AI Synthesis AI004 OTA VCF 2019 Silver - Modular Eurorack MS-20 Filter

The AI Synthesis OTA Voltage Controlled Filter is a Eurorack-formatted take on the VCF found in the classic Korg MS-20 synthesizer, adapted/designed by Sagittronics. The MS-20 used two identical VCFs with one in highpass mode chained into one in lowpass mode (a “series” configuration); this module can function as either half (via the HP/LP switch), or two of them can be used together to get the full MS-20 experience.

While many Eurorack MS-20 filters use op-amp stage buffers, this VCF uses the same Darlington buffers used by the original late-model MS-20s for a more authentic sound. Also like the original, the resonance path features a diode-clipping section similar to the one found on the Ibanez Tubescreamer (or any number of other guitar overdrive pedals). Using the In (input attenuation) and Res (resonance) controls, the signal can be overdriven as it passes through. We’ve particularly enjoyed doing this in the highpass mode with a V/Oct or Sample-&-Hold signal run into CV2.

Speaking of—the AI004 features a pair of frequency CV inputs, CV1 & CV2. The CV1 input is run through an attenuverter, allowing for both attenuation and/or inversion of the CV signal. This is key for using the highpass mode as a negative-going voltage is needed to "open" the filter (the reverse of lowpass where positive-going voltages open the filter). CV2 is an additional un-attenuated input. More info on how these work can be found in the manual.

Specs:

•  Size: Eurorack/8HP
•  Depth: 60mm
•  Lowpass Slope: 12 dB/octave
•  Highpass Slope: 6 dB/octave
•  Decay: 10ms min. 20s max.
•  Release: 100ms min. 7s max.
•  Current Draw: 15mA@-12V, 15mA@+12V

This module was built, assembled, tested, and packaged by AI Synthesis in Portland, OR. Please refer to the Ai Synthesis website for additional detail.