Keyboard

2 octave, may be stepped through 5 octave range from 16' to 1' using the "Range" switch. Debounced contacts. Max drift rate about ten minutes per semitone. "Drift" switch allows selected note to drift up or down once a key is released at about 1 octave per second. "Glide" variable 0 to 5 seconds. Front panel screwdriver adjustment "Tune" allows tuning of the synthesiser relative to other instruments over ±1/2 octave. Modulation by any or all of Sweep, VCO2/LFO, Envelope, Sample and Hold. High note priority.

VCO1

10Hz to 10kHz nominal range, hardwired to keyboard. Triangle output to VCA, ramp and squarewave outputs to VCF. Duty cycle of squarewave variable from 50% to 10% either manually or by VC02/LFO. May be switched off allowing VC02 or Noise to be used alone.

VCO2/LFO

VCO mode: 10Hz to 10kHz nominal range. Frequency may be manually set to any multiple of VCO1 frequency. Accurate tracking over entire range of keyboard. Triangle output to VCA; rising ramp, falling ramp or squarewave to VCF. Squarewave duty cycle manually variable from -10% through 5O% to +10%. Level control on output. Ring mod mode: Switch disconnects audio outputs but LFO modulation switches allow frequency modulation of keyboard, VC01 shape, VCF, VCA. In either mode, independent modulation allows pitch bending relative to VC01 by any of sweep, envelope, sample and hold. LFO mode: 0.1 Hz to 30Hz nominal range, manually variable. Manual level control, triangle, rising ramp, failing ramp and squarewave modulation via output switches to keyboard, VC01 shape, VCF, VCA. Modulation of LFO frequency by sweep, envelope, sample and hold.

Sub Octaves

Two divide-by-two circuits may be used to provide either an octave below VC01 frequency and an octave below that, or an octave below each of VC01 and VC02, switchable. Outputs: squarewave to VCF.

Noise

White noise source with level control. Output to VCF.

Sequencer socket

Keyboard output voltage 0.35 volts⁄octave. Trigger output voltage 9 volts positive, input requirements 0.35 volts⁄octave to keyboard, 9 volts positive trigger to envelope.

Envelope

Attack and release times variable 0 to 10 seconds. ADSR switch adds additional percussive attack. Triggered either from keyboard, or LFO as long as a key is depressed. Repeat switch causes the envelope shaper to retrigger itself, with a repeat time equal to the sum of the attack and release times. Sustain operates in three modes: "Manual" means the envelope attacks and remains high as long as a key is depressed (like an organ); "Auto" puts it into single shot mode so that depressing a key produces one attack and release cycle. The envelope is then only retriggered by re-pressing the same key or depressing a higher key. "Hold" produces a continuously audible output about half maximum volume - pressing a key then adds the envelope shape to this constant level bringing the output of the VCA up to maximum. The positive-going envelope is hardwired to VCA, positive and negative envelopes are available via the level control for modulation of any or all of keyboard, VCO2⁄LFO, VCF.

VCF

State variable filter with manual control of roll-off frequency. Outputs: switchable low pass or band pass to VCA. Manual "Q" control adjusts size of resonant peak at roll-off frequency. Min roll-off: 6dB per octave, max roll-off: 50dB per octave. Modulation of roll-off frequency by keyboard, envelope, sweep, VC02/LFO, sample and hold.

VCA

Controls output volume of synthesiser. Max attenuation: —60dB min. Max output level lOOmV into 10kΩ via master volume control on rear panel.

Sample and Hold

Analogue memory samples instantaneous output voltage from VCO2/LFO each time envelope ends. Output to thumbwheel.

Sweep

Manual control producing variable positive or negative d.c. control voltage with zero dead band at centre. Output to thumbwheel.

Thumbwheel

Manual level control. Modulation depths may be preset using sweep and VC02/LFO level controls, then introduced manually using the thumbwheel. Inputs: sweep, VC02/LFO or sample and hold. Output to keyboard, VC02/LFO or VCF.

Power Amp

Output 2 watt into 8Ω nominal.

Component List

Resistors       
R110kR52100kR8410kR11810k
R2680RR53,R54100RR858k2R119,R120??
R3 to R26 (2%)680RR55,R56100kR864k7R121??
R271k2R574k7R8710kR12233k
R281MR5833kR881kR1233M9
R2933kR59100kR8910kR1246k8
R301kR60,R6110kR9015kR125,R12647k
R31,R3210MR62,R6310MR911kR12733k
R33,R3415kR64,R6547kR92220RR128,R129100R