The A-105-4 is a polyphonic filter that contains four identical 24dB Lowpass filters (SSM2044 type). The component has been used in many classic synthesizer among which the Korg Polysix, Mono/Poly, Fairlight II, PPG Wave, Emu SP-1200. It has available common manual controls and CV inputs with attenuators for these parameters.

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 . 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.