harp pickup

Here's the new hum-bucker coil, with plexiglass brackets to mount it above the signal coil on the little harp. In the initial test, I was pleased to find that this coil works very effectively, to cancel out a large part of the hum -- I won't say 100%, but pretty good.  I attached it above the "live" coil with blue tape, and temporarily tacked the wires into parallel with the live coil.  I found that in one polarity, the hum was substantially cancelled.  In the other polarity, or when not connected at all, the hum was just about the same: i.e., really bad.  So, this is a success, and I now have the epoxy drying on the "permanent" mounting, with the wires soldered in the experimentally-verified correct polarity. In the future, for harpsichords and such, I'll try to come up with a two-layer bobbin design that lets me do this with a single unit, like the so-called "stacked single coil" pickups for guitars.  The issue is where and how to place the m...

So I've realized, I'll never be able to live with the amount of hum I'm getting from the single-coil pickup on the little harp.  Certainly, not in live settings, which is the main place I need the pickup for.  In recording, it'll generally be an overdubbing situation since I usually work alone, and so I can just mic the thing up any way I want, and probably sound better anyway. So.  I've created a second plexiglass bobbin, similar to the first (now I start to really benefit from having made a PostScript diagram of the bobbin outlines and pole positions), and I've wound it with 2000 turns of #42 magnet wire.  No magnets or polepieces, though.  According to Mr Internet, this coil should work to cancel the hum, when it is mounted in the same axis but with wiring reversed (no need to wind in the opposite direction, that is spurious thinking AFAIK, though I see lots of people doing it, online).  So now I'm fitting together the brackets to mount this coil, direct...

Some pics of the finished pickup, installed on the "little harp".  My final winding job was 2000 turns, measuring 5.04 kOhms.  The volume control is a 500k linear pot, mainly because that's what I had on-hand.  It'll probably be mostly used either at full-blast, or turned down to zero to mute the instrument. Such a large single-coil pickup naturally has tons of hum susceptibility.  Inconveniently, it seems that the best position to cancel the hum is with the harp held in a vertical position.  To really use this in a live setting, it'll probably be necessary to fashion an adjustable bracket for it, that can attach to a mic stand or similar -- or, maybe a music stand would work.  Either way, there's only one position where the hum is acceptably nulled out; in all other positions it's unbearable.  So this is instructive, vis a vis using pickups like this on a harpsichord.  I think I'll probably have to develop some form of humbucker design.  May...

Here's my new pickup winder, Tortuga, in action on the first (new) attempt to wind this harp pickup.  It's running at about 14 RPM, which is much faster than I was able to get the Spartan to run (it had to either go much slower than this, or else it would freak and jump up to 100 RPM or something, and break the wire).  At this rate, I should have the desired number of turns within a couple of hours.  Pretty fast, for a tortuga! I have a video of this machine in operation:  https://youtu.be/u1EQmWWhWVs Here's the completed coil: 2000 turns.

Slow and steady wins this race.  Even with a solid-state motor speed controller, I was unable to get the Spartan sewing machine to run slowly enough, in a reliable manner, and it kept breaking wires.  Not enough torque to overcome its own inconsistent friction, at such low power settings. So, I built this stepper motor based winder.  555 oscillator drives A4988 stepper driver, running in 1/16 microstepping mode (i.e., the slowest, smoothest mode).  I built the "circuit board" from a piece of acrylic plexiglass, with holes drilled for the through-hole components (555, A4988, and 7805 regulator), and passive components wired point-to-point underneath.  I'm proud to say, it worked at first power-up, which is not always the case! I have not yet built the spindle to attach to the shaft and hold the pickup bobbin; so far, I've just been testing the raw motor unit to make sure it can run for hours at a consistent slow speed, which it seems to do fine.  The one pro...

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...