The ARP 2500, built from 1970 to 1981, was ARP's first product. It was a monophonic analog modular synthesizer 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" mini-phone 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 proved to be a reliable and user-friendly machine, it was not commercially successful, selling approximately 100 units. A collection of the 2500s most popular modules was packaged into a single, non-modular unit as the ARP 2600, leaving out the matrix switching and more esoteric functions.

The 2500s most notable usage was in the motion picture Close Encounters of the Third Kind to communicate with aliens. The ARP technician sent to install the unit, Phil Dodds, was cast as the musician. 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.

Modules:

1974 2515 Studio Cabinet with 15 module positions SN 74-005

Modules:

1002 Power Supply

1004T Voltage Controlled Oscillator

Single precision voltage controlled oscillator offering five simultaneous waveform outputs: sine, triangle, square, sawtooth, and pulse. Provides frequency modulation, pulse width modulation and built-in waveform mixer. Also provides inverted waveform outputs.

1005 Modamp

A complex function module containing a precision balanced modulator, a voltage controlled amplifier, and switching circuitry.

1006 Filtamp

A combination of a voltage controlled low pass filter, a voltage controlled amplifier, and a mixer.

1016 Dual Noise / Random Voltage Generator

Contains two independent noise sources and filters to derive pink noise and continuous slow random voltages. Slightly weak signals from both noise generators. Very weak signal from slow random noise generator A.

1023 Dual Voltage Controlled Oscillator

oscillators offering five simultaneous waveform outputs: sine, triangle, square, sawtooth, and pulse. Provides frequency modulation, pulse width modulation, and built-in waveform mixer. No signal from left oscillator.

1027 Ten Position Sequencer

Flexible sequential voltage generator. Capable of creating complex switching patterns with 30 preset voltages.

1033 Dual Delayed Exponential Envelope Generator

A flexible envelope generator that includes a variable trigger delay.

1036 Dual Sample & Hold / Random Voltage Generator

Contains two low-drift sample and hold circuits, two noise sources, and two voltage controlled pulse generators.

1045 Voltage Controlled Voice

Combination of two Envelope Generators / Voltage Controlled Oscillator / Voltage Controller Filter / Voltage Controlled Amplifier. Used as preset voice.

1047 Multimode Filter / Resonator

Combination high-pass, low-pass, band-pass and band-reject filter. Ultra-high Q. Voltage controlled center frequency and resonance.

1050 Mix/Sequencer

A combination of a sequencer, mixer, and analog gate. Serves dozens of functions as a utility mixer, sequencer and preset function selector. This module is linked to the1027 sequencer module.