Doepfer A-105-4 Quad Poly VCF

The A-105-4 is a quad filter for polyphonic patches. It is based on the SSM2044 / SSI2144 chip, meaning the same component used in Korg Polysix, Mono/Poly, Fairlight II, PPG Wave, Emu SP-1200 and many other classic synthesizers. The filter has a very rich sound character. Its resonance begins coloring the sound rather early. High settings lead the module into self-oscillation. Then, the A-105-4 emits clean sine waves. Thanks to a gain stage at the input, signals can be distorted before reaching the filter. On top of that, there are lots of CV inputs for modulation purposes.

The A-105-4 is a quadruple low-pass filter based on the SSM2044 / SSI2144. It features an edge steepness of -24 dB per octave. Each filter channel is equipped with its own audio input and output as well as a FM input. Thus, the A-105-4 can be easily used as part of polyphonic patches. Simply connect VCOs and envelopes with audio and FM inputs. Then, add a quad VCA (plus additional envelopes) after the filter module and voila, the polyphonic patch is ready to go. Input level, cutoff frequency, resonance and FM intensity are controlled by just one set of potentiometers to guarantee consistent results in all four voices. Additionally, there is a CV input with attenuator for each of the four parameters. High level settings result in distorted sound.

Connectors:

Four audio inputs
Four FM inputs
Four audio outputs
Cutoff CV input
Resonance CV input
Master FM CV input
Level CV input

3 U Eurorack module, 8 HP wide, 50 mm in depth