ARP Omni-1 (1975–1977)

The first chord is warm, shimmering and very wide. It is a string machine, and it sounds like one.

Overview

The ARP Omni-1 is a polyphonic string ensemble and a monophonic synthesizer in one box. It has been around nearly fifty years and still works. Plug it in and give it the usual five-minute warm-up. Then the chorus-phased strings come up. The cause is ARP's proprietary 3-voice Chorus Phaser circuit, which modulates the string tones in three slightly different directions and makes a very wide stereo image. This is the sound of late '70s atmosphere - the sigh behind The Cars' "Moving in Stereo," the haze of Joy Division's later recordings, and plenty of film cues that needed to sound both synthetic and human.

It is not just a preset string box. It is a hybrid, split into three sections: the polyphonic Strings section (Violin and Viola waveforms), a monophonic Synthesizer section with a voltage-controlled filter and ADSR envelope, and a Bass section that, unlike its successor, runs through the same VCF. That gives it a fat low end for a machine of its era. The keyboard is divided so you can play strings with your right hand and trigger the synth or bass lines with your left, all at once. The Strings and Synthesizer sections each have their own outputs, so you can send them to separate amps or effects chains. Pan the strings wide and keep the synth lead tight and dry. It was a clever workaround for true polyphony, and for 1975 it felt like magic.

The Omni-1 is paraphonic, not fully polyphonic. All notes share a single filter and envelope, so a chord rises and falls together. That is a limitation, but it also gives the sound a cohesion, like an orchestra responding as one. The synth section is modest and built on ARP's trusted analog circuitry: a single oscillator with sawtooth and square waveforms, a 4-pole low-pass filter, and an LFO that feeds vibrato and filter modulation. It won't scream like a 2600 or growl like an Odyssey. It is warm and rounded, and it gets expressive when paired with the decay-time foot controller that adjusts envelope release on the fly.

This was not ARP's first string machine - the Quartet and Solina had already laid the groundwork. But the Omni-1 was the first to bring synthesis into the formula without hurting the string engine. It was aimed at one job: a portable, reliable orchestral backdrop with enough flexibility to let players shape their own voice. Between 1975 and 1977 it did that very well.

Specifications

Key Features

The Chorus Phaser That Changed Everything

The patented 3-voice Chorus Phaser became the sonic fingerprint of a whole generation of string machines. Simple chorus effects duplicate and modulate the signal. ARP's design splits the string output into three parallel paths, each modulated at slightly different rates and depths, then recombined in stereo. That mimics the natural tuning variations of real string sections, so the Omni-1 never sounds static, even holding one chord for minutes. The effect is applied only to the string section, leaving the synth and bass dry and direct. That lets players layer textures without muddying the mix. Later string machines copied the concept, but few matched ARP's original.

Synth Section With Real Teeth

Many string machines treated the synth portion as an afterthought. The Omni-1's monophonic section is built with serious analog intent. The 4-pole VCF is the same topology found in ARP's flagship synths, and it handles everything from warm pads to snarling leads when driven hard. A full ADSR envelope (unlike the simpler AR on the strings) lets you shape notes with precision, and the LFO modulates both pitch and filter cutoff. It won't replace a modular rig, but it is a legitimate lead and bass voice that holds its own in a mix. The bass section routes through this same filter, giving the Omni-1 a low-end weight that the Omni-2 would lose in its redesign. That single change makes the Mk I the preferred version for players who want both atmosphere and punch.

Split Personality, Seamless Integration

The Omni-1 is three instruments designed to work together. The keyboard splits at a user-selectable point, with strings above and synth or bass below. A mix control slider blends the string and synth outputs internally, so you can get hybrid tones between orchestral and electronic. A cello line with a hint of sawtooth grit is one dial away. So is a bass that starts with a string attack before dropping into filtered depth, with no patch cables. The interface is simple, intuitive and powerful.

Historical Context

The Omni-1 arrived when keyboardists were desperate for polyphony. In 1975, true polyphonic synths were either nonexistent or prohibitively expensive - Moog's Polymoog wouldn't arrive until 1975 and cost nearly twice as much. Most players relied on Mellotrons for orchestral textures, but those machines were heavy, fragile, and needed constant tape maintenance. The Omni-1 offered a portable, solid-state alternative that made lush, moving string sounds with the reliability of analog electronics. It wasn't meant to replace the Mellotron. It was meant to replace the entire string section.

ARP positioned the Omni-1 as a "symphonic electronic keyboard." It competed directly with the Eminent Solina (whose string engine it improved upon), the Roland RS-202, and the Korg PE-1000, and it stood apart with its integrated synth section and superior build quality. Where others offered presets and little else, the Omni-1 gave players control over filter sweeps, envelope shapes, and signal routing. It wasn't a workstation, but it gave composers and gigging musicians flexibility without complexity.

The timing was good. It was released just as prog rock was peaking and new wave was beginning to stir, and the Omni-1 found its way into studios and touring rigs quickly. Tangerine Dream used it for atmospheric beds, Kraftwerk for rhythmic precision, and The Cars for the creeping tension in "Moving in Stereo." The Omni-2 arrived in 1978 - lighter and cheaper, but with a simplified synth section and no bass VCF. The original Mk I was ARP's best-selling instrument, with around 4,000 units built, a remarkable number for a $2,250 synth in the mid-'70s.

Collectibility & Value

Today the ARP Omni-1 trades in a narrow but passionate market. Well-maintained units sell between $2,800 and $4,200. Pristine examples in original road cases fetch premiums, especially with the original manual and spec sheet. The Calzone flight case is heavy but sought after, and a sign the synth was taken seriously by its original owner. Cosmetic condition matters less than function. The wooden side panels can be refinished, but a dead Chorus Phaser or unstable tuning can cost $800+ to repair.

The biggest threat to longevity is capacitor failure. The power supply and audio path rely on aging electrolytics that dry out over time, leading to hum, channel dropouts, or complete failure. Any unit that hasn't been serviced in the last 15 years needs a full recap. Service technicians observe that the membrane switches, while durable, can develop contact issues, and the slider potentiometers often need cleaning or replacement. The key bushings wear out, leading to wobbly keys, but replacements are available from specialty synth shops.

Buyers should test every function: the split point, the mix control, both outputs, and the foot controller. The Chorus Phaser should sound smooth and shimmering, without crackling or imbalance. Tuning stability across the keyboard is a key indicator of health - drift of more than a few cents suggests the need for calibration or oscillator board work. Units advertised as "fully serviced" from reputable shops like Synthchaser or Ripped Ear are worth the premium. Untested "as-is" listings on eBay are lottery tickets.

Modern software emulations like GForce's Virtual String Machine and Puremagnetik's Kardoni copy the sound, but they can't replicate the physicality of a real machine - the weight of the keys, the glow of the LEDs, the way the sound fills a room. The Omni-1 is a working instrument, and it still delivers a sound no plugin has fully duplicated.

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