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The perennial innovators at Pigtronix have delivered the Resotron, a resonant envelope filter that gives you all the tools to transform your guitar into a full-blown ’70s synth.

Inside the Resotron, you’ll find a filter based on the legendary Solid State Micro SSM2040 chip, the same one found in classic synths like the Sequential Circuits Prophet 5 and the Octave Cat.

However, while the Resotron gives you every filter option you can think of, it’s engineered to operate with a stringed instrument; the key difference. Thus, it’s voiced to react with your guitar, rather than be a synth circuit dumped in a pedal enclosure. It’s downright revolutionary and will be on display at the NAMM show. – Nicholas Kula

Pigtronix Resotron is an analog filter that brings the sound of 70’s keyboard synthesizers to the world of envelope pedals for guitar, bass and beyond. The filter at the heart of the Resotron is based on the SSM2040 chip found in the legendary Prophet 5 and Octave CAT synthesizers. This 24db/octave, state-variable filter provides the full gamut of familiar envelope filter sounds with UP and DOWN sweeping modes, and a sensitivity control to dial in the response of the effect based on how hard you play. In addition to these vintage-correct filter tones, the Resotron pushes the envelope pedal concept to a whole new level by using an analog pitch-tracking system to move the cutoff frequency of the filter up and down. The pitch-following filter effect found in the Resotron moves around based on the notes you play instead of how hard you play. The attack time and rate of filter motion can be adjusted—using the GLIDE knob—to dial in how long it takes for the cutoff to travel between pitches.

The Resotron has the ability to operate in Low Pass, Band Pass or High Pass modes. Each of these filter voices has a distinctive character that can be manipulated by adjusting the PEAK knob, progressively feeding the filter back upon itself to increase the resonance (or “Q”) of the filter, right up to the point of self-oscillation. A push-button OSCILLATE function allows you to go even further—turning the Resotron into an analog synthesizer pedal that follows both the pitch and dynamics of your playing. The synthesizer sounds created by the Resotron can be radically altered by switching between the LPF, BPF and HPF modes. This allows users to access waveforms that range from subtle voice emulations to bombastic, aggressive lead sounds, as well as ultra-smooth sub bass tones.

Before the pedal’s input signal hits the Resotron’s filter, it passes through an optical compression stage derived from the Pigtronix Philosopher’s Tone pedal. The increased volume and punch from this compressor can then be mixed into the audio signal using the BLEND control—without affecting the SENSITIVITY of the envelope. Resotron accepts active CV and passive TRS expression pedal inputs for foot-controlled filter sweeps and outboard modulation, which is mixed in parallel with the on-board pitch-following and amplitude tracking systems.


24db/oct filter based on the SSM2040 chip
Low Pass, Band Pass & High Pass Filter options
Velocity controlled UP & DOWN envelope modes
Pitch-following envelope function with variable GLIDE
BLEND control mixes in Philosopher’s Tone compression
Expression pedal / 0-5V CV input modulates CUTOFF
OSCILLATE mode for monophonic synth sounds
Sidechain TRIGGER input for external audio
Hardwired true bypass switching
18VDC power supply included
100% analog design
Circuit design by Nick Cote
Sound design by David Koltai