Grove Audio GMS-302 User manual

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GMS-302 Dual Precision Voltage
Controlled Oscillator
PRELIMINARY OPERATION MANUAL
Ver. 1.0 –June 25, 2021
Grove Audio LLC
Copyright 2021 –All Rights Reserved

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INTRODUCTION
The GMS-302 Dual VCO contains two full-function voltage controlled oscillators in a 2MU or 4 ¼ inch Moog
compatible module. Each oscillator supplies a number of simultaneous waveform outputs as well as a Wave
output that allows selecting one of five waveforms to be sent to a separate output jack. The Wave output also
includes a voltage controlled amplifier to scale the output waveform under external voltage control.
Each core is built on a temperature compensated triangle wave oscillator that includes an exponential current
converter to implement standard 1 volt per octave control over the output frequency. The oscillator will track a
control voltage range of 10 octaves permitting frequency control over the entire audio range from sub-audible to
almost 20kHz.
Three modulation options are provided, linear and exponential FM modulation and a pulse output with pulse width
modulation. Panel attenuators allow the amount of modulation to be controlled.
FREQUENCY CONTROLS
A variable frequency control and a calibrated range switch are included to set the initial frequency that is
produced when no external modulation is applied. The calibrated range switch allows the initial frequency to be
set to one of five possible octave base frequencies. The range switch includes an LFO position that permits
generating very slow waveforms for modulation tasks. The variable frequency control offers a range of plus or

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minus two octaves.
FM MODULATION INPUTS
Linear and Exponential FM modulation inputs, in addition to the 1V/Octave input are provided. There is an
attenuator to control the depth of modulation that occurs. The linear FM input has switch selectable AC or DC
coupling that simplifies using the input when doing FM synthesis.
PULSE WIDTH MODULATION INPUTS
A variable pulse width control sets the initial duty cycle of the pulse output wave. Center position of the control will
produce a 50% duty cycle. The range of the control varies from 0 to 100%. The initial duty cycle can be varied by
applying a modulation input to the PWM input. The input voltage can be scaled using a panel attenuverter control.
The modulation input voltage can be either an AC or DC signal.
OSCILLATOR EXTERNAL SYNC INPUTS
Each oscillator includes an external sync input. A panel switch determines the type of synchronization that will
occur. The three position switch selects hard sync, soft sync or no external sync. Hard sync resets the current
waveform immediately to zero. This type of sync can be used to keep multiple oscillators in phase or for resetting
long period waveforms to a known starting point. Soft sync resets the oscillator to zero if the oscillator is within a
certain range of starting the next cycle normally. This type of sync is good for locking oscillators that are running
at octave multiples.
SIMULTANEOUS WAVEFORM OUTPUTS
Four waveforms are continuously available on the panel. These are the SINE wave, the TRIangle wave, the
SAWtooth wave, and the PULSE wave.
WAVE OUTPUT
The WAVE output has a selector switch that routes one of five waveforms, SINE, TRI, SQUARE, SAW or PULSE
to the input of an internal voltage controlled amplifier. The output of the amplifier appears on the WAVE output.
The amplifier has a linear control function so applying a 0 to 5 Volt control voltage to the AMP CV input will vary
the output waveform from 0 to approximately 5 Volts peak to peak. Going beyond 5 Volts will actually amplify the
waveform up to about twice the normal output level.
GENERAL INFORMATION
The compact thin profile of the oscillator allows use in shallow mounting racks and having two oscillators
contained within one module permits reducing the size of multiple oscillator instruments. Four full function
oscillators will fit in the space normally occupied by two conventional oscillators allowing for more complex
patches.
BASIC FUNCTIONS

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TECHNICAL SPECIFICATIONS GMS-302
Each Channel
Voltage Scale
1 Volt/Octave - .0833
Volts/Semitone
MIDI Note Range
Note number 0 - 127
produces -4.0 V to +6.0 V
0 V = MIDI Note #48 = C4
(starting note for zero
volts is presettable)
D/A Converter Output
16 Bits; full-scale range
+-10 V
Gate/Trigger Output
0 - +5 V Gate width:
duration of note Trigger
width: 25 msec.
Module Power
+15 Volts 25 mA., -15
Volts 25 mA., +5 Volts
100 mA

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Module Size
Panel height - 8.75
inches (222 mm); Panel
width –4.25 inches (108
mm); Depth (behind
panel) 2.0 inches (51
mm)

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GMS-302 CALIBRATION ADJUSTMENTS