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Spectral Audio Neptune 2

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With the Neptune Mk2, Spectral Audio is again tickling out the best of the Analog Technique - three temperature stabilized Voltage Controlled Oscillators, the 24dB transistor cascade filter, the huge LFO range, its modulation flexibility, the envelopes and the transistor distorter section are speaking for itself.

Excellent technique in a 2 unit 19" rack case with deep blue front panel.

The basic principle of the Neptune II corresponds to classic subtractive analog synthesis which incorporates interconnection between a VCO, VCF, VCA, envelope generators and LFO.

To make the Neptune II suitable for MIDI, an additional MIDI to CV converter is added which converts the MIDI signals into analog control voltage signals. These control the VCOs, the filter, as well as the envelope generators. It is able to create Control Voltage (CV) for 5 octaves. However, the oscillators in the Neptune II are able to process up to 7 octaves.

The raw material for the sound is provided by the VCOs (Voltage Controlled Oscillators, known as OSC1..OSC3) in the form of a sawtooth or rectangular signal as well as the noise generator (for effects such as wind and thunder sounds). OSC2 is synchronized to OSC1 with the SYNC switch. The sound becomes especially interesting when the TUNE control of OSC2 is turned (or modulated by the LFO), resulting in the typical "Sync-Sound". By means of the external OSC input, other sources can also serve as raw material. The TUNE range is a good compromise between having a useful pitch range but still able to finely adjust the pitch.

The ring modulator multiplies the signals of the two OSCs. This significantly amplifies the beats (frequency difference).

Note: When the SYNC switch is switched on, no beats are developed and the ring modulator therefore has no effect.

The SLIDE control determines the glide time from one note to another and is valid for all OSCs.

Afterwards, the signal flows through the Voltage Controlled Filter (VCF), within which certain frequency ranges are suppressed. The lowpass filter allows low frequencies to pass and suppresses the high ones, the highpass filter lets high frequencies pass and suppresses the low ones. The frequency from which the signals are suppressed is called the limit or cut-off frequency. In the Neptune II, this is formed by various sources:

1. CUTOFF frequency control

2. ENV MOD control (the influence of the envelope curve on the cut-off frequency)

3. OSC3/LFO when the Cut-off target push switch is on


The KEYFOLLOW may be set to no KEYFOLLOW, 50% or 100%. It causes the cut-off frequency to increase on higher notes so that the audible frequency band always remains the same. Moreover the filter can be used as an oscillator, if the resonance is set to the maximum. The resonance forms a feedback of the output to the input of the filter and causes an amplification of the frequencies around the cut-off frequency. The Filter is adjusted for exact tone scale.

After the filter, the signal reaches the distorter circuit, which provides two different types of distortion: Fuzz distortion or clipping distortion, both known from (olden day) guitar effects units. Before the signal leaves the Neptune II, it arrives at the VCA (Voltage Controlled Amplifier). The input signal is here multiplied by the control signal formed by the Amp Envelope and the VOLUME potentiometer. The OSC3/LFO is particularly well designed in the Neptune II. The oscillator is either freely controllable or fixed to the MIDI to CV converter. The desired mode may be chosen using the FREERUN switch. Note:

When using the OSC3/LFO in LFO mode, the description at the OCTAVE switch does not apply. It is however possible to adjust a coarse frequency. Using its signal, the pitch from OSC1 and OSC2 and also the Cut-off frequency of the filter can be modulated. If the MIXER switch is on, the OSC3/LFO output is directly audible. In this case, the MODULATION pot controls the volume level. The rotary switch allows 5 different signal forms to be selected. Additionally, the OSC2 can be used as a modulation source. The MIDI SYNC switch allows the LFO to be synchronized to MIDI Clock.

The Envelope Generator determines the chronological sequence of the volume after receiving a ‘note-on’ command. The MIDI to CV converter then issues a gate signal (+5V) starting the sequence of the envelope generator. The gate signal remains active at +5V until the ‘note-off' command comes, i.e., when the key is released.

Technical Specifications
Type: Analog
Synthesis: Subtractive
Oscillators: 3
Waveforms: Pulse, Saw Up, Triangle, White Noise
Osc Modulation: Continuous Controller, Envelope, Input, Knob, LFO, Sync Hard
Envelopes: 1
Evelope Paramerters: Attack, Decay, Sustain, Release
Filters: 1
Types: 24dB Slope (4-pole), High Pass, Low Pass, Resonance
Filter Modulation: Envelope, Knob, LFO
LFO: 1
LFO Parameters: Noise, Sample & Hold, Saw Up, Triangle, Freerun
Polyphony & Tuning
Polyphony: 1
Tuning: Standard
Modes: Mono
Patches RAM: 1
Distorter and Fuzzer
Case: Rack
Rack Size: 19", 2U, Full
Controls: Buttons, Knobs, Switches, Modulation 1/4" Jacks
Audio Output Connections: 1/4" Phone Jack, Mono Out
Audio Output Count: 1
Inputs: 1 x 1/4" input
CV Ports: CV IN, CV OUT, Gate In, Gate Out
Year Released: 2003
Manuals & Documents

Product Links
Company Product Sites:
[+] www.spectralaudio.ch
Used Price: $550-$600 - convert
References & Sources

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