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Doepfer A-105-4 Quad Polyphonic 24dB SSM VCF

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A-105-4 is Doepfer's 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:

  • Frequency F: manual control (common for all filters)
  • Frequency Modulation Intensity FM: manual control (common for all filters)
  • Resonance Q: manual control  (common for all filters)
  • Audio Input Level L: manual control  (common for all filters)
  • CVF control: attenuator for Frequency Control Voltage CVF  (common for all filters)
  • CVFM control: attenuator for Frequency Modulation Control Voltage VCFM  (common for all filters)
  • CVQ control: attenuator for Resonance Control Voltage CVQ  (common for all filters)
  • CVL control: attenuator for Level Control Voltage CVL  (common for all filters)
  • CVF socket: Frequency Control Voltage CVF  (common for all filters)
  • CVFM socket: Frequency Modulation Control Voltage VCFM  (common for all filters)
  • CVQ socket: Resonance Control Voltage CVQ  (common for all filters)
  • CVL socket: audio input Level Control Voltage CVL  (common for all filters)
  • FM Input 1 - 4: CV input for frequency modulation (separate for each filter)
  • Audio Input 1 - 4  (separate for each filter)
  • Audio Output 1 - 4 (separate for each filter)

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).

Application: polyphonic patches (four VCFs with same parameters) or other structures where 2 or more simultaneously controllable filters are requried (e.g. stereophonic oder quadrophonic applications)


Width: 8HP

Depth: 50mm

_hp 8