AJH Synth Matrix VCF

This amazing multimode filter and VCA offers sixteen different filter types, and two different resonance models on each, totalling an incredible thirty two assorted resonant filters to choose from. We've also included manual and CV control of filter type selection, along with 16 LED's that give a clear visual indication of which filter type is currently selected.

The filter core circuitry is based on that of the rare and highly sought after Oberheim Matrix 12 synthesiser, and of course has an all analogue signal path. The Matrix 12 VCF originally offered fifteen filter types, however we have expanded this to 16 with the addition of AP4, a full four pole all pass phaser mode.

We have added a unique P-Vox resonance distortion and overdrive circuit that changes the character of the resonance completely, and can force all of the filter modes into self oscillation. This effectively doubles the filter variants and hugely broadens what is already a very impressive sound pallet.

Other features include an inbuilt VCA with Input and Output Level controls, a Peak level LED, CV control of resonance, and of course the legendary AJHSynth build quality.

Module Width: 14hp

Module Depth: 29mm (Including power lead)

Current Usage: 56mA Positive, 36mA Negative

Sixteen distinct filter modes to choose from

Here's a list of the different filter modes that are available:

1 - Four Pole Band Pass

2 - Three Pole High Pass combined with One Pole Low Pass

3 - Three Pole All Pass combined with One Pole Low Pass

4 - Two Pole Notch combined with One Pole Low Pass

5 - Two Pole Low Pass

6 - Four Pole All Pass (Phaser)

7 - Four Pole Low Pass

8 - Two Pole Band Pass

9 - Two Pole High Pass combined with One Pole Low Pass

10 - Three Pole High Pass

11 - Three Pole All Pass

12 - Two Pole Notch

13 - One Pole Low Pass

14 - Two Pole High Pass

15 - Three Pole Low Pass

16 - One Pole High Pass

All of the above filter types can be further altered by switching in P-Vox mode, this doubles the list up to thirty two different filter variants!

P-VOX MODE

Transforming the resonant character of every filter type

This magical switch completely transforms the resonance of the filter core by overdriving it in a similar fashion to the filter from the Soviet Polivoks synthesiser, which was renowned for it's powerful, aggressive character.

In common with the Oberheim Matrix 12 VCF, some of the sixteen filter types will not normally go into self-oscillation, however when we switch on P-Vox mode all sixteen filter types can be forced into self-oscillation at higher resonance settings. But that isn't the only change, the self-oscillation waveform is not the usual sine waveform, it is a rather more interesting and harmonically rich waveform that varies according to the filter type chosen - generally Low Pass modes produce the nearest to regular sine waves, whereas other filter types can produce very much more complex waveforms as can be seen in the diagrams below. It does not require any audio input for this, it can be a stand alone oscillator. Most of the filter types will track 1V/Oct reasonably well over a three to five octave range, so it can be used as a VCO with a few interesting waveshapes!

Of course, P-Vox mode isn't just useful for self-oscillation, it adds lots of character to any audio signal as P-Vox resonance is switched in.

The MiniMod VCA is arguably the best sounding VCA available in Eurorack, as it captures the beautiful second harmonic distortion signature of the early Model D synthesiser, so we would always use this in a patch if we have unlimited modules available - for instance if using our RadioPhonic monster modular system. However, sometimes we just need a VCA that does what it says on the tin, without adding it's own sound signature to the signal path, and the inbuilt VCA on the Matrix VCF serves this purpose admirably. It is hard wired to the output of the Matrix VCF and is very simple to use.

If we don't patch anything into the VCA jack then the Output level control functions as a manual volume control, because the VCA jack’s internal switch is normalled internally to +5V. However, if we patch a CV (for example from an Envelope generator or an LFO) to the VCA jack then this external control voltage is used to control the level of the inbuilt VCA, and now the Output Level control will act as an attenuator for the incoming CV signal. This is very useful as it still allows the overall output level to be controlled - we can adjust the output level so that the Peak LED indicator is just starting to flash, knowing that we have set the output at optimum signal level of 10V p/p so that we don't push the output stage into clipping distortion, or overload any Eurorack modules that may be connected to the Matrix VCF Output.