# ARP 2500

The ARP 2500 is a monophonic (or duophonic) analog modular synthesizer. It was the first product of ARP Instruments, Inc., built from 1970 to 1981. Although only about 100 units were made, Sound on Sound called it "undoubtedly one of the most important electronic musical instruments ever made." It is notable for offering a huge range of programming possibilities via matrix switches instead of conventional patch cables. However, it was also very large, difficult to program, and expensive. Demand from musicians for a synth that was more affordable lead ARP to develop the 2600 and the Odyssey in the years after the 2500's release.

## Features

Initially made by Alan Pearlman’s company Tonus Inc with the name Series 2000 system, the company changed its name to ARP (the founder’s initials) and renamed it the 2500.
Designed by Alan Pearlman, Dennis Colin and David Friend, the 2500 was advertised as having two major advantages over other synths: stable oscillators with “no audible drift” and matrix switches instead of patch cords which visually obscure modules. The oscillators combined Alan Pearlman’s patented exponential converters with a dual core design, resulting in good tuning stability compared to competitors.
The sliding matrix switches found above and below the modules and are the main method of connection between modules and from the keyboards to the modules. There are rows of 1/8" miniphone jacks at the end of each row of matrix switches, to interconnect rows of switches, wing cabinets or as inputs and outputs. Keyboard connections are "normalled" (connected by default) to the top left mini-jacks. Other major new features introduced in the 2500 were duophonic keyboards and state-variable filter/resonators. The main 2500 cabinet can hold 15 modules, and optional wing cabinets can each hold 8. The matrix switch interconnection scheme allow any module's output to connect to any other module's input. Unlike the patch cords found on the modular synths of competitors like Moog and Buchla, which can obscure control knobs and associated markings, the matrix implementation enables a cable-free experience. However, the matrix switches developed a reputation for dirty connections and cross-talk.
The earliest 2000 series cabinets could hold 8, 15, or 19 modules. The later cabinets were taller, and available in 8 or 15 modules sizes. There was also a portable 8 module version, which they marketed as an expansion of the later 2600.
A range of five-octave keyboard options were available, including monophonic, split, duophonic, and dual versions. Split keyboards have one or two left octaves with reverse coloured keys, and either section could be monophonic or duophonic, offering control of up to four voices on a single keyboard.
Although the 2500 proved to be a reliable and user-friendly machine, it was not commercially successful. Systems cost up to $12,000 (almost half the average US house price at that time) and the 2500 was introduced at a time when sales of large modular synthesizers were starting to fall, so they only sold approximately 100 units. ARP initially produced 14 module types with many more planned to follow, but only a few new modules made it into production, while others reached the prototype stage.

### Modules

* 1001 Blank module
* 1002 Power control
* 1003 Dual envelope generator
* 1003a Dual envelope generator
* 1004 VCO
* 1004p VCO with mix pots
* 1004r VCO with mix rocker switches
* 1004t VCO with mix toggle switches
* 1005 Modamp (Modulator/VCA)
* 1006 Filtamp (Moog filter plus VCA)
* 1016 Dual noise / random voltage source
* 1023 Dual VCO
* 1026 Preset voltages
* 1027 10 stage Sequencer
* 1033 Dual delayed envelope generator
* 1036 Dual Sample & Hold
* 1045 Voltage controlled voice (1004, 1006 & 1003 in one module)
* 1046 Quad envelope generator (1003a & 1033 in one module)
* 1047 Multimode filter / resonator
* 1050 Mix/Sequencer
Three additional modules existed only as prototypes or mock-ups: the 1012 Convenience module, the 1035 Triple modulator, and the 1040 Noiselator.
A collection of the 2500's most popular modules was redesigned into a single, semi-modular unit as the ARP 2600, leaving out the matrix switching and adding some new functions.

## Notable users and appearances

John Kongos first used one at Trident Studios in 1971, then in 1973 he acquired his own - it was used extensively at his Tapestry Studio, on his own recordings as well as Def Leppard (Pyromania), Mutt Lange, Alain Chamfort, Tony Visconti, Ryan Ulyate and many others.
In 1972 Pete Townshend of the Who used an ARP 2500 on the Who's Quadrophenia. Townshend built his own home studio to experiment and record, due to the enormous amount of time he spent creating his groundbreaking synthesizer orchestrations on both Quadrophenia, and the movie version of Tommy.
The ARP 2500 was extensively used by British producer David Hentschel on recordings such as "Funeral for a Friend" from Elton John's 1973 album Goodbye Yellow Brick Road. Jeff Wayne's 1978 multi-platinum selling album War of the Worlds features the ARP 2500, including the sound of Martian speech.
Paul Bley used a 2500 on his Synthesizer Show album and in his live shows.
In the 1977 motion picture Close Encounters of the Third Kind, a 2500 unit is used to communicate with aliens. Phil Dodds, ARP's Vice President of Engineering, was on set to install and manage the synthesizer; Steven Spielberg, liking his looks, cast him on the spot as an extra to play the 2500. The unit featured in the film consisted of a fully loaded main unit, two fully loaded wing cabinets and dual keyboards in a custom case. It was damaged by the artificial smoke/fog used on the film set.
It has been used by artists such as Aphex Twin, David Bowie, Vince Clarke, Ekseption, Faust, John Frusciante, Jean Michel Jarre, Cevin Key, Kraftwerk, Jimmy Page, Vangelis and the Who. The composer Éliane Radigue has worked almost exclusively with the 2500.
While ARP no longer exist, a number of companies make modules based on the 2500. CMS make modules to fit 2500 cabinets if you are lucky enough to own one and Mos-Lab make a clone, although they use mini jacks in place of the Cherry matrix switches, which are no longer available. CMS, Behringer and AMSynths make Eurorack modules based on ARP2500 modules.