Catalyst Audio - Mig VCA

Catalyst Audio + Electroserf's MIG VCA is a fully analog voltage-controlled amplifier built around a 1J24b subminiature vacuum tube. It can behave like a normal VCA, but the surrounding controls let you lean into the tube’s less tidy habits: bias shifts, saturation, feedback, thumps and folding. Catalyst call it a VCA and a general destructive sound source, which is fair: signals tend to come out changed. Init Gain sets the tube's amplification, while Linearity adjusts its bias, sweeping from an under-biased, high-end-heavy edge through a roughly linear setting around noon and on into smoother, saturated flavours as you overbias it.

A handful of controls push it well past clean duty. Resonance feeds the output back into the tube for extra nonlinearity and distortion, with a switch to set its frequency. The Fold switch drops an amplitude-controlled folding stage onto the output. And the Thump knob handles the DC offset tubes naturally produce — dial it in to smooth the click, or leave it off and keep that percussive thump as a feature. There's also a Y input for sending a second audio signal into the tube's gain, which is your route to amplitude modulation and pseudo-ringmod sounds.

Two outputs round out the repertoire: the main output, and a Diff output that subtracts the main from the dry input — literally the difference the VCA is making. A good pick when you want a VCA that also colours, drives and occasionally roughs up whatever runs through it.

Features:

• Analog vacuum tube voltage-controlled amplifier built around the 1J24b
• Doubles as a character and distortion source
• Init Gain for the tube's amplification level
• Linearity control re-biases the tube: edgy/high-end → linear → saturated
• Resonance feedback into the tube, with a frequency switch
• Amplitude-controlled Fold stage
• Thump control over the DC-blocking filter (tame it or keep the percussive thump)
• Y input for amplitude modulation and pseudo-ringmod
• Main output plus Diff output (input minus VCA output)
• CV inputs with attenuverters for Gain and Linearity
• NOS Cold War-era Soviet pentode tubes
• 100% analog