The A-109 is a combined VCF, VCA & Voltage Controlled Pan.
The VCF is a 4 pole low pass type with voltage controlled resonance. The filter has a "constant amplitude versus resonance design", i.e. the peak-to-peak output level remains within 6dB when the output waveform rings from added resonance. Manual controls for frequency and resonance are available as well as 2 CV inputs for both (one with attenuator). The frequency range is about 5 Hz ... 20kHz, resonance ranges from 0dB up to self oscillation.
The VCA has a combined exponential/linear control scale: exponential from about 0...+200mV, linear from about 200mV...+5V. The "rounded" knee at the scale bottom allows an envelope to decay to zero with a natural exponential sound. Manual control for amplitude is available, with 2 CV inputs (one with attenuator).
The gains of the panning VCAs are complementary. The control scales are linear between about +1 and +3.5V CV, becoming logarithmic beyond these extremes. Manual control for panning is available as well as 2 CV inputs (one with attenuator).
The audio in/outputs of the module are normalized, e.g. the VCF output is fed into the VCA input and VCA out to panning in.
