This is a ring modulator, the same kind of effect they used to make the Dalek voice in the Dr Who show in the 60s. It has a triangle oscillator inside - there's a knob on the spine that sets the frequency. This oscillator and your input signal (voice, guitar, keyboard etc) are fed into a simple circuit made of two small transformers and four diodes, which does a multiplication and outputs the sum and difference of the input frequencies. The result is a metallic-sounding combination of the two signals. It really mangles your input and creates an instant "electronic music" effect. If you plug in a guitar it sounds like your strings are rubber bands. If you turn the onboard oscillator frequency way up you just get these little crispy squirts of high pitches.
Controls (bottom to top):
Input, Bypass, Gain High/Low, Frequency, Output.
Set gain switch to high (upwards) for microphone or guitar input, down for line level, eg. keyboard, laptop etc.
Powered by 9V battery or 9V DC centre-negative power supply.
Circuit: Passive Ring Modulator. Designed by Pat Kraus, built by Nich Cunningham
What is a Ring Modulator?