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Cigarbox guitar Pre-Amp

Introduction

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.

References

Collin's Lab -- DIY Contact Mic (embedded on this page)

Schematic


Materials

  • 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.

Construction

TO DO
- 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

Test/Demo


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