ARP Explorer I (Model 2900) (1974–1978)
Analog monophonic synthesizer combining preset convenience with manual sound design, made in the USA.
Overview
The ARP Explorer I (Model 2900) is an analog monophonic synthesizer produced by ARP from 1974 to 1978. It bridges preset and manual synthesis, offering factory voices like flute, trumpet, and "lunar lander" while allowing full sound creation from scratch. Marketed as a preset synth, it operates as a hybrid with a streamlined 2600-style voice architecture in a Pro-Soloist form factor. It was ARP’s first non-preset single oscillator synthesizer and marked the company’s early effort to balance immediate playability with hands-on control. The synth features a 37-note synth-action keyboard and is constructed with a metal and wood case in black finish.
Specifications
| Production | 1974–1978 |
| Polyphony | Monophonic |
| Oscillator Type | VCO (4027-1 Voltage Controlled Oscillator module) |
| Filter | 4-pole, 24dB/octave low-pass ladder filter (4034 Moog Ladder Filter module), with resonance and self-oscillation |
| Envelope Generator | ADSR for filter and amplifier (common section) |
| LFO | Two LFOs: one with frequency adjustment and restart switch; second for vibrato with switch and frequency control |
| Waveforms | Sawtooth, square, pulse, fuzz (can be combined simultaneously) |
| Noise Source | Built-in pink noise |
| Controllers | Portamento, pitch bend (shared rotary knob) |
| Keyboard | 37-note, synth action |
| Audio Output | Mono analog: 1/4" (6.35mm) and original RCA high output, 1/4" low output; 1/4" jack modified as second high output in serviced units |
| Power | Internal power supply for 110V/220V, 50–60Hz |
| Country of Origin | USA |
| Preset Voices | Flute, trumpet, lunar lander |
Design
The ARP Explorer I uses a double-sided circuit board with the oscillator board identical to the ARP Little Brother and the 4027-1 VCO from the ARP 2600. It incorporates the 4034 Moog ladder filter from the Pro-Soloist, arranged in a four-step VCF structure. Waveforms can be combined simultaneously, and the filter enters self-oscillation at high resonance. The unit features 12 linear potentiometers (faders), where many reliability issues occur due to poor factory soldering, including lifted pads and broken traces. The silkscreen tends to fade over time, and tantalum capacitors are known failure points.
Context
The ARP Explorer I predates the ARP Axxe and ARP Solus and is a close relative of the Pro-Soloist. It represents ARP’s first real step in merging preset accessibility with manual synthesis, signaling a shift toward instruments that were both immediate and customizable. As part of the ARP lineup alongside the 2600, Odyssey, and Pro-Soloist, it is considered a cult-classic hybrid and a sleeper hit for players seeking ARP’s signature sounds without patch cables.
Market
A unit serviced in September 2023 received a full restoration including replacement of all 12 sliders, recapping the power supply, replacing tantalum capacitors with electrolytics, rebuilding the keyboard, calibrating with an oscilloscope, and modifying the output to make the 1/4" jack a second high output (reversible). Common repairs involve jumpering broken traces and using a continuity beeper and service manual for diagnostics. Collectors regard the Explorer I as rare and weird, often whispering about it “like it’s a lost chapter in synth scripture.”
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