Spectral Audio Neptune

Spectral Audio Neptune Image
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The Neptune is an all-analog mono-synth with built-in MIDI and CV/Gate features in a 2-space rack-mount module. It features three true analog oscillators for a very fat Moog-type sound, and even has a Moog-type cascade filter to match! And in truly classic analog fashion, all parameters and controls are available from the knobs and switches on the front panel in an intuitive and clearly labeled layout - bringing old-school analog synthesis to the modern MIDI studio.

The Neptune is actually a lot like the ProTone, except that the Neptune achieves its third VCO by substituting the LFO as an audible oscillator (Osc 3 can be switched between LFO--slow--and Oscillator Mode--fast) and by adding a dedicated ADSR envelope to the 24dB/oct cascade filter. The Neptune also includes an audio input for processing external signals through its filter and LFO. Like the ProTone, it features both MIDI I/O and CV+Gate I/O and can handle MIDI-to-CV+Gate conversion (across a 5 octave range), making it an ideal synth for old-school and modern MIDI studios. It also features MIDI controlled filter cutoff and modulation control as well as velocity sensitivity. The original Neptune model debuted in 1999 and came in Violet, Silver or Gold colored panels.

Spectral Audio Neptune II Image

Neptune 2

In 2003 the updated mkII or Neptune 2 was released. Improvements included a cool new look, smoother pots, soft touch knobs, higher efficiency 5mm LEDs, 2.2mm travel push switches for optimal optical feedback, a Key-follow switch has been added, a better White Noise generator, a volume knob, a power switch, new PWM on Square Wave on Osc1, 2 or 3, Osc3 can Sync with Osc1 or Osc2, faster envelopes, and increased tuning range for all three oscillators.

The Neptune models represent a truly analog synth with an all analog signal path - nothing digital - which unfortunately, also means no patch memory storage. But it's such a breeze to use, and with every knob available, it's truly a synth tweaker's machine, capable of fat bass and synth sounds to weird bubbly and resonant noises. Yet despite its MIDI capability, the knobs do not transmit MIDI data for control of real-time data in to a sequencer. It does, however, respond to MIDI controller data for the filter cutoff, modulation, portamento, sustain and velocity. There is a Learn button for MIDI Channel and Reference note and the MIDI Thru signal is regenerated, not amplified, for a reliable through-put. The Neptunes are definitely unique, their sound is authentic, and their cost is incredibly reasonable. They make an excellent alternative to older vintage synths.

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Demos & Media

Spectral Audio Neptune
Spectral Audio Neptune 2
Audio Clip 1 Demo bass and synth sounds. From Future Music CD issue 85.


Polyphony - Monophonic (Highest or last note priority)
Oscillators - 3 very stable VCOs; 1 & 2 offer Sawtooth and Pulse Waves; VCO 3 can be switched between LFO and Sub Oscillator Modes; White Noise Generator; Ring Modulation and Sync Features for VCO 1 & 2 (mkII adds sync for VCO 3)
LFO - 5 Shapes (Sawtooth, Triangular, Rectangular, Random and Noise); VCO 2 can also be a Modulation Source, LFO MIDI Clock Sync; 4 Modulation targets: VCO 1 and 2, Cutoff and Mixer
Filter - 24 dB precision cascade Filter with Highpass and Lowpass Modes with dedicated ADSR with Positive or Negative Modulation (mkII adds Key-follow switch 0% - 50% - 100%).
VCA - ADSR Envelope
Effects - Distortion and 'Fuzzer' Effect; Slide Function, switchable by MIDI Controller 65 (Portamento)
Memory - None
Keyboard - None
Arpeg/Seq - None
Control - MIDI IN/THRU / CV+Gate (switchable between IN or OUT)
Date Produced - 1999 mk1 / 2003 mk2


Images from Spectral Audio and The Synthesizer Network

Reviewed August 2008.