I first started building homemade stringed instruments, I used a piezoelectric buzzer from Radio Shack (273-073A) as a pickup
for electrifying the instrument. A piezo is cheap and simple—you carefully crack open the edges of
the black plastic case and gently lever out the thin, quarter-sized piezoelectric element. Solder the two
wires to the wires of a short length of two-conductor shielded cable, and solder the wires at the other end of the cable (including
the shielding) to a ¼" phono jack (Radio Shack 274-0252). Install the piezo element inside
the cigar box guitar or diddley bow under the bridge, and the phono jack into the body of your instrument and you are
ready to rock.
While cheap and simple, a piezo transducer has some down-sides:
it has a low signal output compared to an electromagnetic pickup, so it needs preamplification to match up with a guitar
amp. Volume control is done as a part of the preamp stage. Furthermore, a piezo picks
up a lot of handling noise—it is responding to the vibration of the whole instrument, not just the strings—therefore,
it can go into uncontrollable feedback in high volume situations. Finally, a piezo sounds thin—it's
okay to reinforce an acoustic sound, but not nearly as authoritative as an electromagnetic pickup for rock and blues applications.
If you want to crank it up to sound like you really DO have possession over Judgment Day, an electromagnetic pickup
is the better choice.
I use a plastic sewing machine bobbin electromagnetic
pickup for my diddley bow, and used my wife's sewing machine to wind the magnet wire (42 gauge single build) onto the bobbin.
Note that Singer sells several different sizes of plastic sewing machine bobbins--not all of them will fit the magnet.
Get the magnets first, for example at www.forcefield.com, and then shop for the bobbins. Wind several at once, because the
wire is so fragile that it is easy to break a few before you get it mounted and wired up to a potentiometer. At least if you
are as clumsy as I am.
The assembly is then potted in a mixture of paraffin and beeswax. The idea is that
this will reduce microphonics (the sounds made when the wires in the pickup pick up vibrations from the guitar/sound system
instead of just passing electrons in response to the changes in magnetic field made by the string. The pickups were
soaked in 80% (by weight) paraffin (from the grocery store--it is used for canning), 20% (by weight) beeswax (from the craft
shop--it is used to make candles).
Caution: The vapors this
stuff gives off when hot are highly flammable (this is why a candle burns), and it is entirely possible to set your kitchen
on fire if you make a mistake.
Don't call me if you set your kitchen on fire.
the following to try to avoid this potential problem: I bought an empty one quart paint can and put the solid paraffin and
solid beeswax in it. I heated up a pot of water on the stove, shut off the heat when it got to the simmer, and then placed
the can of wax in the pot. Once the wax had melted so I could put the lid on the can, I did so. Every so often, I would stir
the melting wax with a wooden paint stirrer. If the water cooled off before the wax was fully melted, I took the can out of
the water, kept it covered, and then heated the water again. Then I shut the fire off, put the covered can of wax into the
pot, and stirred it until the wax was thoroughly melted and mixed.
One important thing is that the fire is always
OFF when the can of wax is uncovered. I would suggest doing this when you have plenty of ventilation, and don't smoke when
the lid is off the can of hot wax.
I then placed the wound bobbins on a loop of coat-hanger wire that could dip
into the wax and let them sit in the wax until bubbles stopped coming out of the windings. This indicates the wax has penetrated
I then pulled the bobbins out of the liquid wax, and let them air-cool over a paper towel. I labeled
and covered the can of wax. I cut some cloth tape (for bandages) to fit etween the sides of the bobbin and wrapped the coils
with the tape to protect them from damage. I cleaned the wax out of the hole in the bobbin, and then inserted the magnet,
and then mounted the pickups for wiring.
I drilled two small holes in a piece of very thin plywood for the leads
to go through and mounted the bobbin using hot glue (passing the magnet wire leads through the holes). I then cut off
two brass escutcheon pins and mounted them on the underside of the board to use as soldering posts and (after sanding the
coating off the ends of the wire), soldered the leads to the escutcheon pins. Then I wired in
the guitar volume pot and
shielded cable, again using the escutcheon pins as soldering posts. The board was mounted on another piece of wood to hide
most of the wiring. I realized the bobbin was pretty exposed, so I made a protective wood ring around it so it can't get knocked
off easily. It looks like it is--kind of hackwired, but it works okay. The whole thing is screwed onto another block
of wood, and held on the diddley bow by a double rubber band.
The sound from a broom-wire string (because there
is a lot of metal moving there) is thunderous.
I need to make some more of these assemblies, and will take pictures
and write up the procedure as I make a new batch. This will be posted on this page.