| This simple circuit can color the
sound coming from your audio system. Clocking for the circuit is provided by an oscillator
built from one quarter of a 4093 quad NAND Schmitt trigger. With the component values
shown, it will run at about 5 Hz. The clock frequency is fed to the gain control, pin 8,
of an LM386 amplifier. Tremolo is produced by varying the amplifier gain. A trimmer
potentiometer can be put in series with R1, to easily experiment with different rates. To
experiment, make R1 about 100-K ohm and use a 1-M ohm trimmer. That allows frequencies
from about 2 to 20 Hz to pass. Resistor R2 is the depth control. It controls the degree of
tremolo. To adjust, put a trimmer in series with R2. Make R2 a 5-K ohm unit and use a 50-K
ohm trimmer. Since the tremolo clock uses the gain-control pin of the amplifier, change
the value of capacitor C4 in order to change the gain of the amplifier. Make C4 larger to
increase the gain or smaller to decrease it. But, don't go any lower than 0.1 mF because
you'll be cutting into the bottom-end frequency response. |