The ARP 2500: Where It All Began

ARP's first synthesizer, the 2500, had a massive impact on the electronic music industry. It was a creative behemoth unlike anything before – or since...

ARP Story Brochure 2500 (1974) by ARP InstrumentsThe Alan R. Pearlman Foundation

Imagination Into Innovation

When the ARP 2500 was released in 1970, it was seen as a remarkable and highly innovative alternative to the Moog modular systems already prevalent in universities and studios around the world. Sporting familiar sonic elements in a revolutionary format, the 2500 was capable of amazing sounds, and delivered them in a package unlike anything seen before – or since. The 2500 wasn't only ARP's first product – it was the culmination of a dream, a successful design that confirmed Alan R. Pearlman's genius and gave it to the world.

1974 Product Brochure

This 1974 brochure shows a 2500 as a single unit with its control keyboard. Additional cabinets, called wings, could be added to either side of the main cabinet, adding modules (and therefore sound creation power).

The EMEAPP 2500 Introduced

Musician and educator Don Slepian demonstrates the impressive 2500 setup at Philadelphia's Electronic Music Education and Preservation Project (EMEAPP) as well as introducing two other famous ARP instruments, the 2500's successor the 2600 and the much later Quadra.

In Celebration of 50 Years

Don Slepian uses the EMEAPP 2500 to perform a song written in honor of the synthesizer's 50th birthday in 2020.

Pete Townshend

Pete Townshend of The Who was one of the earliest and most creative users of synthesizers in rock. He used the 2500 on the famous track "Won't Get Fooled Again" from the album Who's Next, and it went on to become a staple for later albums, both solo and with his band.

The Voice Of The Cylons

The voices of the famous robots from the TV Series Battlestar Galactica were created from a complex series of audio processes... but it all began with the 2500, as explained in this video. There's a shot of the 2500 on the set of Close Encounters of the Third Kind at the end.

ARP 2500 Matrix Switches 3 (2020) by EMEAPPThe Alan R. Pearlman Foundation

A Walking Tour of a 2500

While each 2500 could be configured differently (see the version in the brochure above), a quick left-to-right tour of the unit currently restored and on display at the Electronic Music Education and Preservation Project (EMEAPP) in Philadelphia will convey a good idea of the 2500's tremendous power. We'll walk you through the modules and explain what they do...

ARP 2500 Modules 1 (2020) by EMEAPPThe Alan R. Pearlman Foundation

Starting at the far left, a reverb module allows sounds to exist in a sense of "space". Next are two types of oscillators, the basic waveforms that form the initial "body" of any sound created on the 2500 (or any other modular synthesizer). Next is a module that creates noise (useful as a sonic element or as a means of controlling other modules) and/or a slow random voltage that makes other settings on the synthesizer change unpredictably.

ARP 2500 Modules 2 (2020) by EMEAPPThe Alan R. Pearlman Foundation

The filter is the center of the 2500's tone-shaping power, allowing the frequencies of the basic oscillator waves to be contoured in many musical (and not-quite-so-musical) ways. Envelope generators create starts and endings, turning the drone of an oscillator into individual notes. The amplifier controls loudness; this one also includes a balanced modulator for metallic ringing tones. The last module in the cabinet is a power supply with fuses – and the all-important On and Off buttons!

ARP 2500 Modules 3 (2020) by EMEAPPThe Alan R. Pearlman Foundation

The second cabinet begins with a mix-sequencer module, a function unique to the 2500 at the time. It allows various sources to be mixed together or to be switched on and off one at a time, cycling through the sources. Next is another oscillator set – you can never have too many of these, or the other basic components like filters and envelopes, in a modular synth!

ARP 2500 Modules 5 (2020) by EMEAPPThe Alan R. Pearlman Foundation

After the oscillators is the Module 1045, which is essentially a tiny synthesizer within one module: an oscillator, filter, and two envelopes, with simplified controls. This packs a lot of power into a small space for when the synthesist doesn't need all the options of larger modules. The large module to the right is a sequencer, which creates cycles of up to ten steps of repeatable voltages that control up to three parameters each – usually, but not limited to, note pitches for short melodies.

ARP 2500 Modules 6 (2020) by EMEAPPThe Alan R. Pearlman Foundation

Our rule that you can never have enough of the basic building blocks of a synthesizer is amply demonstrated here, with redundant filter, amplifier, and oscillator modules. On the 2500, oscillators serve dual purposes: at high frequencies, they produce the sounds that we ultimately hear, but if you slow them down below the threshold of human hearing, they can be used as low-frequency oscillators. These create control signals that slowly vary in a cyclic way, for effects like vibrato and tremolo.

2500_13The Alan R. Pearlman Foundation

More envelopes are followed by a sample & hold: a device which takes a "snapshot" of a control voltage at regular intervals and uses it to create controls of its own, which seem unpredictable or random to the ear. Next is another filter and amplifier combined into one module, and another power supply. Our total: nine oscillators, four filters, four amplifiers, four envelopes, and a wide variety of control sources – a synth powerhouse that was easily a match for any competing system at the time.

ARP 2500 Matrix Switches 7 (2020) by EMEAPPThe Alan R. Pearlman Foundation

Matrix Patching

Uniquely, the 2500 used few or no patchcords. Instead, it had arrays of matrix switches: metal bars that could be slid on tracks to make connections between modules. These routings were easy to visualize, and allowed anything to connect to anything else. 

This was brilliant in theory, but it had issues in practice: crosstalk, or leakage of electrical signals from one bar to the next, could cause various sonic problems. Years later, the idea was revived in digital synthesizers, whose routings were crosstalk-free.

Sequences of sequences

In this solo piece for 2500, David Baron has set the Mix-Sequencer to control two other sequencers to produce a constantly shifting and changing melodic soundscape.

In the Hands of the Creator

Eliane Radigue, French electronic composer, discusses her work with the 2500. Move to the next scene to see the entire 15-minute video.

Eliane Radigue is one of France's preeminent electronic music composers. In this video, she discusses her composition and production processes, using her beloved 2500 as a canvas to illustrate her ideas. Mme. Radigue composed on the 2500 almost exclusively between 1974 and 2000.

A Giant Recognizes A Giant

Jean-Michel Jarre is the most famous electronic musician in history, world-renowned for playing live open-air concerts where a single show can attract millions of people. In this video tour of his synth collection, he pauses to honor "a part of the mythology" of synthesis.

Jean-Michel Jarre is the world's most famous electronic musician by far, even if he is practically unknown in the USA. He's sold tens of millions of records over the past 45-plus years, and his outdoor concerts have set several consecutive world records for largest crowds, up to 3.5 million people gathering for a single night. (Yes. 3.5 million.) In this informal tour of his studio and instrument collection, the 2500 (and its successor the 2600) are two of the stops along the way.

An In-Depth Tour

Musician and educator HAINBACH visited the 2500 at Willem Twee Studio in the Netherlands. Move to the next scene to access the full 22-minute tour.

If you'd like to take a deeper dive into the 2500 and what it can do, this 22-minute video by electronic musician HAINBACH provides a guided tour of the large 2500 setup at Willem Twee Studio 2 in the Netherlands.

ARP Catalog (front page) featuring the ARP Soloist Mk II, 2600 and 2500. (1973) by ARP InstrumentsThe Alan R. Pearlman Foundation

The Creation of a Legend

Although it went largely unnoticed at the time, the 2500 became one of the most famous synthesizers in history when it was featured prominently in the film Close Encounters Of The Third Kind, where it was used to communicate with an alien spaceship. That visual impact was easily matched by its many sonic achievements throughout the years.

The 2500 remained in production, largely unchanged, for the entire lifespan of ARP. Not many were sold, but those that were became useful components of many studios around the world and are still in use today. While not as famous as the 2600 or Odyssey, the 2500 was Alan R. Pearlman's first great success, and perhaps his most enduring legacy.

The 2500 remained in production, largely unchanged, for the entire lifespan of ARP. Not many were sold, but those that were became useful components of many studios around the world and are still in use today. While not as famous as the 2600 or Odyssey, the 2500 was Alan R. Pearlman's first great success, and perhaps his most enduring legacy.

And Finally...

A look at the 2500 wouldn't be complete without its famous film appearance in Close Encounters Of The Third Kind. ARP's Phil Dodds plays the keyboardist – he's seen stepping back at 3:25 to give the 2500 itself its brief moment of onscreen fame. Take a bow!

Close Encounters with Phil (1977) by unknownThe Alan R. Pearlman Foundation

Behind the scenes

Phil Dodds with the 2500

Credits: Story

Story by Mike Metlay; editorial contributions by Dina Pearlman and Mary Lock; The Alan R. Pearlman Foundation

Credits: All media
The story featured may in some cases have been created by an independent third party and may not always represent the views of the institutions, listed below, who have supplied the content.
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