Tweeking the magnets

[wrnchbndr]

I've just finished a prototype electric mandolin using a P90 style pickup of my own construction. One of the problems with the prototype is a weak response of the E-string pair. This pair of strings in an octave above the pitch of a guitar. The difference in string response is subtle unless you're looking for it and then its obvious. I like a P90 coil/magnet configuration and find it the easiest to build from scratch making my own bobbins and only needing to buy wire and bar magnets but I'm thinking that to address the weak E-strings (which apparently a common thing with magnetic mandolin pickups), I'm going to try a Fender style pickup with magnetic slugs and use a stronger magnet type for the E-string(s) slug. With the choice of Alnico 2,3, 5, and 8, what would you folks consider to be a good combination? Is Alnico5 so much stronger that it would be too much of a difference? I have no idea of the impact to signal level from an increase in magnetism.

Another question, Does the potential strength of the magnet increase with the length of the slug? Does it increase with the diameter of the slug?

 

[DavidRavenMoon]

Re: Tweeking the magnets

Stronger magnets will give a louder and brighter tone. The extra brightness alone can help you hear those strings.

Yes, longer rod magnets can be stringer. Same with thicker bar magnets. A larger diameter rod magnet will be stronger still, because the pole has a greater surface area.

With P-90 style pickups the steel poles and keeper increase the inductance. That increases the output and warms up the tone.

On the old DeArmond “monkey on a stick” archtop pickup, they used different diameter magnets, having larger ones under the weaker treble strings. They also wound the coil in two parts so those strings could have more output. So a split pickup could be a good idea, and you can make it hum canceling that way too.


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[wrnchbndr]

Re: Tweeking the magnets

Well I've ordered alnico 2 and alnico 5 slugs. The Al5 slugs are for the E strings.