The Artec PAMP3 is an active circuit designed for use with piezo bridges on electric guitars. This could be used in conjunction with a piezo to add an electric output to a Jazz guitar that does not have pickups.
The PAMP3 has a 3 band EQ, with three potentiometers individually controlling bass, middle and treble. It has a gain control and a volume control. Attached to it is an output jack and a 9v battery clip.
This is an all in one solution to adding a piezo acoustic tone to your electric guitar (just add the piezo).
Potentiometer shaft diameter: 9mm