OpisDoepfer A-105 is a 24dB low pass filter based on the legendary SSM2044 chip. This chip was used e.g. in these synthesizers: Korg Polysix, Korg Mono/Poly, Fairlight II, PPG Wave 2.2 und 2.3, Emu SP-1200, Siel DK600, Siel Opera 6. The first Prophets used the SSM2040 - the precedessor of the 2044 - that generates a very similar sound.
The special feature of the 4 pole low pass SSM2044 is the patented so-called "true open loop design" that delivers a characteristic fat sound not available from other devices" (extract from SSM2044 data sheet). The module will feature voltage controlled resonance and a sensitve audio input to obtain distortion - if desired.