Tremolo Amplifier Circuit

The amplifier modulates the audio input signal at an infrasonic frequency (usually 5-15Hz). The National Corporation LM389 integrated circuit used has an internal array containing three transistors and a power amplifier. These transistors form a differential pair and an active current source tail. The output of this differential amplifier is proportional to the product of the two input signals. The gain control potentiometer is used to adjust the required tremolo intensity. The R and C networks between the stages form a 160HZ high-pass filter, requiring the tremolo frequency to be lower than 160HZ.