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11/6/2004 8:11 AM
anonymous baseplate differences
Can someone tell me why some p/u makers use brass for the baseplate material in humbuckers, and some use steel or nickel silver?  
 
Thanks
 
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11/6/2004 6:54 PM
anonymous
Some pickup companies use brass because it's much cheaper than nickel silver.  
Think Dimarzio.  
Brass is also a tone-killer when it comes to base plates.
 
11/7/2004 6:12 PM
Dave Stephens
Oh My God!!!! There are TWO anonymouses here! OK, this opens up another subject, WHY is brass a tone killer versus stainless or nickle silver, and what effect does this have in pickup covers? Davanymous
 
11/8/2004 2:04 AM
anonymous
The effect on brass in pickup covers is extremely noticable.  
As a test, buy a brass humbucker cover from Stew-Mac, and a nickel silver cover from Allparts. Test them both. The brass cover will be much darker and muddier.  
 
As a second test, wind a P-90. Make a brass base-plate, and then a nickel silver plate. You could scrounge one from a Duncan or Gibson, I'm sure.  
Test them both. The brass plate will be darker and muddier, but not quite as much as the covers test.  
 
Do the same for Telecaster neck, with the cover. A Stew-Mac brass cover, and a nickel silver cover from Jason.  
 
What puzzles me is that nickel silver is mostly brass anyways, with just enough nickel in it to make it look like silver.  
 
As to WHY brass is a tone killer? I don't know. Bill Lawrence would probably chalk it up to eddy currents!
 
11/8/2004 4:12 AM
Anonymously Anonymous
Its even worse Dave!  
 
Greg
 
11/8/2004 5:35 AM
RobB
Interesting point about the eddy currents. I suppose the electrical conductivity of the alloy used to make the base plate/pup cover will influence how easily eddy currents can develop.  
The tabulated information at this site says nickel silver is less conductive than brass.  
http://www.eddy-current.com/condmat.htm  
I'm guessing a stainless base plate should produce a fairly bright sounding pickup, all things being equal with the coil and magnet/s.
 
11/8/2004 7:50 AM
Joe Gwinn

On 11/8/2004 12:35 PM, RobB said:  
quote:
"Interesting point about the eddy currents. I suppose the electrical conductivity of the alloy used to make the base plate/pup cover will influence how easily eddy currents can develop."
 
 
That's exactly correct. (The magnetic permeability also matters, but these alloys all have the same incremental permeability as air.)  
 
[QUOTE]The tabulated information at this site says nickel silver is less conductive than brass.  
http://www.eddy-current.com/condmat.htm  
I'm guessing a stainless base plate should produce a fairly bright sounding pickup, all things being equal with the coil and magnet/s.[/QUOTE]  
 
 
To put some numbers on it:  
 
Silver (pure): 1.62 microhm-centimeter  
 
Copper (pure): 1.72 microhm-centimeter  
 
Brass, yellow (alloy 260): 6.16 microhm-centimeter  
 
Alnico 5 (Cast): 50 microhm-centimeter  
 
Stainless Steel (300-series alloys): 72.0 microhm-centimeter  
 
Nickel Silver (alloy C757): 130 microhm-centimeter  
 
The larger the microhm-centimeter value, the smaller the eddy currents, in inverse proportion to the value.  
 
 
The thickness of the metal sheet also matters, thicker sheets yielding larger eddy currents, in direct proportion to the thickness (for thin sheets at audio frequencies). Baseplates seem to be made of 0.032" sheet, while covers are 0.022" or 0.025", at least for the ones I have looked at.  
 
Baseplates intercept less of the changing magnetic field than do covers, so the cover will have the greater effect on sound, as observed.  
 
Stainless steel is stiffer and stronger than nickel silver, so a stainless steel sheet can be thinner and yet achieve the same mechanical stiffness (which varies as the cube of thickness).  
 
Nickel Silver is prettier, though. A classic solution seems to be a stainless steel baseplate and a nickel silver cover.
 

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