I was inspired by the youtube video on the right to electrify my Cigarbox guitar. I had done a project in the past where I wired a piezoelectric buzzer directly into some PC speakers but it never did sound that great. I did some searching on the web and found that's Colin's circuit was a basic version and that it could be improved upon namely by adding some Zener diodes to protect the FET from voltage spikes.
Collin's Lab -- DIY Contact Mic (embedded on this page)
- MPF102 Field Effect Transistor (Radio Shack 500 colones)
- Piezoelectric buzzer -- taken from an old calculator
- Electrolytic capacitors -- 4.7uF and 10uF
- Resistors: 3.3M, 560 (470*), 1.5K, 220K
- 2 x 5.1v Zener Diodes
- 9V battery
- 1/4" phono jack
- Small protoboard
Breadboarding the circuit
I first setup the circuit on a breadboard to test and to bias the MPF102 according to these instructions:
*For my particular MPF102 I found that 470 ohms gave me a better reading and switched that for the 560 ohm.
- Add an ON/OFF switch
- Find a phono jack with a larger "beak" that can install in a 1/4" wooden wall
- Change the 220k ohm resistor for a potentiometer to vary the gain