GRP Synthesizer A1 User manual

Grp A1 - Owner’s Manual
Grp Synthesizer®
A1 - Owner’s Manual
www.grpsynthesizers.it [e-mail]
www.grpsynthesizer.it
1
Grp Synthesizer A1
®
1V/Oct IN GATE IN CV IN PWM CV IN FLT CV IN VCA EXT IN VCF OUT EG OUT LFO 2 OUT PHONES MAIN OUTVCO OUT
010 010
b #
010 010
010 010 010
010 010 010 010 010
010 010 010 010
010
010
010
MIDI INTERFACE VCO
MIDI TO CV KEY VEL FEG
GLIDE BEND AMT
8'
4'
16' SAW
SQR
TRI
LFO 1
LFO 2
EG
MAN
LFO 1
TUNE
PWM FM AMT
HOLD
FILTER EG
GATE + REL
MAIN OUT
VCA
NOISE LEVELVCO LEVEL SUB LEVEL
OCTAVE WAVE
DISABLE
ACT
FMTRKRESONANCEFREQUENCY DIST
LFO 1
LFO 2
18 dB VCF
DECAY RELEASESUSTAINATTACK EG AMT
SLOW
RATE
MID
RATE
FAST
SHAPE
RND
SLOW
MID
FAST
SHAPE
LFO 1-S&H
LFO 2
ENVELOPE GENERATOR
MID
SLOW
FAST
010
LFO 1 OUT

Grp A1 - Owner’s Manual
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Grp A1 - Owner’s Manual
Contents
1. Welcome
2. Safety Rules
3. Connections
3.1. MIDI Data Received
3.2. Choosing MIDI Channel
4. The Grp A1 Synthesizer
4.1. MIDI INTERFACE
4.1.1. MIDI TO CV ENABLE
4.1.2. KEY VEL FEG ENABLE
4.1.3. GLIDE
4.1.4. BEND AMT
4.2. VCO
4.2.1. VCO - Panel Controls
4.2.1.1. TUNE
4.2.1.2. OCTAVE
4.2.1.3. WAVE
4.2.1.4. PWM
4.2.1.5. LFO1/MAN
4.2.1.6. LFO1 / EG / LFO2
4.2.1.7. FM AMT
4.2.2. VCO - Audio and Control Connections
4.2.2.1. 1v/Oct IN
4.2.2.2. CV IN PWM
4.2.2.3. VCO OUT
4.3. MIXER
4.3.1. MIXER - Panel Controls
4.3.1.1. VCO
4.3.1.2. SUB
4.3.1.3. NOISE
4.3.2. MIXER - Audio Connections
4.3.2.1. EXT IN
4.3.3. MIXER - Working with internal Jumpers
4.4. 18 dB VCF
4.4.1. 18dB VCF - Panel Controls
4.4.1.1. FREQUENCY
4.4.1.2. RESONANCE
4.4.1.3. DIST
4.4.1.4. TRK
4.4.1.5. FM
4.4.1.6. LFO 1/LFO2
4.4.1.7. EG AMT
4.4.2. 18 dB VCF - Audio and Control Connections
4.4.2.1. CV IN FLT
4.4.2.2. VCF OUT
4.5. ENVELOPE GENERATOR
4.5.1. ENVELOPE GENERATOR - Panel Controls
4.5.1.1. ATTACK
4.5.1.2. DECAY
4.5.1.3. SUSTAIN
4.5.1.4. RELEASE
4.5.1.5. MID / FAST / SLOW
4.5.2. ENVELOPE GENERATOR - Control
Connections
4.5.2.1. GATE IN
4.5.2.2. EG OUT
4.6. VCA
4.6.1. VCA - Panel Controls
4.6.1.1.GATE+REL / HOLD / FILTER EG
4.6.1.2. MAIN OUT
4.6.2. VCA - Audio and Control Connections
4.6.2.1. CV IN VCA
4.6.2.2. MAIN OUT
4.6.2.3. PHONES
4.7. LFO 1 - S&H
4.7.1. LFO 1- S&H - Panel Controls
4.7.1.1. RATE
4.7.1.2. MID/FAST/SLOW
4.7.1.3. SHAPE
4.7.1.4. TRIANGLE / RND / PULSE
4.7.2. LFO 1 - S&H - Control Connections
4.7.2.1. LFO 1 OUT
4.8. LFO 2
4.8.1. LFO 2 - Panel Controls
4.8.1.1. RATE
4.8.1.2. MID / SLOW / FAST
4.8.1.3. SHAPE
4.8.1.4. TRIANGLE / PULSE
4.8.2. LFO 2 - Control Connections
4.8.2.1. LFO 2 OUT
5. FRONT PANEL CONNECTIONS
5.1. INPUTS
5.2. OUTPUTS
6. REAR PANEL CONNECTIONS
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3

Grp A1 - Owner’s Manual
1. Welcome
Thank you for purchasing the Grp A1 Synthesizer. The instrument is equipped with a powerful audio
oscillator, a sub oscillator and a noise generator that together with a possible external signal can be treated
with an aggressive resonant low-pass filter at -18 dB / Oct with personal and recognizable sound.
It is possible to use an Envelope Generator, a pair of Low Frequency Oscillators (with Sample & Hold
function) to control the behavior of the synthesizer.
Grp A1 Synthesizer, which manages MIDI and analog CV / Gate, can be powered with any USB Type-C
Power Pack or USB port capable of delivering +5V @ 2.5A.
NOTE: While Grp A1 Synthesizer has an effective absorption of 750 mA, some cheap USB power supplies
may not guarantee - despite what is declared by the respective manufacturers - sufficiently solid energy to
feed synthesizer on a regular basis. The same could happen with the USB ports of poorly energy-equipped
laptops.
If necessary, it is recommended to use a powered USB hub, using it between the laptop and the Grp A1
Synthesizer.
Under no circumstances should Grp Synthesizer be held responsible for any malfunctions.
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Grp A1 - Owner’s Manual
2. Safety Rules
Please read the instructions here carefully. You must always follow the safety rules when working with
electrical equipment, for your health and that of your precious equipment.
OPERATING CONDITIONS
• Do not use this synthesizer in potentially hazardous environments and near water (swimming
pools, bathrooms, sinks, places with a lot of humidity).
• Never use synthesizer in very dusty and dirty places.
• Never place the synthesizer near heat sources, such as radiators or stoves.
• Do not expose the instrument directly to sunlight. Ultraviolet rays can change colors.
• Do not expose the appliance to strong mechanical vibrations.
• Do not throw away the original packaging: they can be useful to safely ship the unit.
POWERING
• Your Grp A1 synthesizer can be powered by any Power Bank or USB power supply capable of
delivering +5V voltage (according to USB standards) with 2.5 A.
See what already reported at section 1. Welcome on page 4 of this Owner’s Manual.
• The unit can be powered by a USB port on the computer; in this case, you can also take
advantage of MIDI over USB capabilities.
See what already reported at section 1. Welcome on page 4 of this Owner’s Manual.
• Disconnect the power supply if you do not have to use the appliance for a long time.
• When disconnecting the power, grab the Power Bank or power supply securely, avoiding pulling
the cord.
OPERATIONS
• Even if you are a rockstar, NEVER place bottles or glasses with liquids near the synthesizer.
• The synthesizer must be placed on a solid surface.
• The synthesizer can produce VERY loud sounds; Avoid hurting your ears.
CORRECT USE OF THE INSTRUMENT
• This synthesizer is designed exclusively for the production of audio signals. Any other use is
prohibited and violates the warranty of Grp Synthesizer. Grp Synthesizer is in no way responsible
for damage caused by improper use of the device.
While Grp A1 Synthesizer has an effective absorption of 750 mA, some cheap USB power supplies may not
guarantee - despite what is declared by the respective manufacturers - sufficiently solid energy to feed
synthesizer on a regular basis. The same could happen with the USB ports of poorly energy-equipped
laptops.
If necessary, it is recommended to use a powered USB hub, using it between the laptop and the Grp A1
Synthesizer.
Under no circumstances should Grp Synthesizer be held responsible for any malfunctions.
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5

Grp A1 - Owner’s Manual
3. Connections
After obtaining a USB Type-C compatible power supply capable of delivering +5V @ 2.5A, connect it on the
rear panel to the 2.5A input marked with the USB symbol. The effective synthesizer absorption is 750 mA.
See what already reported on Section 1. Welcome in page 4 of this Owner’s Manual.
The connector supports MIDI-Over-USB protocol with Mac/PC. The synthesizer is seen by the computer as a
Grp A1 peripheral and can execute Note On/Off & Pitch Bend commands sent by your DAW on the
instrument's MIDI Channel (see below).
If necessary, use the MIDI IN port to drive the Grp A1 with a MIDI Master Keyboard or other external
controller equipped with MIDI 5-pin DIN.
Alternatively, you can control the instrument using the analog connections on the lower end of the front
panel:
• 1V/Oct IN. Connect to this input the necessary CV voltage drive the pitch of the VCO internal
oscillator.
• GATE IN. Connect to this input the GATE voltage (0/+5V) necessary to activate and articulate the
internal Envelope Generator.
Connect the MAIN OUT output to your amplification system. The MAIN OUT command (in the VCA section)
controls the audio out level.
Although a 1/8" TRS cable can be used, the instrument is designed to work with unbalanced TS-Tip /
Sleeve 1/8" connections.
You can use the PHONES output to listen to the instrument on headphones. Again, the MAIN OUT
command controls the listening volume.
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Grp Synthesizer
2.5A
MIDI IN
®
Grp Synthesizer
MODEL :
SUPPLY:
Analog Synth
WATT: MADE IN ITALY
A1
3.5
USB 2.5A
S.N. :

Grp A1 - Owner’s Manual
3.1. MIDI Data Received
Grp A1 synthesizer receives MIDI data for:
• Note On/Off with Key Velocity (the dynamic controls the Filter Envelope Amount).
• Pitch Bend.
3.2. Choosing MIDI Channel
On powering on, check the position of the MIDI TO CV switch in the MIDI INTERFACE module:
•Power on with MIDI TO CV switch in DISABLE position. If the switch is in the DISABLE (down)
position, the ACT LED blinks indicating that the instrument is waiting to receive any message sent
over the MIDI Channel to tune to.
To tune the synthesizer to the desired MIDI channel, you need:
•Return the MIDI TO CV switch to the ENABLE (up) position for normal operation.
•Press a MIDI note or send any MIDI message from the control source; the ACT LED blinks
faster indicating the reception of MIDI data and then turns off waiting for the normal codes
received.
Now, the Grp A1 is tuned to the desired MIDI channel and can be used normally.
• Power on with MIDI TO CV switch in ENABLE position. If the instrument is turned on with the
switch in the ENABLE (upward) position, the machine remains set to the previously selected MIDI
Channel. The ACT LED lights up only when the instrument receives MIDI data, indicating the MIDI
reception activity of the received commands.
NYou do not need to repeat the MIDI tuner procedure every time you turn on the instrument.
•If you want to change MIDI Channel with the synthesizer already turned on, simply switch the
MIDI TO CV switch first to the DISABLE position (down) and then to the ENABLE position
(upwards).
The ACT LED starts blinking indicating that the instrument is waiting to receive a new MIDI
Channel. After the Channel is assigned, the ACT LED stops blinking and lights up only to indicate
the reception of MIDI traffic in progress.
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Grp A1 - Owner’s Manual
4. Grp A1 Synthesizer
The Grp A1 monophonic synthesizer can be used as a stand-alone musical instrument or can be used to
filter external signals within the Low Pass 18dB VCF resonant circuit. The three internal audio sources (VCO,
SUB and NOISE) guarantees timbre power and ease of use. With the two Low Frequency Oscillators - LFOs
(the first, integrates an S&H Sample & Hold) and with the ADSR Envelope Generator, it is possible to sculpt
the cyclic or transient modulation behavior.
It is possible to obtain independent articulations of VCF and VCA by choosing for the latter one of the
behaviors FILTER EG, GATE + REL, HOLD.
The instrument can be removed from your cabinet to be easily installed in any EuroRack modular system; it
is possible to power it using the normal flat cables supplied with EuroRack systems.
Inside, on the back of the components board, you can locate the Jumper with which you change the
sensitivity of the EXT INPUT.
Below is a description of the individual controls and connections available for each section of the tool.
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WAVE
SWITCH
CV OUT 1V/Oct
PITCH BEND
VELOCITY
ADSR
GATE IN 0/5V
AT TAC K
DECAY
SUSTAIN
RELEASE
FM
AMT
PITCH BEND
AMT
PW M
AMT
LFO 1
LFO 2
EG
MAN
SAW
TRI
SQ R
FM AMT
LFO 1LFO 2
FM
SWITCH
RESONANCE
MIX
WHITE
NOISE
SU B
VCO
NOISE
SUB VCO
- 1 Oct.
ADSR OUT
EG AMT
LFO1
WAVE SWITCH
S&H OUT
FM
SWITCH
RATE SHAPE
RND
CLOCK IN
RATE SHA PE
S&H IN
VCF
TIME
GLIDE
MIDI
INTERFACE
GATE OUT 0/5V
DIST
VCA MODE
SWITCH
CV IN VCA
S&H 1
LFO 2
VCA
VCA
MASTER OUT
DIST AMT
vco
LFO 1
LEFT
RIGHT
FR EQU ENCY
KYBD TRK
FILTER O UT
OCTAVE
SWITCH
8'16' 4'TUNE
PWM
SWITCH +5V
MIDI IN
MIDI USB
LED A CT
KEY VEL FEG
SWITCH
+5V
LFO2
WAV E SWITCH
LFO 1
MAN
MAIN OUT
FILTER EG
HOLD
GATE + RE L
PHONES OUT
CV IN 1V/Oct
JACK PANEL
GATE IN
JACK PANEL
EXT IN
JACK PANEL

Grp A1 - Owner’s Manual
4.1 MIDI INTERFACE
The MIDI INTERFACE section manages the reception and interpretation of MIDI codes that reach the A1
synthesizer indifferently on the DIN MIDI IN or USB connector on the rear panel.
4.1.1. MIDI TO CV
The switch enables or disables MIDI reception; reception is active with the
switch in the ENABLE (upward) position.
In the other case, when the switch is in the DISABLE position, the instrument
can only be controlled via CV/Gate.
The ACT LED lights up in response to receiving a MIDI code. Please refer to
section 2.2. CHOOSE THE MIDI CHANNEL to check the possible operating
conditions of the LED and their meanings.
4.1.2. KEY VEL FEG
The command activates or disables the reception of the MIDI Key Velocity applied to the control of the
Filter Envelope Amount; in this way, by varying the executive dynamics, it is possible to obtain a greater or
lesser opening of the Low pass Filter.
4.1.3. GLIDE
Adjusts the Glide Time value applied to CV 1V/Oct and/or notes received via MIDI/USB. Time Range is
between 0 and 1.5 Sec/Oct.
4.1.4. BEND AMOUNT
The command sets the the MIDI Pitch Bend range. The value is between 0 and 12 semitones in the positive
and negative direction.
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Grp Synthesizer A1
®
1V/Oct IN GATE IN CV IN PWM CV IN FLT CV IN VCA EXT IN VCF OUT EG OUT LFO 2 OUT PHONES MAIN OUTVCO OUT
010 010
b #
010 010
010 010 010
010 010 010 010 010
010 010 010 010
010
010
010
MIDI INTERFACE VCO
MIDI TO CV KEY VEL FEG
GLIDE BEND AMT
8'
4'
16' SAW
SQR
TRI
LFO 1
LFO 2
EG
MAN
LFO 1
TUNE
PWM FM AMT
HOLD
FILTER EG
GATE + REL
MAIN OUT
VCA
NOISE LEVELVCO LEVEL SUB LEVEL
OCTAVE WAVE
DISABLE
ACT
FMTRKRESONANCEFREQUENCY DIST
LFO 1
LFO 2
18 dB VCF
DECAY RELEASESUSTAINATTACK EG AMT
SLOW
RATE
MID
RATE
FAST
SHAPE
RND
SLOW
MID
FAST
SHAPE
LFO 1-S&H
LFO 2
ENVELOPE GENERATOR
MID
SLOW
FAST
010
LFO 1 OUT

Grp A1 - Owner’s Manual
4.2. VCO
The VCO (Voltage Controlled Oscillator) is the main sound source of the synthesizer; It produces different
waveforms (with a different harmonic content) and can be tuned to the desired frequency. It is possible to
modulate the symmetry of the square wave and the pitch of the oscillator. The VCO oscillator signal can be
enhanced using the available SUB Oscillator.
4.2.1. VCO - Panel Controls
Below is a description of the panel commands.
4.2.1.1 TUNE
Controls the oscillator’s pitch.
The command has range equal to +/-1 octave (with zero in
the center position) and its value is added to control
received through MIDI IN / USB or through analog
connection 1V / Oct IN.
4.2.1.2. OCTAVE
Adjust the octave of the VCO by choosing between 16' (an octave lower than the note played), 8' (the same
octave as the note played), 4' (one octave above the note played).
4.2.1.3. WAVE
Selects the oscillator’s waveform. SAW, TRI and SQR waves are available; the latter can be adjusted in
symmetry/pulse width/duty cycle using PWM control (see below).
4.2.1.4. PWM
The control sets the square/pulse wave symmetry. Depending on the position chosen with the LFO1/MAN
switch, the control will act as a true symmetry value between 0 and 50% (switch in MAN position) or as
Amount for the modulation produced by the Low Frequency Oscillator LFO 1 (switch in position LFO 1).
The PW-Pulse Width symmetry can also be controlled through an external modulation signal connected to
the unprocessed CV input in PWM.
4.2.1.5. LFO1 / MAN
The switch allows you to choose which modulation source is applied to the PW-Pulse Width symmetry of
the square wave. In LFO position 1, the first Low Frequency Oscillator (and integrated S&H functions) will
act on symmetry; in the MAN(ual) position, it becomes possible to adjust the symmetry value by hand
acting directly on the PWM rotary control.
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Grp A1 - Owner’s Manual
4.2.1.6. LFO1 / EG / LFO2
The switch chooses the modulation source that is applied to the pitch of the oscillator into range set
through FM AMOUNT control. With the three switch positions, you can choose: LFO 1 (the modulating
signal produced by LFO 1 - and internal S&H), EG (the ADSR Envelope Generator), LFO 2 (the modulating
signal produced by LFO 2).
4.2.1.7. FM AMOUNT
The control sets the modulation index applied to the oscillator frequency.
4.2.2. VCO - Audio and Control Connections
Below, the description of the connections (audio and control) on the front panel related to the VCO
oscillator.
4.2.2.1. 1v/Oct IN
The connection is designed to receive 1V/Oct control voltages from keyboards, sequencers or other
external CV sources.
4.2.2.2. CV IN PWM
The connection allows remote control of the PW symmetry of the SQR wave. The control input is not
processed, so any attenuations on the external control signal should be provided externally.
4.2.2.3. VCO OUT
The connection makes the audio signal produced by the oscillator available for any external use (or for
audio rate modulation); the signal is not attenuated and comes out with a 10V p-p level.
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Grp A1 - Owner’s Manual
4.3. MIXER
The MIXER receives and balances the three signals simultaneously available in the A1 synthesizer.
4.3.1. MIXER - Panel Controls
Below, the description of the MIXER panel commands.
4.3.1.1. VCO LEVEL
The control adjusts the output volume of the Voltage Controlled Oscillator. If you choose SQR wave and the
PWM symmetry of the SQR wave is set on extreme values, the signal produced by the oscillator may not be
audible.
4.3.1.2. SUB LEVEL
The control sets the volume of the Square wave produced by frequency division at a low octave distance
from the VCO signal.
4.3.1.3. NOISE LEVEL
The control sets the volume of the White Noise Generator available into A1 Synthesizer.
4.3.2. MIXER - Audio Connections
Below, the description of the audio connections related to the MIXER present on the front panel of the
instrument.
4.3.2.1. EXT IN
It is possible to exploit a fourth signal coming from the outside and possibly connected to the EXT IN
connection. In this case, it is necessary to provide externally for its volume adjustment.
Inside the instrument, on the back of the components board, there is a Jumper for select the sensitivity of
the EXT IN connection.
• No Jumper. The circuit accepts signals up to 10V p-p.
• Jumper in MID position. The circuit accepts signals up to 5V p-p.
• Jumper in HI position. The circuit accepts signals up to 1V p-p.
Grp A1 Synthesizer is factory shipped with Jumper Jumper in MID position.
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Grp Synthesizer A1
®
1V/Oct IN GATE IN CV IN PWM CV IN FLT CV IN VCA EXT IN VCF OUT EG OUT LFO 2 OUT PHONES MAIN OUTVCO OUT
010 010
b #
010 010
010 010 010
010 010 010 010 010
010 010 010 010
010
010
010
MIDI INTERFACE VCO
MIDI TO CV KEY VEL FEG
GLIDE BEND AMT
8'
4'
16' SAW
SQR
TRI
LFO 1
LFO 2
EG
MAN
LFO 1
TUNE
PWM FM AMT
HOLD
FILTER EG
GATE + REL
MAIN OUT
VCA
NOISE LEVELVCO LEVEL SUB LEVEL
OCTAVE WAVE
DISABLE
ACT
FMTRKRESONANCEFREQUENCY DIST
LFO 1
LFO 2
18 dB VCF
DECAY RELEASESUSTAINATTACK EG AMT
SLOW
RATE
MID
RATE
FAST
SHAPE
RND
SLOW
MID
FAST
SHAPE
LFO 1-S&H
LFO 2
ENVELOPE GENERATOR
MID
SLOW
FAST
010
LFO 1 OUT

Grp A1 - Owner’s Manual
4.4. 18dB VCF
The 18dB VCF - Voltage Controlled Filter allows you to sculpt in real time the harmonic content of the
sound generated by the synthesizer. When controlled with the transient ADSR Envelope Generator, or under
the cyclic control of the LFO - Low Frequency Oscillator, it gives expressiveness and intensity to the sound.
The 18dB circuit offers a different timbre, less dark than to the classic 24 dB and, at the same time,
produces a more acidic signal than the equally classic 12 dB if adjusted to high Resonance values.
4.4.1. 18dB VCF -
Panel Controls
Below, the description of the 18 dB
Filter commands on the operation
panel.
The picture also reproduce, for
convenience, the commands of the
ADSR Envelope Generator which we
will discuss later.
4.4.1.1. FREQUENCY
Adjusts the Cutoff Frequency of the filter, which defines the limit of the high harmonics let through.
In addition to the controls received from the ADSR Envelope Generator and the FM by LFO 1/LFO 2, it is
possible to control the FREQUENCY through the Keyboard Tracking managed with the TRK command
(processed based on what was received via MIDI and / or the voltage received at the analog input 1V / Oct
IN). Still, it is possible to connect an external control source (unprocessed) using the FLT CV input.
As you can imagine, if you exaggerate with the simultaneous amount of control voltage, the FREQUENCY
command will be difficult to manage.
4.4.1.2. RESONANCE
It sets the amount of signal in recirculation making progressively more emphasized and then acid the timbre
produced by the filter itself. Extreme values of RESONANCE can bring the filter into self-oscillation
generating a sine wave of frequency equal to the value of Cutoff FREQUENCY.
In this case, it is possible to play the RESONANCE using an accurate adjustment of the TRK control
together with the MIDI values and the external CV CONTROL IN FLT.
4.4.1.3. DIST
Adjusts the amount of saturation applied to the output audio signal to the filter.
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Grp Synthesizer A1
®
1V/Oct IN GATE IN CV IN PWM CV IN FLT CV IN VCA EXT IN VCF OUT EG OUT LFO 2 OUT PHONES MAIN OUTVCO OUT
010 010
b #
010 010
010 010 010
010 010 010 010 010
010 010 010 010
010
010
010
MIDI INTERFACE VCO
MIDI TO CV KEY VEL FEG
GLIDE BEND AMT
8'
4'
16' SAW
SQR
TRI
LFO 1
LFO 2
EG
MAN
LFO 1
TUNE
PWM FM AMT
HOLD
FILTER EG
GATE + REL
MAIN OUT
VCA
NOISE LEVELVCO LEVEL SUB LEVEL
OCTAVE WAVE
DISABLE
ACT
FMTRKRESONANCEFREQUENCY DIST
LFO 1
LFO 2
18 dB VCF
DECAY RELEASESUSTAINATTACK EG AMT
SLOW
RATE
MID
RATE
FAST
SHAPE
RND
SLOW
MID
FAST
SHAPE
LFO 1-S&H
LFO 2
ENVELOPE GENERATOR
MID
SLOW
FAST
010
LFO 1 OUT

Grp A1 - Owner’s Manual
4.4.1.3. TRK
Adjust the Keyboard Tracking applied to the Cutoff FREQUENCY. In position 10, the control respects the
1v/Oct ratio, allowing the tempered execution with the RESONANCE possibly brought in self-oscillation.
4.4.1.4. FM
The command adjusts the intensity of the frequency modulation applied to the Cutoff FREQUENCY value.
You can choose two control sources using the nearby LFO 1 / LFO 2 switch. With the switch in the LFO 1
position (upwards), you choose the first Low Frequency Oscillator LFO 1 as the control source; with the
switch in the LFO 2 (downward) position, the second Low Frequency Oscillator LFO 2 is chosen as the
control source.
4.4.1.5. LFO 1 / LFO 2
Allows the choice of the Low Frequency Oscillator - LFO 1 or 2 as the modulation source applied to the
FREQUENCY of the filter.
4.4.1.6. EG AMT
Governs the amount of ADSR Envelope Generator applied to the Cutoff FREQUENCY. In this way, it is
possible to change the effectiveness in the articulation of sound. If EG AMT is at maximum and Cutoff
FREQUENCY is also at maximum, the filter - simply - does not close.
4.4.2. 18 dB VCF - Audio and Control Connections
Below, the description of the control and audio connections related to the 18 dB VCF filter on the front
panel of the synthesizer.
4.4.2.1. CV IN FLT
It receives the possible external control source applied to the Cutoff FREQUENCY. The control signal,
unprocessed, must be attenuated at the source.
4.4.2.2. VCF OUT
Is the audio output of the 18 dB VCF module. In this way, it is possible to use Grp A1 as a sophisticated
processor for static or dynamic audio processing through modulation.
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14

Grp A1 - Owner’s Manual
4.5. ENVELOPE GENERATOR
The Envelope Generator produces the transient control signal necessary for the articulation of the filtering
over time. Its signal can also be used (but not only) to control the level of the VCA Amplifier.
La grafica riproduce, per comodità,
anche i comandi relativi al Filtro 18dB
VCF.
4.5.1. ENVELOPE GENERATOR
-
Panel Controls
Below is a description of the panel
commands available for the ADSR
Envelope Generator.
4.5.1.1. ATTACK
Adjusts the Attack time required to go from the minimum value to the maximum control value. Depending
on the FAST, MID or SLOW position of the panel switch, the attack time varies between 0 and 1 second, 2.5
seconds or 8 seconds.
4.5.1.2. DECAY
Adjusts the Decay time required to go from the maximum value reached at the end of ATTACK to the
Sustain level. If the value of Sustain is at its maximum, the Decay has no effect. The duration is between 0
and 3 seconds, or 15 seconds or 40 seconds depending on the FAST, MID or SLOW position of the panel
switch.
4.5.1.3. SUSTAIN
Adjusts the level of Sustain that is extended until the Gate Off.
4.5.1.4. RELEASE
Adjusts the Release time required to move from the Sustain level (if nonzero) to the minimum level
corresponding to the end of the Envelope trajectory. The duration is between 0 and 3 seconds, or 15
seconds, or 40 seconds, depending on the FAST, MID, or SLOW position of the panel switch.
4.5.1.5. MID / FAST / SLOW
The times of Attack, Decay and Release are adjustable in three excursion fields through this switch. You can
choose between MID intermediate travel (top switch), FAST (middle position switch) or SLOW (low position
switch).
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Grp Synthesizer A1
®
1V/Oct IN GATE IN CV IN PWM CV IN FLT CV IN VCA EXT IN VCF OUT EG OUT LFO 2 OUT PHONES MAIN OUTVCO OUT
010 010
b #
010 010
010 010 010
010 010 010 010 010
010 010 010 010
010
010
010
MIDI INTERFACE VCO
MIDI TO CV KEY VEL FEG
GLIDE BEND AMT
8'
4'
16' SAW
SQR
TRI
LFO 1
LFO 2
EG
MAN
LFO 1
TUNE
PWM FM AMT
HOLD
FILTER EG
GATE + REL
MAIN OUT
VCA
NOISE LEVELVCO LEVEL SUB LEVEL
OCTAVE WAVE
DISABLE
ACT
FMTRKRESONANCEFREQUENCY DIST
LFO 1
LFO 2
18 dB VCF
DECAY RELEASESUSTAINATTACK EG AMT
SLOW
RATE
MID
RATE
FAST
SHAPE
RND
SLOW
MID
FAST
SHAPE
LFO 1-S&H
LFO 2
ENVELOPE GENERATOR
MID
SLOW
FAST
010
LFO 1 OUT

Grp A1 - Owner’s Manual
4.5.2. ENVELOPE GENERATOR - Control Connections
Below, the description of the control connections of the ADSR Envelope Generator present on the
synthesizer control panel.
4.5.2.1. GATE IN
The connection accepts the analog voltage 0/+5V necessary to trigger the Envelope Generator.
4.5.2.2. EG OUT
The connection provides the control signal processed by the ADSR Envelope Generator.
The voltage is 0/+5V.
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Grp A1 - Owner’s Manual
4.6. VCA - Voltage Controlled Amplifier
The Voltage Controlled Amplifier allows you to control the volume of the signal produced by the A1
synthesizer over time. You can choose three different control sources with the FILTER EG / HOLD / GATE +
REL switch; moreover, it is possible to control the level of the Amplifier from the outside through voltage
connected to the CVI input in VCA.
4.6.1. VCA - Panel Controls
Below, the description of the panel commands that govern the operation of the
VCA.
4.6.1.1. GATE+ REL / HOLD / FILTER EG
Allows you to choose between three possible control sources inside the A1 synthesizer.
• With the switch in the FILTER EG position, the Amplifier is controlled by the ADSR Envelope
Generator which also opens the VCF.
• With the switch in the HOLD position, the Amplifier is always open and the sound - compatible
with the other settings of VCO, MIXER and VCF - never ends.
• With the switch in the GATE + REL position, the Amplifier opens with the Gate On, remains at the
maximum level as long as the Gate voltage persists and, at the Gate Off, uses the Release time
programmed in the ADSR Filter Envelope as long as this makes functional sense.
4.6.1.2. MAIN OUT
Adjust the output volume of the instrument.
4.6.2. VCA - Connessioni di controllo e audio
Below is the description of the control and audio connections on the A1 synthesizer panel.
4.6.2.1. CV IN VCA
Input for the control signal applied to the level of the Voltage Controlled Amplifier. A voltage of 0V closes
the Amplifier; the maximum receivable voltage is +5V.
To control the VCA only with an external CV voltage, it is necessary not to activate the Gate (indifferently,
analog or MIDI) and the Filter Envelope. With the VCA only under external voltage, it is recommended to
limit the controls to only 1V/Oct management for the pitch of the oscillator, without using MIDI.
4.6.2.2. MAIN OUT
Is the audio output of the synthesizer.
4.6.2.3. PHONES
Is the output for listening to headphones, its volume is always regulated by the MAIN OUT command.
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Grp Synthesizer A1
®
1V/Oct IN GATE IN CV IN PWM CV IN FLT CV IN VCA EXT IN VCF OUT EG OUT LFO 2 OUT PHONES MAIN OUTVCO OUT
010 010
b #
010 010
010 010 010
010 010 010 010 010
010 010 010 010
010
010
010
MIDI INTERFACE VCO
MIDI TO CV KEY VEL FEG
GLIDE BEND AMT
8'
4'
16' SAW
SQR
TRI
LFO 1
LFO 2
EG
MAN
LFO 1
TUNE
PWM FM AMT
HOLD
FILTER EG
GATE + REL
MAIN OUT
VCA
NOISE LEVELVCO LEVEL SUB LEVEL
OCTAVE WAVE
DISABLE
ACT
FMTRKRESONANCEFREQUENCY DIST
LFO 1
LFO 2
18 dB VCF
DECAY RELEASESUSTAINATTACK EG AMT
SLOW
RATE
MID
RATE
FAST
SHAPE
RND
SLOW
MID
FAST
SHAPE
LFO 1-S&H
LFO 2
ENVELOPE GENERATOR
MID
SLOW
FAST
010
LFO 1 OUT

Grp A1 - Owner’s Manual
4.7. LFO 1 - S&H
The module includes a cyclic modulation source LFO 1 - Low Frequency Oscillator and a Sample & Hold,
which produces random control voltages. As in higher-end GRP instruments, it is possible to adjust the
symmetry of triangular and square waves obtaining ramp - triangular - sawtooth and impulsive - square -
impulsive behaviors.
Signal LED makes the selected frequency visible.
4.7.1. LFO 1 - S&H - Panel Controls
Below is a description of the form's panel controls..
4.7.1.1. RATE
Adjust modulation speed. Depending on the position of the adjacent switch, you can work in the three
excursions MID (top switch), FAST (middle switch) or SLOW (bottom switch). The speed varies from 0.1 Hz
to 3 Hz (SLOW), from 3 Hz to 100 Hz (MID) or from 85 Hz to 2400 Hz (FAST).
It is advisable not to underestimate the modulations in audio band obtainable by placing the speed of the
LFO circuit on FAST.
4.7.1.2. MID / FAST / SLOW
It is the switch that allows you to choose the three speed excursions previously indicated.
4.7.1.3. SHAPE
Regola the symmetry of the selected waveform with the three-position switch TRIANGLE / RND / PULSE
(see below). Depending on the choice made with the switch, you can get the sawtooth variation - triangular
- ramp (top position), or you can get the pulse variations 5% - square - pulse 95% (bottom switch).
The central position of the switch activates the Sample & Hold behavior in stepped mode.
4.7.1.4. TRIANGLE / RND / PULSE
Activates the desired behavior for the circuit. In the upper position, you can achieve sawtooth variations -
symmetrical triangular - ascending ramp; in the central position (RND), the module functions as Stepped
Sample And Hold; In the lower position, you can get the impulsive variations 1% - square to 50% - impulsive
to 99%.
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Grp Synthesizer A1
®
1V/Oct IN GATE IN CV IN PWM CV IN FLT CV IN VCA EXT IN VCF OUT EG OUT LFO 2 OUT PHONES MAIN OUTVCO OUT
010 010
b #
010 010
010 010 010
010 010 010 010 010
010 010 010 010
010
010
010
MIDI INTERFACE VCO
MIDI TO CV KEY VEL FEG
GLIDE BEND AMT
8'
4'
16' SAW
SQR
TRI
LFO 1
LFO 2
EG
MAN
LFO 1
TUNE
PWM FM AMT
HOLD
FILTER EG
GATE + REL
MAIN OUT
VCA
NOISE LEVELVCO LEVEL SUB LEVEL
OCTAVE WAVE
DISABLE
ACT
FMTRKRESONANCEFREQUENCY DIST
LFO 1
LFO 2
18 dB VCF
DECAY RELEASESUSTAINATTACK EG AMT
SLOW
RATE
MID
RATE
FAST
SHAPE
RND
SLOW
MID
FAST
SHAPE
LFO 1-S&H
LFO 2
ENVELOPE GENERATOR
MID
SLOW
FAST
010
LFO 1 OUT

Grp A1 - Owner’s Manual
4.7.2. LFO 1 - S&H - Control Connections
Di seguito, la descrizione delle connessioni di controllo relative al modulo LFO 1 - S&H presenti sul pannello
comandi dello strumento.
4.7.2.1. LFO 1 OUT
Below is a description of the control connections related to the LFO 1 - S&H module on the instrument
control panel.
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Grp A1 - Owner’s Manual
4.8. LFO 2
The module produces a cyclic control voltage adjustable between triangular and pulse with different SHAPE
symmetry values. Also in this case, the signal LED makes the selected frequency visible.
4.8.1. LFO 2 - Controlli di pannello.
Below is a description of the LFO 2 commands on the front panel.
4.8.1.1. RATE
Adjust modulation speed; Depending on the position of the adjacent switch, you can work in the three
excursions MID (top switch), FAST (middle switch) or SLOW (bottom switch). The speed varies from 0.1 Hz
to 3 Hz (SLOW), from 3 Hz to 100 Hz (MID) or from 85 Hz to 2400 Hz (FAST).
It is advisable not to underestimate the modulations in audio band obtainable by placing the speed of the
LFO circuit on FAST.
4.8.1.2. MID / SLOW / FAST
Is the switch that allows you to choose the three speed excursions previously indicated.
4.8.1.3. SHAPE
Adjust the symmetry of the selected waveform with the two-position switch TRIANGLE / PULSE (see below).
Depending on the choice made with the switch, it is possible to obtain the sawtooth variation - triangular -
ramp (top position), or it is possible to obtain the pulse variations 5% - square - pulse 95% (bottom switch).
4.8.1.4. TRIANGLE / PULSE
Activates the desired behavior for the circuit. In the upper position, you can achieve sawtooth variations -
symmetrical triangular - ascending ramp; In the lower position, you can get the impulsive variations 1% -
square to 50% - impulsive to 99%.
4.8.2. LFO 2 - Connessioni di controllo
Below is a description of the control connections related to LFO 2 on the command panel.
4.8.2.1. LFO 2 OUT
The port provides the modulation signal produced by the Low Frequency Oscillator - LFO 2.
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Grp Synthesizer A1
®
1V/Oct IN GATE IN CV IN PWM CV IN FLT CV IN VCA EXT IN VCF OUT EG OUT LFO 2 OUT PHONES MAIN OUTVCO OUT
010 010
b #
010 010
010 010 010
010 010 010 010 010
010 010 010 010
010
010
010
MIDI INTERFACE VCO
MIDI TO CV KEY VEL FEG
GLIDE BEND AMT
8'
4'
16' SAW
SQR
TRI
LFO 1
LFO 2
EG
MAN
LFO 1
TUNE
PWM FM AMT
HOLD
FILTER EG
GATE + REL
MAIN OUT
VCA
NOISE LEVELVCO LEVEL SUB LEVEL
OCTAVE WAVE
DISABLE
ACT
FMTRKRESONANCEFREQUENCY DIST
LFO 1
LFO 2
18 dB VCF
DECAY RELEASESUSTAINATTACK EG AMT
SLOW
RATE
MID
RATE
FAST
SHAPE
RND
SLOW
MID
FAST
SHAPE
LFO 1-S&H
LFO 2
ENVELOPE GENERATOR
MID
SLOW
FAST
010
LFO 1 OUT