AI Synthesis - AI004 OTA VCF Used
AI Synthesis

AI Synthesis - AI004 OTA VCF Used

Regular price $100.00

 AI Synthesis - AI004 OTA VCF Used

AI004 OTA Voltage Controlled Filter

This OTA Voltage Controlled Filter uses the same filter structure as the venerable Korg MS 20 Filter. The filter is switchable between Lowpass and Hi Pass modes, and features an updated diode gain stage in the resonance section. This circuit was adapted by Sagittronics, who does excellent work.

The VCF will overdrive and distort in both the HP and LP modes, and the resonance can self-oscillation. As with the MS 20 Filter, the Low Pass slope is 12dB/octave and the High Pass slope is 6dB/octave. The CV input is an attenuverter, allowing for dynamic control-voltage of the cutoff.

As with most OTA filters, (as well as diode ladder, cascade, CEM, and SSM designs,) resonance is achieved via negative feedback, the non-resonanced signal will slightly drop. When used in conjunction with a VCA, this is trivial.
There are ways to compensate for this by injecting some of the original signal into the feedback loop, or adding extra gain circuitry, but this has its own issues, and was avoided in this design, in part for authenticity. In the “normal” mode, there is a normal volume drop, and in the “extended resonance mode” you will see a greater volume drop to the “passed signal.”


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