A pickup, or transducer, converts mechanical energy into an electrical signal that can be amplified. One type of transducer, known as a piezo pickup, uses changes in pressure applied to a crystal element to produce an electric signal. This type of pickup is resistant to body feedback and works well with instruments like the violin. A simple way to make a piezo transducer is to attach an output cable to a piezo buzzer disc sold in electronics supply stores.
Remove the buzzer's plastic casing with a knife. Be careful not to damage the metal and ceramic element inside. The two layers of the element must be in contact in order to produce a signal.
Carefully pry the element from the backing material. It is held in place with a small amount of glue, so using a knife is advisable.
Make a note of the point at which each wire was attached. Remove the black and red lead wires using a soldering iron to loosen the solder. Leave the two solder points on the element. On the Radio Shack buzzer, the point to which the red lead was attached is the signal connection. The black wire contact point is the ground connection.
If necessary, use a wire cutter or knife to trim away a short length of insulation of the audio cable wires for soldering. Solder a short length of the signal wire to the signal contact on the element. Repeat this step with the ground wire.
Solder the signal and ground wires to the proper contact points on an output jack.
Test by plugging the pickup into an instrument amplifier. If no sound is produced, examine for loose connections.
Apply a small amount of poster putty or double-sided tape to the bottom or along the edges of the pickup.
Place the transducer near or on the instrument's bridge, where the energy from a string's vibration is transmitted to the body. Experiment with placement on various points of the body.
For best results, piezo pickups should be used with an electric signal buffer before being amplified. The element can be used as is, or it can be trimmed with tin snips to the desired shape and size, provided that the layers of the element are not separated. If multiple strips are made, new contact points must be made for the lead and ground wires. For long term attachment, a Carpenter jack is highly recommended. This 1/4-inch jack is attached to a bracket that fastens to the side of the instrument like a chin rest.
When using electric soldering irons, observe all safety precautions.