Doepfer - A-109
Module A-109 is a voltage controlled audio signal processor containing the following components:
VCF: 24 dB Low Pass with voltage controlled resonance
PAN: Panning unit (two complementary controlled VCAs)
The VCF is a standard 4 pole low pass filter with voltage controlled resonance. The filter has a so-called "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 main VCA has a combined exponential/linear control scale: exponential from about 0...+200mV (corresponding to about -100dB ... -20dB), linear from about 200mV...+5V (corresponding to -20dB...0dB). 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 as well as 2 CV inputs (one with attenuator).
The gains of the panning VCAs are complementary, beeing equal and half of maximum at about +2.5V CV. 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 privided that no jack plug is inserted to the VCA audio input socket.
The A-109 module is based on Doug Curtis' CEM3379 that was used in many Sequential™, Ensoniq™ and PPG™ synthesizers.
For more detailed information please look at the English user's manual A109_man.pdf