Tremolo is an old school effect, and can be heard on many old 60’s surf songs and some more recent ones over the years. An opto based device is used to modulate the volume of the guitar signal. This opto device is controlled by a low frequency oscillator which can be set to square wave or triangle / sine wave. These two modes sound quite different with square wave being more choppy or stuttering while triangle / sine wave produces gradual and smooth changes.
When the effect is on, the LED goes on and off with the tremolo speed allowing easy setting of the tremolo speed by eye.
With a low setting on the Depth control and a slow Rate setting, the effect is almost like a chorus.