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 that ARP built from 1974 to 1978. It sits between a preset synth and a manual one. It has factory voices like flute, trumpet, and "lunar lander," and you can still build a sound from scratch. It was marketed as a preset synth, but it works as a hybrid: a streamlined 2600-style voice architecture in a Pro-Soloist form factor. It was ARP’s first non-preset single oscillator synthesizer. The keyboard is a 37-note synth-action unit, and the case is metal and wood in a 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 Explorer I uses a double-sided circuit board. The oscillator board is identical to the one in the ARP Little Brother, and the VCO is the 4027-1 from the ARP 2600. The filter is the 4034 Moog ladder filter from the Pro-Soloist, in a four-step VCF arrangement. Waveforms can be combined at the same time, and the filter self-oscillates at high resonance. There are 12 linear potentiometers (faders), and that is where many of the reliability problems show up. The factory soldering was poor, which leaves lifted pads and broken traces. The silkscreen tends to fade over time, and the tantalum capacitors are known failure points.

Context

The Explorer I predates the ARP Axxe and ARP Solus, and it is a close relative of the Pro-Soloist. It was ARP’s first real step toward mixing preset accessibility with manual synthesis. It sat in the ARP lineup alongside the 2600, Odyssey, and Pro-Soloist. It is considered a cult-classic hybrid and a sleeper hit for players who want ARP’s signature sounds without patch cables.

Market

One unit serviced in September 2023 got a full restoration. All 12 sliders were replaced, the power supply was recapped, the tantalum capacitors were swapped for electrolytics, and the keyboard was rebuilt. It was calibrated with an oscilloscope, and the output was modified so the 1/4" jack is a second high output (reversible). Common repairs involve jumpering broken traces, and a continuity beeper and the service manual handle diagnostics. Collectors regard the Explorer I as rare and weird.

Similar items on eBay

No exact ARP 2900 listings are live right now — these searches show current ARP and similar vintage synth gear on eBay:

Search ARP 2900 on eBay Browse ARP synth gear on eBay

As an eBay Partner, we earn from qualifying purchases. This helps support our independent vintage technology research.