The FilterFX guitar pedal is a unique device that uses the Druid STOMPLFO to control a 12dB/oct state variable filter. This filter design offers highpass, bandpass, and lowpass outputs, providing a wide range of effects. The LFO offers eight waveforms, including two random waveforms for unique sound effects. The pedal also allows for the addition of an expression pedal, enabling the filter to be used like a wah pedal. The expression pedal can be used in conjunction with the LFO modulation or by itself. Additionally, the pedal features a Sync input for the LFO, allowing it to sync with an external clock from a sequencer, drum machine, or another LFO.

The SVF filter is controlled by a Druid STOMPLFO chip which provides eight waveforms, including two unusual random waves for less repetitive filtering effects. The chip also offers tap tempo to set the speed and a provision for a Sync input which can accept clock pulse from other devices to keep the FilterFX in time with other gear. The knobs on the pedal include Rate, Waveform, and LFO Depth, all of which are variable using 0-5V control voltages.

The schematic of the FilterFX is straightforward and will be familiar to those who have studied state-variable filters. The input features a unity-gain buffer IC1.2 to provide good input impedance and prevent tone-suck. IC1.1 acts as a differential mixer, mixing the input with the two feedback signals from the next two stages. IC2.1 and IC2.2 are op-amp integrator stages, with their frequency controlled by the two vactrols. The Mode switch selects between lowpass, bandpass, and highpass outputs available from the two integrators and the mixer stage. The second page of the schematic is dedicated to the LFO and power circuit, with standard power circuitry for a stompbox and a stable 5V supply for the STOMPLFO processor.

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