The StompLFO Optical Tremolo is a guitar pedal that uses a vactrol to produce volume changes. The vactrol operates as a voltage divider, with the LED’s on and off states controlling the resistance and thus the signal level. The StompLFO’s output pin can provide up to 20mA to power the LED, with a forward voltage of 2.5V at 16mA current. The resistance of the vactrol can be tested using different resistor values, with results varying depending on the LED current.

The StompLFO control circuit requires solid voltages for its four CV inputs. It features pots for Rate and Depth, with the Offset CV tied to 0V for modulation from the top down. The Waveform CV can be adjusted according to preference, with options including Triangle, Sine, and Square waves. The Rate pot can be adjusted to limit the range or cover the full range from 0.05Hz to 25Hz.

The audio path of the pedal includes an input buffer with gain, a vactrol-controlled-voltage-divider, and an output buffer with volume control and output protection. The input buffer provides a high impedance for any source plugged in and has some gain available. The gain resistors are chosen with moderate values to balance noise generation and current usage. The pedal also features a bicolour common-cathode LED for bypass and LFO indication, flashing at the LFO rate and changing colour to indicate whether the effect is on or off.

Summary created by AI and may not be accurate. See original source.