Alongside other projects, I am busy with a stradella-type chord keyboard based loosely around my MIDI-synthesizer work (see connectable.org.uk). The idea is (at the moment) to provide a flip-over keypad which will then sit over the guitar fretboard. As well as being able to play a wide selection of chords, each with a single key-press, the voicing for the chord-production (which will be MIDI) can be controlled with the right hand playing on the strings. The work is far from finished, but it involves the use of a pickup for each string, and I’ve used a simple technique in the manufacture of the pickups which may be of interest to those who have read, or currently are reading, the article(s) on High Quality Guitar Pickups On a Shoe-string.
|A Bifilar-wound low-inductance string pickup made using a plastic sewing-machine spool machine and 2 neodymium magnets.|
|The spool on the left is as bought from sewing-machine accessory suppliers. It contains a convenient slot to anchor the winding into. Look carefully and you can see I’ve reduced the cheek diameter to the ridge on the original spool. I did this (carefully) on a lathe, but ad-hoc measures involving a small grinding wheel should also give satisfactory results. Dimensions are as follows:
There are plenty of suppliers of magnets on the web, one suggestion is: http://www.first4magnets.com/bar–rod-magnets-1-c.asp
I fitted 2 magnets, leaving one end slightly-proud of the former. A single-rod 1/2 inch long would be equally as good. Using 26swg wire, a total coil resistance of 2.3 ohms resulted. This works well with the balanced amplifier in the main topic.
|Every guitar is different, and the finished coil dimensions meant I would have to stagger the coils across the strings. You should ascertain what the finished coil diameter should be for your guitar and maybe reduce the cheek diameter before making 6 of these!|
|This crude, but effective setup enables easy winding of biliar coils. Two reels of the same diameter wire are mounted on the 6mm bar in the foreground. The coil former is mounted on a 6mm screw and held in the chuck of the hand-drill. After anchoring each wire firmly in the spool slot, the hand-drill is turned clock-wise whilst guiding the 2 wires using the fingers of your left hand. (folks that are left-handed should build a mirror-image of the arrangement!) For counting turns (I don’t always bother) I’ve mounted a burglar-alarm type reed-switch on a strip of plastic, and the small neodymium magnet attached, reliably produces switch closures for a counter as the drill shaft revolves. The hand-drill is easily detached from the terry-clips for use elsewhere if required.|