ARP Quartet (1979–1981)

An American badge on an Italian ensemble machine - four preset voices, a real VCF, and a reputation that outlived the company that sold it.

Overview

Don't expect the bite of a 2600 from the ARP Quartet. Expect a string machine with a little more going on under the hood, and it delivers. It's a preset-based ensemble synth built on analog divide-down tone generation, with a 49-key keyboard that plays fully polyphonically. No voice-stealing, no note-count ceiling. Four sections make up the instrument: Brass, Strings, Organ, and Piano. Any two can be layered at once, and that's where the Quartet starts to act more like an arrangement tool than a one-trick pad machine.

Most collectors learn the story behind the badge first. The Quartet is a rebadged Siel Orchestra, an Italian ensemble synth built in Pescara and sold under ARP's name with a new faceplate and a handful of internal tweaks. ARP Instruments, Inc. was scrambling by 1979, and rebadging an existing Italian design was cheaper than engineering a new flagship. People usually tell that as an embarrassment. The Quartet sounds Italian because it is Italian, and Siel's strength was reliable, musical-sounding ensembles rather than bleeding-edge design.

The preset concept isn't what keeps the Quartet interesting. Plenty of machines did presets. The shaping you get inside that concept is the draw. A two-pole voltage-controlled low-pass filter with its own ADSR envelope is unusual on a preset synth, and it turns a static ensemble box into something you can play dynamically. The triple bucket-brigade delay lines that give the instrument its shimmer are borrowed straight from the Solina String Ensemble, and the same circuitry also drives the vibrato and tremolo. The Quartet doesn't try to be a lead synth or a bass machine. It's a mood generator.

Key Features

Four Sections, Two at a Time

Brass, Strings, Organ, and Piano cover the front panel, and any two can be layered simultaneously. Each section has its own sub-voicings: Brass splits into trumpet and trombone, Strings into cello and violin, Organ pairs with Celeste under the Reed label, and Piano pairs with Honky Tonk. Layering Brass over Strings, or Organ under Piano, gives combinations the individual voices can't reach alone. Each section also has its own tuning and vibrato depth, so stacked voices keep some separation instead of collapsing into a single smear.

Two-Pole VCF with Shared ADSR

Most preset ensemble synths of the late '70s give you a tone switch and a volume slider. The Quartet gives you a two-pole voltage-controlled low-pass filter and a dedicated ADSR envelope, which is an unusual amount of control for the category. The envelope is shared across sections rather than per-voice, but it still lets you shape the filter's response in real time.

Variable Attack and Release

The Brass and Piano sections offer variable attack, so a trumpet stab can be snapped tight or eased in softly. The Strings section gets its own release control, which is rarer than it should be on machines of this class. Most string synths cut off the moment you lift your fingers. Here you can stretch the tail of a string chord, which makes phrasing possible.

Triple BBD Ensemble and Modulation

The Quartet's shimmer comes from triple analog bucket-brigade delay lines, the same approach used in the Solina String Ensemble and the ARP Omni series. The effect is baked in rather than switchable. It produces the slow pitch and timing drift that makes an ensemble sound like an ensemble instead of a stack of oscillators. An LFO handles vibrato and tremolo, and it's fed by the same BBD circuitry.

ARP Revisions to the Siel Design

ARP didn't simply slap a logo on the Orchestra. Internal resistor values were tweaked - a 390K resistor became 680K in the ARP version - and the cosmetics were updated with ARP's signature blue-and-silver faceplate. The changes are minor, but they mark the boundary between the two instruments if you're trying to identify what's inside a given unit.

Historical Context

By 1979, the company that had challenged Moog with the 2600 and the Odyssey was running on fumes. Management infighting, financial missteps, and a failure to keep pace with digital advances had left ARP scrambling. Rather than develop a new flagship, the company took a cost-saving shortcut: rebadge the Siel Orchestra and sell it as its own. The market was shifting fast. Polyphonic synths like the Yamaha CS-80 and Sequential Prophet-5 offered full programmability, while string machines like the Solina and Logan String Melody owned the budget end. The Quartet sat awkwardly between the two camps.

Critics at the time dismissed it as a cash grab, and the judgment stuck. Sound on Sound later called it "nasty," and even sympathetic observers treated it as a stopgap. At its 1979 NAMM debut in Atlanta, Sound-Arts (October 1979, p.40) noted that the Quartet was designed to give players brass, strings, organ, and piano at minimum cost and with minimum operating difficulty. ARP folded in 1981, just as the Quartet was being phased out. The instrument outlived the company that sold it, and the reassessment has been slow but real.

Collectibility & Value

Working Quartets typically trade between $1,200 and $1,800, with professionally restored examples reaching $2,200. Non-working units move for $600 - $900, usually to technicians who know the repair path. An undated eBay listing for a working example was asking $1,775, which sits squarely in the middle of the working range.

The biggest threat to longevity is capacitor failure. The power supply and audio path rely on electrolytics that dry out over time, and when they go, the symptoms range from hum to channel dropouts to complete power failure. A full recap is strongly recommended for any unit that hasn't had one, and runs $300 - $500 depending on the technician. Some owners also report BBD chips degrading over the years, which shows up as lost chorus depth or a thinning of the ensemble effect. These aren't user-replaceable and require careful sourcing.

Keyboard contacts are the other recurring headache. The Quartet uses a resistive strip design that wears out, causing notes to stick or fail to trigger. Cleaning helps temporarily, but worn strips usually need replacement. Cosmetically, the rear panel is prone to rust in humid climates, and the side-panel paint chips easily thanks to ARP's cost-cutting on primers. None of that is functionally fatal, but it's a negotiating lever.

Buying advice is straightforward. Test every section individually and in combination, listen for evenness across the keyboard, check that the envelope responds consistently, and confirm the chorus is present and stable. Let the unit warm up for fifteen minutes before deciding, since some develop hum or drop voices as they heat.