The AJH Synth MiniMod VCF is a recreation of the 24dB/Oct low-pass transistor ladder filter used in the classic Moog Model D synthesizer. It features a three-channel input mixer, dedicated filter cutoff knob, and both 1/3” and 2/3” CV ins that faithfully emulate the original Model D’s VCF switches. There’s also a variable CV input offering additional modulation possibilities.
In addition to a manual Emphasis control, there is now a vactrol-controlled CV input for voltage controlled resonance. Since the input features a vactrol, it can reach audio rates, allowing the filter to self-oscillate for use as a sine wave oscillator.
This is the SILVER version of the MiniMod VCF.
MiniMod VCF Features
Eurorack Replica of the 24db/octave Low Pass Transistor Ladder Filter used in the early Moog Model D Synthesizer
3 Channel Input Mixer
1 Filter Signal Output
1V/OCT Input: Changes the filter cutoff at the rate of 1V per Octave, or if the filter is in full self-oscillation (Emphasis Control fully CW) it will control the pitch of the resulting sine wave at the rate of 1V/OCT (When compared to the Model D this emulates having “Keyboard Control” switches 1 and 2 “ON”)
Frequency CV Input
1/3 CV Input: Changes the filter cutoff at the rate of 333mV per Octave (When compared to the Model D this is the equivalent of having “Keyboard Control” switch 1 “ON” and switch 2 “OFF”)
2/3 CV Input: Changes the filter cutoff at the rate of 666mV per Octave (When compared to the Model D this is the equivalent of having “Keyboard Control” switch 1 “OFF” and switch 2 “ON”)
Emphasis CV Input: ±5V
Emphasis CV Input Level Control: 0% to 100% (Manual Emphasis Level Control is still active and acts as an offset control)
Emphasis Level Control (Resonance Level Control): Self-Oscillates between positions 8 and 10
Filter Cutoff Control
Frequency CV Level Control: 0% to 130% (Greater range than the 1V/OCT Input so over-modulation effects are possible)
The first patch in this video is a bass sound with two saw oscillators overdriving the Transistor Ladder Filter. The second patch uses the shark tooth waves as well sub bass waveforms generated by the Ring SM module, a delay makes the sequence sound more complex and a second MiniMod Filter is used on the delay repeats. In the third patch one oscillator is synched to the other and the delay is still used.
The AJH MiniMod Eurorack modules bring the great sound of the MiniMoog Model D discrete circuitry into the Eurorack format with a look reminiscent of large format Moog Modulars.