GRP Synthesizer A8 User manual

Grp Synthesizer
A8 USER’S MANUAL
www.grpsynthesizer.it

Grp Synthesizer A8 User’s Manual V. 2.06 2

Grp Synthesizer A8 User’s Manual V. 2.06 3
CONTENTS
CONTENTS 3
FOREWORD 6
SOME WORDS OF WISDOM 6
Operating Conditions 6
Power Supply 6
Operation 6
Maintenance 6
Proper Use
SETUP AND CONNECTIONS 7
Contents 7
Connections 7
AC Connections 7
MIDI Connections 7
Audio Connections 7
Rear Panel Audio Connections 7
Front Panel Audio Connections 8
Analog CV/Gate Connections 8
OVERVIEW 9
WHAT IS INSIDE THE A8? 10
BASIC OPERATIONS 11
Powering the instrument 11
Tuning the instrument 11
Dealing with Modes and MIDI Interface 11
Note Priority 11
Mode Selection 12
Pitch Bend 12
MIDI Interface 12
CV Offset 13
FRONT PANEL CONNECTIONS 15
CV-Gate-Trigger 15
Sequencer 15
Filter 16
Main Out 16
REAR PANEL CONNECTIONS 17
Power 17
MIDI 17
Audio 17
Future Upgrades 17
A8 AUDIO AND MODULATION ROUTINGS 18
SOUND SOURCES AND SOUND MODIFIERS PATH 18
VOLTAGE CONTROLLED OSCILLATOR 1-6 19
Frequency Control 19

Grp Synthesizer A8 User’s Manual V. 2.06 4
Waveform Control 20
The waveform 20
Output 21
VOLTAGE CONTROLLED OSCILLATOR 1-6 REFERENCE 22
RING MODULATOR 23
NOISE GENERATOR 23
NOISE GENERATOR REFERENCE 23
VOLTAGE CONTROLLED FILTER 1-2 24
VOLTAGE CONTROLLED FILTER 1-2 REFERENCE 25
Controls in common for both Filters 25
Controls for 24 dB/Oct transistor-ladder Low Pass Filter 25
Controls for 12 dB/Oct state-variable Filter 26
FIXED FILTER BANK 26
FIXED FILTER REFERENCE 26
VOLTAGE CONTROLLED AMPLIFIER 27
VOLTAGE CONTR AMPLIFIER REFERENCE 27
MAIN MIX / AUTO PAN 28
MAIN MIX / AUTO PAN REFERENCE 28
Controls for the Upper Section 28
Controls for the Lower Section 28
Controls for the Auto Pan Section 29
STEREO MAIN 29
A8 MODULATION SOURCES AND CONTROL MODIFIERS 30
Modulation Sources 31
Modulation Destinations
VOLTAGE CONTROLLED LOW FREQUENCY OSCILLATOR 1-2 33
Frequency Control 33
Waveform Control 33
Hard Sync 34
Output Offset 34
Shaping 34
VOLTAGE CONTROLLED LOW FREQUENCY OSCILLATOR 1-2 REFERENCE 35
Frequency Controls 35
Waveform Controls 35
Sync Controls 35
Shaping Controls 36
LOW FREQUENCY OSCILLATOR 3 36
Frequency and Frequency Range 36
Waveshape 36
Output Control 37
Modulation Routings 37
LOW FREQUENCY OSCILLATOR 3 REFERENCE 37
Frequency 37
Waveshape Controls 37
Output Controls 37
Destination Controls 37
ENVELOPE GENERATORS 38
Common behaviours and controls - Trigger Mode 38

Grp Synthesizer A8 User’s Manual V. 2.06 5
Common behaviours and controls - Gate source select 39
Common behaviours - Envelope Structure 39
SIX STAGE ENVELOPE GENERATOR (ENV 1 / ENV 4) 39
SIX STAGE ENVELOPE GENERATOR (ENV 1 / ENV 4) REFERENCE 40
Envelope stages parameters 40
Gate (source) parameters 40
Trig switch parameters 40
Activity LED 41
SIX STAGE ENVELOPE GENERATOR (ENV 3 / ENV 6) 41
SIX STAGE ENVELOPE GENERATOR (ENV 3 / ENV 6) REFERENCE 41
FOUR STAGE ENVELOPE GENERATOR (ENV 2 / ENV 5) 42
FOUR STAGE ENVELOPE GENERATOR (ENV 2 / ENV 5) REFERENCE 42
Envelope stages parameters 42
Gate (source) parameters 42
Trig switch parameters 42
Activity LED 43
FOUR STAGE AUXILIARY ENVELOPE GENERATOR (ENV 7) 43
FOUR STAGE AUXILIARY ENVELOPE GENERATOR (ENV 7) REFERENCE 43
Envelope stage parameters 43
Gate (source) parameters 43
Trig switch parameters 44
Activity LED 44
Assign Switch 44
SAMPLE & HOLD / NOISE GENERATOR 44
Input Source Selection 45
Clock Source Selection 45
Glide 45
Clocked Envelope 45
SAMPLE & HOLD / NOISE GENERATOR REFERENCE 45
Sample & Hold Controls 45
Noise Generator Controls 46
STEP SEQUENCER 47
Clock and Divider/Multiplier Parameters 47
Advance and Repetitions Parameters 47
Sequencer Mode Parameters 47
Column Parameters 48
Step Parameters 48
Assign Parameters 48
STEP SEQUENCER REFERENCE 49
Integration, Quantization, Range and Assign Section 49
VCO Sequencer Enable 49
PW SEQ ENA(ble) 50
F(i)LT(er) SEQ ENA(ble) 50
Column A Section - Column B Section 51
Clock & Clock Divider 51
Step Repeat & Loop 52
Sequencer mode 52
Manual controls 53
Sequencer remote connections and controls on the front panel 53

Grp Synthesizer A8 User’s Manual V. 2.06 6
FOREWORD
Thank you for purchasing the Grp Synthesizer A8: this machine will rewards you with years of sonic
satisfactions and, to ensure your instrument will functions properly, please read this manual.
SOME WORDS OF WISDOM
Read the following safely tips carefully! You should always observe some basic precautions when
dealing with electronic equipment, for you safety and for safety of your own equipment.
Operating Conditions
•Never use the synthesizer under potentially damp/wet conditions such bathrooms, swimming
pools, etc.
•Do not use the instrument in extremely dusty and dirty environments.
•Do not place the instrument near heat sources like radiators.
•Do not expose the instrument to direct sunlight; the wooden cabinet is varnished with a
traditional and trusted procedure, but ultraviolet rays from sunlight can quickly fade the
original wooden colour.
•Do not expose the device to extreme vibrations.
•Save the original crate and boxing for future shipping of the instrument.
Power Supply
•Always check that the AC current in your area is correct for the instrument BEFORE turning it
on. The Grp Synthesizer A8 can be powered with 110-220 V 50-60 Hz, switchable in the rear
panel. Please, check and re-check.
•Unplug the device when you are not using it for longer periods.
•Never touch the plug with wet hands.
•When unplugging the instrument, always grab and pull the plug, never the cable.
Operation
•Although you are a rockstar, NEVER place cans of beer, coke, water (?) or other potentially
spilling liquids on or near the instrument.
•The Grp A8 Synthesizer is an heavy synthesizer: place it on a suitable solid surface or table.
•The Grp A8 Synthesizer can be very LOUD: please, be careful with the big volume knob on
the lower right of the front panel.
Maintenance
•Do not open the instrument; do not unscrew the front/rear panels. Inside the instrument,
there aren’t user’s serviciable parts.
Proper Use
•This synthesizer is designed exclusively to produce audio rate frequency signals for musical
purpose. Any other use is prohibited and voids the warranty extended by Grp Synthesizer.
Grp Synthesizer is non liable for damanges due to incorrect use.

Grp Synthesizer A8 User’s Manual V. 2.06 7
SETUP AND CONNECTIONS
Contents
Your Grp Synthesizer A8 comes completed with:
•The instrument (pretty big, eh?) itself.
•The suitable power supply cable.
•This manual.
Ensure that all the items above listed were included. If something is missing, contact your local dealer.
As said above, we recommend that you carefully save the original packing material for future
transport/shipping.
Connections
In order to get started with your Grp Synthesizer A8, you will need some connections:
•Suitable AC powering. Make sure (twice) that the power available in your country matches
the correct position in voltage switch 110-220V on the rear panel.
•A MIDI Keyboard/Controller with proper MIDI cable. Those can be unnecessary if you plan to
use the synthesizer only with analog CV/Gate or with the internal Step Sequencer.
•A analog CV/Gate source, with a bunch of !” TS unbalanced cables.
AC Connections
Without doubts, the only place to make
connection for AC cord is on the rear panel;
please. DO NOT detach the ground
connection.
MIDI Connections
Another easy issue:
the MIDI Port (with In and Thru) is located on the rear panel. While the Grp
Synthesizer A8 doesn’t emit any MIDI signal, it can receive MIDI messages
simoultaneously from up to two different sources connected to its MIDI Input.
The data received at Input connector are echoed back to MIDI Thru
connector.
Audio Connections
The things are more varied: you can choose
different connections, suited to different
needs, on both front and rear panel.
Rear Panel Audio Connections
If you’ll use the A8 in a fixed, studio
environment, is best to use the Rear panel
Audio Connections, otherwise, you’ll be free to use the more easy access to the front panel
connection (more on this, later). On the rear, you’ll find:

Grp Synthesizer A8 User’s Manual V. 2.06 8
•SECTION OUT UPPER LEFT-RIGHT: separate stereo out for Upper part after Pan/AutoPan
module, but before the Main Out Volume.
•SECTION OUT LOWER LEFT-RIGHT: separate stereo out for the Lower part after
Pan/AutoPan module, but before the Main Out Volume.
•MAIN OUT LEFT-RIGHT LOW LEVEL: doubles the front panel main stereo output (this
output is at a quiet low level).
•MAIN OUT LEFT-RIGHT HIGH LEVEL: doubles the front panel main stereo output (be
careful: this output is at a fairly high level).
•LEFT+RIGHT MONO OUT: the sum of Upper and Lower Sections; the connection doubles
the front panel mono output.
Front Panel Audio Connections
On the front panel, there are the following audio connections:
•MONO OUT: summed signal of Upper and Lower Sections (same
as Mono Out on the rear panel)
•PHONES: headphones stereo output.
•LEFT - RIGHT LOW LEVEL OUT: low impedance stereo output.
•LEFT - RIGHT HIGH LEVEL OUT: (fairly) high impedance stereo
output.
Analog CV/Gate Connections
If you dislike (or if you dont need) MIDI, you can rely on old school analog CV and Gate connections;
on the front panel you’ll find direct access to separate Upper and Lower Sections of the instrument
or, for a full scale control on a single couple of CV/Gate, the common Lower-Upper analog interface.
In details, there are connections for:
•LOWER SECTION Connections: Trig Input (0/+5V), Gate Input (0/+5V), CV Input (1V/Oct).
•UPPER SECTION Connections: as above.
•LOWER and UPPER Connections: as above, in common for both sections.

Grp Synthesizer A8 User’s Manual V. 2.06 9
OVERVIEW
The Grp Synthesizer A8 is a complex, but not-so complex analog machine dual structure/bitimbral,
with an integrated Step Sequencer.
Each part (Upper or Lower section) is a complete and independent analog synthesizer fitted with
three VCOs each with separate SubOsc, one Ring Modulator, one Audio Mixer, two dynamic VCFs,
one Fixed Filter Bank, one VCA, three EGs, one LFO.
The above picture shows the modules concerning the Upper and Lower sections. As you can see,
they are disposed in a pretty simmetrical way on the front panel.
In addition, there is a group of common modules who can be shared by the two section or can
controls both sections simoultaneously; they are: Tuning-Portamento, MIDI Interface, Sample &
Hold/Noise Generator, Auxiliary Envelope Generator 7, Main Mix/Auto Pan, LFO 3, Main Volume,
Step Sequencer and Front Panel Connections.
The above picture shows the modules in common for both Upper and Lower sections of the
instrument.

Grp Synthesizer A8 User’s Manual V. 2.06 10
WHAT’S INSIDE THE A8?
The whole instrument contains several different circuits:
•A MIDI INTERFACE who converts MIDI data in CV, Gate, Trigger, Key Velocity and Clock
data for Upper and Lower Sections.
•An ANALOG PORT who receives CV, Gate, Trigger, Clock for Upper and Lower Sections.
•A STEP SEQUENCER who drives VCO Freq & PWM, VCF Freq, EG Gate for Upper and
Lower Sections.
•A dual section ANALOG SYNTHESIZER able to create two entirely separate patches, or - at
request - work in cross audio rate modulation between VCOs on VCOs and VCOs on VCFs.
The above (simplified) picture shows the interactions between the different components of the A8.
Feel free to experiment with different sections of the synthesizer; first, with Upper/Lower synth parts,
then, with Step Sequencer.