A voltage controlled filter design introduced by ARP Instruments in the early 1970s, after Moog Music threatened a patent lawsuit over ARP's earlier, transistor ladder-based design. The 4075 is a unique design that is based on a transistor ladder, but it uses a type of op-amp known as a Norton amplifier to drive the integrating capacitors, and provide buffering and isolation between filter stages. One benefit of this design is that it eliminates control voltage feedthrough. The 4075 was used in later production Odyssey, 2600, and Axxe models.
Nearly every example of the 4075 filter built by ARP contains a design error which sharply limits the maximum value of the cutoff frequency, creating the often-repeated perception that the filter sounds "dull". An easy modification, replacing four resistors in the circuit, will allow the cutoff to reach much higher frequencies and improve the bandwidth response of the filter.