harp pickup

Classic Spartan sewing machine from 1959, gets second job as a pickup winder.  Purrs along just like a Merlin V-12 (which they always say, runs like a sewing machine). Here's the "cruise control". So at slightly over 2 RPM, 2000 windings would take almost 17 hours.  Except that I dare not leave it running non-stop, as the control pedal gets way too hot and makes scary smells.  So I'm running it at about a 50% duty-cycle, 15 minutes on, 15 minutes off.  So, this could take several days.  Or, maybe my speed control that I ordered will arrive before this is done...

Well, same experience as when I wound a replacement pickup for my Vox Spitfire: many failed attempts to get one success.  I set up my sewing-machine pickup winder, with customized mounting and wire-guides for the big harp pickup.  I found that I had to go agonizingly slowly, to avoid breaking the wire (chalk up several attempts of 50-100 turns each).  Removing failed windings in order to start over got to be a regular chore, so I put a special notch in the side of the bobbin so that I can easily cut away the old windings with a hobby knife.  Good thing I have an ample supply of #42 wire, the waste is non-trivial. I found that I did not need to hand-feed the wire to spread it over the bobbin.  The bobbin is narrow enough that with just feeding from the centerline, the wire spreads nicely by itself.  Therefore, I was able to set up the machine to run unattended, using a carpentry clamp to set the position of the "accelerator pedal" on the sewing machine....

Here are photos of the beginning of fabrication of the acrylic bobbin inner core, and the steel backing plate. The bobbin is formed from two strips of clear acrylic (0.08" thick each), epoxied together, with a paper strip sandwiched in the middle. The backing plate I cut from the steel enclosure of a broken VHS player. I used the same screws which will ultimately be the polepieces, to clamp the acrylic strips together during the epoxy process.  However, the screws here are going from the top; in the final arrangement, the screws will come up from the bottom (through the metal backing plate), and only the threaded ends will protrude slightly above the top surface of the bobbin.   The main trick with the epoxy, is getting the paper to stay centered as the pieces are clamped.  This clamping, intentionally, causes much squeeze-out of the epoxy, leaving only a nice, thin, uniform layer, free of air bubbles; however, the flow pattern tends to drag the paper sideways.  I fo...

 Sat 24 Aug 2024 08:03:14 PM PDT A single-coil pickup for my "Little Harp" (actually, a 15-string diatonic zither).  Maureen and I want to use this instrument for accompaniment in performing some Sufi love songs.  Rather than trying to mic-up the harp, I want to see how it sounds with a pickup. A secondary motivation for building this pickup is to experiment with and develop techniques for making pickups for my Pandalon and other harpsichords which I plan to build.  The size and shape of this pickup is roughly the same as what I'll be using on those keyboard instruments (one pickup per octave, I hope). I already have the fixtures built, which attach to a sewing machine to turn it into a pickup winder, so I'll see if I can make that work here. I'm first going to try one long bobbin (7+3/4").  If that doesn't work (i.e., if the tension variations are too extreme and the wire can't be prevented from snapping), I will try a series of shorter bobbins, such...