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The Doepfer A-105-4 is their first polyphonic filter and contains four identical 24dB Lowpass filters (SSM2044/SSI2144 type). It has available common manual controls and CV inputs with attenuators for all parameters.
The module has these controls and in/outputs are available:
Each filter has available a separate FM input as well as an Audio Input and Audio Output. The FM inputs are typically connected to the outputs of the associated envelope generator (e.g. A-141-4). The envelope amount for all four filters is controlled by the FM knob and the CVFM input by means of four built-in VCAs, which are controlled by the FM control and CVFM input. This allows also voltage control of the envelope amounts.
In addition common frequency modulation for all filters is possible (e.g. by an LFO). For this the CVF input with attenuator can be used.
The range of the audio input level control (L) allows also clipping/distortion with typical A-100 audio levels (e.g. from A-111-4) at the filter inputs. Even this parameter is voltage controllable as well as the resonance (Q).