AJH Synth Matrix VCF

Name: Matrix VCF
Brand: AJH Synth

Sixteen-response analogue filter and VCA

14 HP Eurorack module

An analogue multimode filter and VCA based on the Oberheim Matrix 12 filter core, offering sixteen filter responses with two resonance models for each.

Features

MODE selects sixteen filter responses, from four-pole band-pass fully counterclockwise to one-pole high-pass fully clockwise. A dedicated LED indicates the selected response during manual or CV selection.
Patching MODE CV makes MODE an attenuator for external filter selection. Fully clockwise, 0 to +5V covers the selection range. Remember to avoid negative MODE CV voltages because they can cause erratic behavior.
Cutoff Frequency moves the filter passband. FCV provides external cutoff modulation, with its depth attenuated by FCV Level.
V/OCT controls cutoff at one volt per octave. During self-oscillation, it supports pitched oscillator use over approximately three to five octaves.
The additional cutoff inputs have fixed sensitivities: 1/3 is approximately three volts per octave; 2/3 is approximately two volts per octave. Control modulation depth externally when using these inputs.
IN expects modular audio around 10V peak-to-peak. IN LEV attenuates this signal and balances external audio against self-oscillation. Some filter types may not attenuate fully to silence at low cutoff settings.
RES increases resonance clockwise. When RES CV is patched, RES attenuates the incoming CV; fully clockwise gives a 0 to +5V control range. Negative resonance CV is treated as zero.
With VCA unpatched, its +5V normalization holds the VCA open and OUT LEV acts as a manual volume control. Patching VCA makes OUT LEV an attenuator for amplitude CV. Fully clockwise gives a 0 to +5V range; negative CV is treated as zero.
Peak Level flashes or stays red above 10V peak-to-peak. Filter response, cutoff, and resonance can substantially change output level; use OUT LEV with this indicator to balance signal level and avoid overloading downstream modules.
P-Vox adds resonance distortion to external audio and supports self-oscillation without an audio input. Its oscillation waveform depends on the filter response; low-pass responses produce waveforms closest to sine waves.
Filter selection supports audio-rate modulation. Remember that switching responses changes signal phase and can produce an audible click from a sudden DC offset. For sequenced changes, an envelope patched to VCA can mute the signal around the switch.

Controls & Jacks (33)

AP 4 Selected— Illuminates when mode 6, four-pole all-pass phaser, is selected.
RES— Increases resonance clockwise. Some responses self-oscillate at high settings in normal operation; P-Vox enables self-oscillation in all six
LP 4 Selected— Illuminates when mode 7, four-pole low-pass, is selected.
IN LEV— Attenuates audio arriving at IN, allowing external audio to be balanced against self-oscillation. Some filter types may not attenuate fully
LP 1 Selected— Illuminates when mode 13, one-pole low-pass, is selected.
MODE— Manually selects one of sixteen filter responses, from mode 1, four-pole band-pass, fully counterclockwise to mode 16, one-pole high-pass, f
HP 3 Selected— Illuminates when mode 10, three-pole high-pass, is selected.
NT 2 Selected— Illuminates when mode 12, two-pole notch, is selected.
RES CV— External resonance control, attenuated by RES. With RES fully clockwise, the control range is 0 to +5V; negative voltages are treated as zer
HP 2 Selected— Illuminates when mode 14, two-pole high-pass, is selected.
IN— Audio input to the filter, expecting modular levels of approximately 10V peak-to-peak; its level is controlled by IN LEV.
LP 2 Selected— Illuminates when mode 5, two-pole low-pass, is selected.
Cutoff Frequency— Sets the filter cutoff frequency and moves its passband.
AP 3 Selected— Illuminates when mode 11, three-pole all-pass, is selected.
OUT— Filtered audio output through the built-in VCA, with level determined by OUT LEV and any patched VCA CV. Also carries the filter's self-osci
BP 2 Selected— Illuminates when mode 8, two-pole band-pass, is selected.
OUT LEV— Sets the audio output level. With VCA unpatched, its +5V normalization lets this knob act as a manual volume control; use the Peak Level ind
FCV Level— Attenuates cutoff modulation received at the FCV input.
1/3— Additional cutoff modulation input with fixed sensitivity of approximately three volts per octave, or one volt per 0.33 octaves.
NT 2+LP 1 Selected— Illuminates when mode 4, two-pole notch combined with one-pole low-pass, is selected.
V/OCT— Controls cutoff frequency at one volt per octave. During self-oscillation, supports pitched oscillator operation over approximately three to
HP 2+LP 1 Selected— Illuminates when mode 9, two-pole high-pass combined with one-pole low-pass, is selected.
LP 3 Selected— Illuminates when mode 15, three-pole low-pass, is selected.
2/3— Additional cutoff modulation input with fixed sensitivity of approximately two volts per octave, or one volt per 0.66 octaves.
VCA— Controls the output VCA. Normalled to +5V to hold the VCA open when unpatched; patching a cable makes OUT LEV an attenuator for the incoming
Res O/Drive— Up selects normal Oberheim Matrix 12-style resonance. Down engages P-Vox resonance overdrive, adding aggressive harmonic distortion and enab
AP 3+LP 1 Selected— Illuminates when mode 3, three-pole all-pass combined with one-pole low-pass, is selected.
HP 1 Selected— Illuminates when mode 16, one-pole high-pass, is selected.
FCV— Cutoff frequency modulation input attenuated by the Freq CV Level control.
HP 3+LP 1 Selected— Illuminates when mode 2, three-pole high-pass combined with one-pole low-pass, is selected.
MODE CV— Selects the filter response using external CV. With MODE fully clockwise, 0 to +5V covers all sixteen modes; MODE attenuates the incoming vo
Peak Level— Flashes or remains red when the output exceeds 10V peak-to-peak, providing a reference for output-level adjustment.
BP 4 Selected— Illuminates when mode 1, four-pole band-pass, is selected manually or by MODE CV.

How-To Guides

Patch a synth voice
Patch cutoff modulation
Use P-Vox as an oscillator
Smooth sequenced filter changes
Set the VCA output level
Scale a 0 to +10V mode CV
Patch external resonance control

Explore the interactive Matrix VCF panel on BleepDex — tap any control to learn what it does.