Matrix VCF: Versatile Eurorack Multimode Filter and VCA

Introducing the AJHSynth Matrix VCF

The AJHSynth Matrix VCF is a highly versatile Eurorack multimode filter and VCA module, offering an extensive range of sound-shaping options. Based on the rare Oberheim Matrix 12 synthesiser’s filter core, this module features an all-analogue signal path and expands the original fifteen filter types to sixteen by adding a four-pole all-pass phaser mode. With two resonance models available for each filter type, users can select from a total of thirty-two resonant filter variations.

Extensive Filter Modes and Resonance Options

The Matrix VCF includes a wide variety of filter modes such as low pass, band pass, high pass, notch, and complex combination filters. The addition of the unique P-Vox resonance distortion and overdrive circuit, inspired by the Soviet Polivoks synthesiser, allows all filter types to be driven into self-oscillation with harmonically rich waveforms. This feature significantly broadens the sonic palette, enabling sounds ranging from warm and fat to aggressive and distorted.

Filter Modes Available

Four Pole Band Pass
Three Pole High Pass combined with One Pole Low Pass
Three Pole All Pass combined with One Pole Low Pass
Two Pole Notch combined with One Pole Low Pass
Two Pole Low Pass
Four Pole All Pass (Phaser)
Four Pole Low Pass
Two Pole Band Pass
Two Pole High Pass combined with One Pole Low Pass
Three Pole High Pass
Three Pole All Pass
Two Pole Notch
One Pole Low Pass
Two Pole High Pass
Three Pole Low Pass
One Pole High Pass

Each of these can be further altered by engaging the P-Vox mode, doubling the filter variants to thirty-two.

Control and Interface Features

The Matrix VCF offers both manual and CV control over filter type selection, with sixteen LEDs providing clear visual feedback of the current filter mode. The module includes controls for cutoff frequency, resonance level, input and output audio levels, and multiple CV inputs for frequency and resonance modulation. The inbuilt VCA is hardwired to the output and can be controlled via an external CV or manually adjusted, simplifying patch setups.

Key Controls and Inputs

Cutoff Frequency control knob
Mode knob and Mode CV input for filter type selection
Audio Input Level attenuator
1V/Oct, 1/3 Freq CV, 2/3 Freq CV inputs for frequency control
Resonance Level control and RES CV input
Resonance Overdrive (P-Vox) switch
VCA CV input and Output Level control
Audio Output jack

Additional Features and Usage Notes

The Matrix VCF can be used as a standalone oscillator due to its self-oscillation capabilities and 1V/Oct tracking over three to five octaves. The module’s design emphasizes an intuitive user interface, avoiding complexity while providing extensive functionality. Users should note that switching filter modes can cause audible clicks due to phase changes; however, this tradeoff allows for audio-rate modulation of filter types, enabling creative effects such as “Matrix Sync.” A suggested workaround involves using an envelope generator to mute the signal briefly during mode changes.