The A-124 filter design is based on the 1970’s EDP Wasp synth. Most things about the Wasp were different, from the flat touch yellow and black keyboard to the unusual filter design. The filter design is a 12dB/oct multimode type, based around digital inverters, abusing their designed purpose and using them as operational amplifiers which leads to distortion, and generally causing a dirty sound characteristic of this filter design.
The filter has a band pass output and a combined low/notch/high pass output, this output has a balance control between low pass and high pass providing a notch filter when central.
Due to the design of this filter, it will not self oscillate, and certainly offers a different kind of filter sound, to any of the other VCF modules in the A-100 range.