The Gristleizer Modulator presents another key component of the Gristleizer in a Eurorack module - its JFET-controlled voltage-controlled amplifier. Whilst originally controlled by the Gristleizer's oscillator to achieve tremolo (or amplitude modulation) effects, the TG4 can be controlled by any control source available in a Eurorack system and, therefore, be used as a conventional VCA with some added features.

The Bias control sets the initial control point of the amplitude modulation, whilst a control voltage attenu-verter for CV2 allows for full control over how the amplitude is modulated. On top of this, the TG4 features a Dirt control, which allows the user to alter the behaviour of the JFET stage. At zero Dirt, the Modulator offers a super-clean VCA, whilst at maximum Dirt, waveforms become drastically mutated, at times beyond recognition. With the Dirt setting at 12 o'clock, the Modulator behaves exactly like the original VCA circuit of the Guitar Effects Pedal design. Also note that the JFET tends to exhibit second-harmonic distortion, similar to that of vacuum-tube amplifiers. Therefore, the TG4 presents not just a VCA, but also a module for adding distortion and character to audio signals.