Doepfer A-105

24dB low pass filter

The A-105 is a 24dB low pass filter that bases on the SSM 2044 chip that was used amongst others in following units: 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 filter convinces with a very powerful sound. The resonance starts quite early to color the signal and makes a big range of sounds possible up to self-oscillation. The latter provides a very clean sine wave – no wonder, because the SEM2044 chip wasn´t designed only as a filter core but also as a sine wave oscillator.

The A-105 bases on the patented so-called “true open loop design” which generates a very fat sound. The filter works with a slope of -24dB per octave and provides voltage controllable resonance up to self-oscillation. The audio input is sensitive so you can distort the audio signal at the input if desired. there´s a volume control at the audio input, potentiometers for setting the cutoff frequency and resonance as well as attenuators at the CV inputs for cutoff and resonance.

Specifications

Width: 8HP
Depth: 45 mm (measured from the rear side of the front panel)
Current: +30mA (+12V) / -20mA (-12V)