ARP String Synthesizer (1975)

A pad swells under a lead line. Two instruments share one wooden chassis.

Overview

This is one of the hardest-to-find synths of the analog era. Documentation shows it was a hybrid. It combined the polyphonic sound of the Solina String Ensemble with the monophonic lead of the ARP Explorer. The Solina side gave violins, trumpets and cellos. The added Explorer circuitry let a player cut through that ensemble with a sharp, tunable VCO lead. Owners report that this setup let a player back a full band with strings and solo over the top without any external gear.

Manufacturing records indicate the unit was built in Bodegraven, Netherlands by Eminent B.V., then re-branded for the American market under the ARP logo. That put Dutch organ technology together with American synth design, and the result offered full polyphony alongside traditional voltage control. The chorus effect comes from the Solina section. It adds a phase-shifting animation that makes the strings sound thicker and more alive, and that sound defines the disco and progressive rock of the late seventies.

Surviving units are very rare. Supposedly only about 100 were ever produced, which makes this hybrid far scarcer than the standard Solina String Ensemble found in many studios. Collectors note that the rarity comes from fitting two distinct synthesis engines behind a single control panel. When it works, strings and monophonic leads coexist without patching. That was convenient, and it was also costly to manufacture.

Specifications

Manufacturer	ARP Instruments Inc. (Built by Eminent B.V., Netherlands)
Production Years	1975 (Hybrid Model)
Original Price	Not documented in available research
Keyboard	49 Keys
Polyphony	Full Polyphonic (Strings) / Monophonic (Lead)
String Voices	Violin, Viola, Cello, Contra-Bass, Horn, Trumpet
Lead Oscillator	VCO (from ARP Explorer architecture)
Effects	Built-in Chorus/Ensemble Effect
Controls	Crescendo (Attack), Sustain Length (Decay), Volume Sliders
Outputs	Gate and Trigger Outputs (Polyphonic Keyboard)
Chorus Switch	On/Off (SE-II Architecture)
Technology	Divide-Down Oscillators (Strings) + VCO (Lead)
Case Material	Wood or Wood-like Panels
Production Count	Approximately 100 Units
Power Supply	Internal (Voltage Rails for Analog Circuits)
Tuning	Global Tuning Knob
Architecture	Hybrid (Solina String Ensemble + ARP Explorer)

Key Features

Hybrid Synthesis Architecture

The defining feature is divide-down string technology paired with voltage-controlled lead synthesis. The Solina section uses top-octave divide-down oscillators, common in electronic organs of the era, to get full polyphony across the keyboard. Every key pressed triggers a string voice, with no need for multiple discrete oscillators. Layered beneath this is the ARP Explorer monophonic synthesizer circuit, which brings in a true VCO for lead lines. Service technicians observe that a player can hold a string chord while playing a bass line or lead melody at the same time, which standalone string machines couldn't do.

Animated Chorus Effect

The built-in chorus is a core part of the string voice. Research indicates the effect is achieved by passing the sound through three modulated delay lines that cause a phase-shifting effect. That makes the strings lush and shimmery and hides the static nature of the divide-down oscillators. On their own, the individual string voices are quite unrealistic and not particularly usable. Combined as an ensemble with the chorus engaged, the texture becomes thick and animated. Owners report that the chorus circuit is the heart of the instrument's appeal, because it supplies the motion needed to mimic a real orchestral section.

Performance Control Layout

The control panel is a discrete layout built for quick adjustments during a performance. Sliders for Crescendo (attack) and Sustain Length (decay) shape the envelope of the string section, with no menus. The global tuning knob keeps the divide-down oscillators aligned with the monophonic VCO. Documentation shows the keyboard provides Gate and Trigger outputs from the polyphonic section, so external sequencers or drum units can sync with the string performance. With control voltage outputs sitting next to preset string voices, the instrument landed between a preset organ and a modular synthesizer.

Historical Context

ARP Instruments dominated the American synthesizer market throughout the 1970s, competing directly with Moog Music. ARP focused on voltage-controlled modular and semi-modular systems like the 2500 and 2600. Touring musicians, though, wanted polyphonic instruments with reliable tuning and full chords. The Solina was created by the Dutch company Eminent in 1974, derived from the string section of Eminent's 310U Organ. ARP bought the rights to re-brand the Solina for the US market and used its distribution network to place these string machines in studios across North America.

This hybrid was an attempt to bridge the string ensemble market and the lead synth market. Competitors like the Polymoog and ARP Omni were emerging. They offered polyphony but often lacked the specific orchestral texture of the Solina. By adding the Explorer lead engine, ARP aimed to give keyboardists a single solution, since they previously had to stack a string machine on top of a monophonic synth. The industry favored instruments that saved rack space while staying versatile, though the complexity of this hybrid limited its production volume compared to the standard Solina Ensemble.

Collectibility & Value

Availability is extremely limited because of the production count of approximately 100 units. Prices by condition vary significantly, but collectors note that functional hybrids command a premium far above standard Solina String Ensembles. A working unit in good cosmetic condition often reaches five-figure sums, thanks to the scarcity and the dual synthesis capability. Buyers should verify that both the string section and the Explorer lead section work. Repairs on the hybrid interface are complex and require specialized knowledge of both Eminent and ARP circuit designs.

Common failures mirror those of the Solina String Ensemble, particularly in the chorus circuit and power supply. The chorus ICs are known to fail, leaving a static string sound without the characteristic shimmer. Power supply capacitors age over decades, and the resulting voltage instability affects tuning across the divide-down oscillators. Service technicians observe that restoration can cost a lot, since specific analog components are needed for the Eminent section along with ARP-specific parts for the lead engine. Before buying, check the global tuning knob for smooth operation and make sure the Gate and Trigger outputs fire correctly, as these are critical for integrating the instrument into a modern modular setup.

Ownership quirks include the heavy weight of the wooden chassis and the heat from the analog power rails. The wood panels age well but can warp if stored in fluctuating humidity. Honest warnings suggest that unless the buyer has access to a technician familiar with 1970s Dutch analog organ circuitry, maintenance should be budgeted alongside the purchase price. It sounds gorgeous but it will try to catch fire if you don't recap it, a sentiment echoed by many long-term owners of similar vintage analog gear from this period.

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