Making of the dual single coil pickup for my MSA Universal 12 string
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Original MSA pickup replaced by home made switchable single coil-humbucking pickup

My MSA "The Universal" 12-string is a great sounding instrument, but after I started playing the instrument after I  picked it up at MSA at the end of my holiday trip in the US in 1981, I found that the thinner plain strings,  but especially the 3rd string had a fraction less volume than the rest.
I got used to it and solved it by plucking the string a little harder.

As a luthier with experience in electronics and knowledge of how pickups work, I initially suspected that the magnet might  have lost some of its field strength. But that turned out not to be the case.
Because the 4th and 1st strings also had slightly less volume, albeit to a much lesser extent than the 3rd string, the cause  is to be found more in the filtering effect of the coil. Given the length of the coil of a 12-string pickup, the capacity is  significantly more than that of a single coil pickup of an electric guitar.

From my experience making my own pickups for the bass guitars I build, I know that if a pickup for a 6-string bass has to sound  like the one for a 4-string, then the number of windings has to be reduced slightly.
So when I decided to also make a new pickup for my MSA, it had to have multiple options with a well-balanced frequency response.  It had to be a humbucker with the possibility to also use it as a single coil pickup where the difference in volume between single  coil and humbucker should not be too large

For making the bobbins I use printed circuit board for the flatworks, glued onto a plastic core with CNC pre-cut holes.  Thus the Alnico V pole pieces can be mounted later and will be adjustable in heigth if needed. The copper outside will act as shielding.  The coils are wound with 3 taps for different output and waxed.  After assembly and connecting the top and bottom with copper foil for a full shielding, the pickup is moulded with resin into the rosewood cover

The pickup can be used as a standard humbucker with both coils in series or in parallel mode.  In single coil mode you can choose between the rear or front coil with the option between normal or hot output.  All selectable with a 6 position rotary switch resulting in different frequency characteristics within a not too large difference in volume.