Quad Poly VCF

A-105-4 is Doepfer's first polyphonic filter and contains four identical 24dB Lowpass filters (SSM2044 type). It has available common manual controls and CV inputs with attenuators for these parameters.

The module has these controls and in/outputs are available:

• Frequency F (manual control)
• Frequency Modulation Intensity FM (manual control)
• Resonance Q (manual control)
• Audio Input Level L (manual control)
• CVF control (attenuator for Frequency Control Voltage CVF)
• CVFM control (attenuator for Frequency Modulation Control Voltage VCFM)
• CVQ control (attenuator for Resonance Control Voltage CVQ)
• CVL control (attenuator for Level Control Voltage CVL)
• CVF socket (Frequency Control Voltage CVF)
• CVFM socket (Frequency Modulation Control Voltage VCFM)
• CVQ socket (Resonance Control Voltage CVQ)
• CVL socket (Level Control Voltage CVL)
• FM Input 1 - 4
• Audio Input 1 - 4
• Audio Output 1 - 4

Each filter has available a separate FM input as well as an Audio Input and Output. The FM input is typically connected to the output 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).