The ARP 2600 is a semi-modular analog subtractive audio synthesizer produced by ARP Instruments, Inc. History Developed by a design team headed by ARP namesake Allen R. Pearlman and engineer Dennis Colin, the ARP 2600 was introduced in 1971 as the successor to ARP's first instrument, the ARP 2500, at a retail price of US$2600. Unlike other modular systems of the time, which required modules to be purchased individually and wired by the user, the 2600 was semi-modular with a fixed selection of basic synthesizer components internally pre-wired, with clear text labels and front panel screen printed graphics indicating the function of different sections of controls, and the signal flow between them. The 2600 was thus ideal for musicians new to synthesis, due to its ability to be operated either with or without patch cords. On its initial release it was heavily marketed to high schools and universities. Features and architecture The ARP 2600 features three VCOs, a 4-pole (24 dB/octave) Low-pass filter, a VCA, a ring modulator, sample and hold, a white/pink noise generator, microphone preamp, spring reverb, two envelope generators, and a four-octave keyboard. In 1973, Tom Oberheim, who was an ARP dealer, produced a kit that converted the keyboard into a duo-phonic keyboard capable of triggering two different oscillators simultaneously. The following year, ARP adopted this improvement and introduced the Model 3620 duo-phonic keyboard, which also included delayed vibrato as well as single and multiple triggering functionality. All versions of the ARP 2600 produced through 1976 utilized ARP’s Model 4012 filter, which was an imitation of Robert Moog's 4-pole "ladder" VCF, which became the subject of a patent dispute eventually settled out of court, and was replaced by an ARP filter design, the Model 4072. Models Model 2600 “Blue Meanie” (early 1971): The earliest 2600s were assembled in a small facility on Kenneth Street in Newton Highlands, Massachusetts, during ARP's infancy as a company. Housed in a bright blue and light gray aluminum case with a keyboard mated to the synthesizer, this version was nicknamed the "Blue Marvin" (after Marvin Cohen, ARP’s CFO at the time) but is now commonly referred to as the "Blue Meanie.” Model 2600C “Gray Meanie” (mid-1971): The 2600C was produced in the ARP factory, and featured a gray control panel and updated keyboard model 3604C. Only 35 “Gray Meanies” were produced. Model 2600P (late-1971): The 2600P was housed in a suitcase-style vinyl-covered