The ARP 2500 is a monophonic analog modular synthesiser created by Alan Robert Pearlman in 1970-1981, who was a American manufacturer of electronic musical instruments. It was equipped with a set of sliding matrix switches above each module. These were the primary method of interconnecting modules. There were also rows of 1/8″ miniphone jacks at the end of each row of matrix switches, to interconnect rows of switches. The main 2500 cabinet could hold 12 modules, and optional wing cabinets could each hold 6. The matrix switch interconnection scheme allowed any module’s output to connect to any other module’s input, unlike the patch cords of competitive units from Moog and Buchla which could obscure control knobs and associated markings, but it had the disadvantage of greater cross-talk.
Although the 2500 was a reliable and user-friendly machine, it was not very commercially successful. The 2500 most popular modules was packaged into a single, non-modular unit, the ARP 2600, which left out the matrix switching and more esoteric functions.