AJH Synth MiniMod VCF - Manual

VCF User Guide
Thank you for purchasing the AJH Synth MiniMod VCF module, which like all AJH Synth Modules,
has been designed and handbuilt in the UK from the very highest quality components. We hope
that it will help and inspire you towards creating some great music and soundscapes!
The MiniMod VCF is a very faithful replica of the four pole 24db/octave low pass filter used in the
early Model D synthesiser. By using fully matched discrete ladder transistors along with audio-
phile grade capacitors and operational amplifiers in the audio signal path, it captures the vintage
sound and vibe of this epic filter and combines it with the versatility of the Eurorack modular
format.
The front panel provides a three channel input mixer and a large filter cutoff control, along with
1/3 and 2/3 CV inputs to emulate the action of the original VCF keyboard switches. There is also a
variable Exponential CV input which is about 30% more sensitive than the 1v/oct input, which
allows some nice over modulation effects.
Added features include Voltage Controlled Emphasis (Resonance) which uses a Vactrol as the
control element. This approach was chosen because it is a purely resistive element and impor-
tantly has no impact on the vintage sound of the filter. The fast acting Vactrol chosen allows
modulation speeds up into the audio range. The filter will of course self-resonate and act as a sine
wave oscillator too.
An overdrive facility can be selected using the onboard jumper which allows the input to the filter
core to be substantially overdriven - great for adding a bit of extra dirt to the sound!
Module width is 14 HP of Eurorack space and it is compatible with standard Eurorack cases. The
height of the panel is 128.5mm, and depth is 26mm . There are four mounting holes at the
corners of the module and we provide 4 of M3 rack fixing screws, along with a Eurorack compat-
ible power cable. Current consumption is 45mA from the +12V supply rail and 30mA from the
-12V supply rail.
All AJHSynth modules are covered by a one year guarantee against manufacturing defects.
Note:
It is very important that the power supply ribbon cable is connected correctly, see the “adjustment and
calibration” section for an illustration of the correct orientation.
Discrete Transistor Ladder Filter
mod
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