The tremolo effect is generated by a repeating volume change at a rate usually between 1 and 15Hz. The timer produces a low frequency square wave that is smoothed by a simple rc integrator. This varying signal modulates the signal input from the instrument. Transistor Tl is used as a voltage controlled resistor. The output of the circuit is connected in parallel to the output of the instrument.
Potentiometer P1 provides depth control by adjusting the amplitude of the modulating waveform applied to the instrument. The rate contrul frequency is set by potentiometer P2.