SYNTAX CVGT1 Analog Interfaces Modular User Manual
- June 4, 2024
- SYNTAX
Table of Contents
CVGT1 User Manual
Copyright © 2021 (Syntax) PostModular Limited. All rights reserved. (Rev 1 July 2021)
Introduction
Thank you for purchasing the SYNTAX CVGT1 Module. This manual explains what
the CVGT1 Module is and how it works. This module has exactly the same
specification as the original Synovatron CVGT1.
The CVGT1 Module is an 8HP (40mm) wide Eurorack analog synthesizer module and
is compatible with the Doepfer™ A-100 modular synthesizer bus standard.
CVGT1 (Control Voltage Gate Trigger module 1) is a CV and Gate/Trigger
interface primarily aimed at providing a means of exchanging CV and timing
pulse control signals between Eurorack synthesizer modules and Buchla™ 200e
Series although it will also work with other banana socketed synths such as
Serge™ and Bugbrand™.
Caution
Please ensure you use the CVGT1 Module in accordance with these instructions
especially taking great care to connect the ribbon cable to the module and the
power bus correctly. Always double-check!
Only fit and remove modules with the rack power off and disconnected from the
mains electricity supply for your own safety.
Refer to the connection section for ribbon cable connection instructions.
PostModular Limited (SYNTAX) cannot be held responsible for any damage or harm
caused through incorrect or unsafe use of this module. If in doubt, stop and
check.
CVGT1 Description
The CVGT1 Module has four channels, two for CV signal translation and two for
timing signal translation as follows:-
Banana to Euro CV Translation – Black Channel
This is a precision DC coupled buffered attenuator designed to translate input
signals in the range of 0V to +10V to output compatible with the ±10V bipolar
range of Eurorack synthesizers.
cv in A 4mm banana socket input with a range of 0V to +10V (Buchla™
compatible).
cv out A 3.5mm jack socket output (Eurorack compatible).
scale This switch allows the gain to be changed to match the scale factor of
the cv in input signal. This can be set to deal with 1V/octave, 1.2V/octave
and 2V/octave input scales; in the 1 position, the amplifier has a gain of 1
(unity), in the 1.2 position it has a gain of 1/1.2 (attenuation of 0.833) and
in the 2 position it has a gain of 1/2 (attenuation of 0.5).
offset This switch adds an offset voltage to the input signal if
required. In the (0) position the offset is unchanged; a positive going input
signal (e.g. envelope) will result in a positive going output signal; In the
(‒) position -5V is added to the input signal which can be used to shift a
positive going input signal down by 5V. The offset level will be affected by
the scale switch setting.
The simplified schematics (a) to (f) explain in simple arithmetic terms how an
input signal in the range of 0V to +10V is translated using the various offset
and scale switch positions. Schematics (a) to (c) show the offset switch in
the 0 positions for each of the three scale positions. Schematics (d) to (f)
show the offset switch in the ‒ position for each of the three scale
positions.
Note that when the scale switch is in the 1 position and the offset switch is
in the 0 position, as shown in schematic (a), the signal is not changed. This
is useful for interfacing banana connector synthesizers that have 1V/octave
scaling e.g. Bugbrand™ to Eurorack synthesizers.
Euro to Banana CV Translation – Blue Channel
This is a precision DC coupled amplifier designed to translate bipolar input
signals from Eurorack synthesizers into a 0V to +10V range.
cv in A 3.5mm jack socket input from a Eurorack synthesizer
cv out A 4mm banana socket output with an output range of 0V to +10V
(Buchla™ compatible).
scale This switch allows the gain to be changed to match the scale factor
of the synthesizer connected to cv out. This can be set for 1V/octave,
1.2V/octave and 2V/octave scales; in the 1 position the amplifier has a gain
of 1 (unity), in the 1.2 position it has a gain of 1.2, and in the 2 positions
it has a gain of 2.
offset This switch adds an offset to the output signal. In the 0 position, the
offset is unchanged; a positive going input signal (e.g. envelope) will result
in a positive going output. In the (+) position 5V is added to the output
signal which can be used to shift a negative-going input signal up by 5V. The
offset level will be unaffected by the scale switch setting.
–CV LED indicator lights if the output signal goes negative to warn that the
signal is outside the useful range of a 0V to +10V range synthesizer.
gnd A 4mm banana ground socket. This is used to provide a ground reference
(signal return path) to another synthesizer if required. Just connect this to
the banana socket ground (usually on the back) of the synth you want to use
the CVGT1 with.
The simplified schematics (a) to (f) explain in simple arithmetic terms what
input ranges are required to translate to an output range of 0V to +10V using
the various offset and scale switch positions. Schematics (a) to (c) show the
offset switch in the 0 position for each of the three scale positions.
Schematics (d) to (f) show the offset switch in the + position for each of the
three scale positions.
Note
that when the scale switch is in the 1 position and the offset switch is in
the 0 positions, as shown in schematic (a), the signal is not changed. This is
useful for interfacing Eurorack synthesizers to banana connector synthesizers
that have 1V/octave scaling e.g. Bugbrand™.
Banana to Euro Gate Trigger Translator – Orange Channel
This is a timing signal converter designed specifically to convert the tri-
state timing pulse output from Buchla™ 225e and 222e synthesizer modules into
Eurorack compatible gate and trigger signals. It will work with any signal
that exceeds the input thresholds of either the gate or trigger detectors as
follows. pulse in A 4mm banana socket input compatible with Buchla™ pulse
outputs in the range of 0V to +15V.
gate out A 3.5mm jack socket Eurorack gate output. The output goes high
(+10V) when the pulse in voltage is above +3.4V. This is used to follow the
gate or sustain part of Buchla™ 225e and 222e module pulses although any
signal exceeding +3.4V will cause this output to go high.
Refer to the example timing diagram below. The LED illuminates when gate out
is high.
trig out A 3.5mm jack socket Eurorack trigger output. The output goes
high (+10V) when the pulse in voltage is above +7.5V. This is used to follow
the initial trigger part of
Buchla™ 225e and 222e module pulses although any signal exceeding +7.5V will
cause this output to go high.
Note that trig out does not shorten pulses it just transmits the high-level
pulses at the width presented to pulse in which are all narrow pulses on
Buchla™ synth pulse outputs. Refer to the example timing diagram on the next
page.
The
timing diagram above shows four example pulses in input waveforms and the gate
out and trig out responses. The input switching thresholds for the gate and
trigger level detectors are shown at +3.4V and +7.5V. The first example (a)
shows the pulse shape similar to that of a Buchla™ 225e and 222e module
pulses; an initial trigger pulse followed by a sustained level which is
reflected in the gate out and trig out responses. The other examples show
that pulses are just passed through (at +10V) to gate out and trig out if they
exceed respective thresholds. A signal that exceeds both thresholds will be
present on both outputs.
Euro to Banana Gate Trigger Translator – Red Channel
This is a timing signal converter designed to convert Eurorack gate and
trigger signals into a timing pulse output compatible with a Buchla™
synthesizer modules pulse inputs.
trig in A 3.5mm jack socket trigger input from a Eurorack synthesizer.
This can be any signal that exceeds the input threshold of +3.4V. It will
generate a +10V narrow pulse (trimmer adjustable in the range 0.5ms to 5ms;
factory set to 1ms) at pulse out irrespective of the input pulse width.
gate in A 3.5mm jack socket gate input from a Eurorack synthesizer. This can
be any signal that exceeds the input threshold of +3.4V. This input is
specifically designed to create an output at pulse out that is compatible with
Buchla™ 225e and 222e module pulses i.e. it will cause a tri-state output
pulse. The gate in leading edge will generate a +10V narrow trigger pulse
(also trimmer adjustable in the range 0.5ms to 5ms; factory set to 4ms) at
pulse out irrespective of the input
pulse width. It will also generate a +5V sustaining ‘gate’ signal for the
duration of the input pulse if it extends beyond the narrow trigger pulse.
This can be seen in example (a) in the timing diagram on the next page.
pulse out A 4mm banana socket output compatible with Buchla™ synthesizer
pulse inputs. It outputs a composite (an OR function) of the signals derived
from the trig in and gate in pulse generators. The output has a diode in its
path so it can simply be connected to other Buchla™ compatible pulses without
signal contention. The LED illuminates when pulse out is high.
The timing diagram above shows four examples of gate in and trig in input
waveforms and the pulse out responses. The input switching thresholds for the
gate and trigger level detectors are shown at +3.4V.
The first example (a) shows how a Buchla™ 225e and 222e module compatible
pulse is generated in response to a gate in signal; an initial 4ms trigger
pulse followed by a sustain level lasting the length of the gate in signal.
Example (b) shows what happens when the gate in signal is short and just
generates the initial 4ms trigger pulse without a sustaining level.
Example (c) shows what happens when the trig in signal is applied; the output
is a 1ms trigger pulse triggered off the leading edge of the trig in signal
and ignores the remainder of the trig in signal duration. Example (d) shows
what happens when a combination of gate in and trig in signals are present.
Connection Instructions
Ribbon Cable
The ribbon cable connection to the module (10-way) should always have the red
stripe at the bottom to line up with the RED STRIPE marking on the CVGT1
Board. The same for the other end of the ribbon cable that connects to the
modular synth rack’s power connector (16-way). The red stripe must always go
to the pin 1 or -12V position. Note that Gate, CV and +5V pins are not used.
The +12V and -12V connections are diode protected on the CVGT1 module to
prevent damage if reverse connected.
Adjustments
These adjustments should only be performed by a suitably qualified person.
CV scale and offset adjustments
The offset voltage reference and scale adjustment pots are on the CV1 board.
These adjustments should be performed with the aid of an adjustable DC voltage
source and a precision Digital Multi-Meter (DMM), with a basic accuracy of
better than ±0.1%, and small screwdriver or trim tool.
-
Set the front panel switches as follows:-
Black socket channel: scale to 1.2
Black socket channel: offset to 0
Blue socket channel: scale to 1.2
Blue socket channel: offset to 0 -
Black socket channel: Measure cv out with a DMM and with no input applied to cv in – record the value of the residual offset voltage reading.
-
Black socket channel: Apply 6.000V to cv in – this should be checked with the DMM.
-
Black socket channel: Measure cv out with a DMM and adjust RV3 for a reading of 5.000V above the value recorded in step 2.
-
Black socket channel: Set offset to ‒.
-
Black socket channel: Measure cv out with a DMM and adjust RV1 for 833mV above the value recorded in step 2.
-
Blue socket channel: Measure cv out with a DMM and with no input applied to cv in – record the value of the residual offset voltage reading.
-
Blue socket channel: Apply 8.333V to cv in – this should be checked with the DMM.
-
Blue socket channel: Measure cv out with a DMM and adjust RV2 for10.000V above the value recorded in step 7
Note there is only one scale control for the black socket channel and one for the blue socket channel so the adjustments are optimized for a scale of 1.2. However, due to the use of high precision components used the other scale positions will track the 1.2 set to within 0.1%. Similarly, the offset reference voltage adjustment is shared between both channels.
Pulse timing adjustments
The pulse timing adjustment pots are on the GT1 board. The adjustments should
be performed with the aid of a clock or repeating gate source, an oscilloscope
and a small screwdriver or trim tool.
The widths of the pulses produced at pulse out from gate in and trig in are
factory set to a gate in leading pulse width of 4ms (RV1) and trig in pulse
width of 1ms (RV2). These can however be set anywhere from 0.5ms to over 5ms.
CVGT1 Specification
Banana to Euro CV – Black Channel
Input: 4mm banana socket cv in
Input range: ±10V
Input impedance: 1MΩ
Bandwidth: DC-19kHz (-3db)
Gain: 1.000 (1), 0.833 (1.2), 0.500 (2) ±0.1% max
Output: 3.5mm jack cv out
Output range: ±10V
Output impedance: <1Ω| Euro to Banana CV – Blue Channel
Input: 3.5mm jack cv in
Input range: ±10V
Input impedance: 1MΩ
Bandwidth: DC-19kHz (-3db)
Gain: 1.000 (1), 1.200 (1.2), 2.000 (2) ±0.1% max
Output: 4mm banana socket cv out
Output impedance: <1Ω
Output range: ±10V
Output indication: Red LED for negative outputs -cv
---|---
Banana to Euro Gate Trigger – Orange Channel
Input: 4mm banana socket pulse in
Input impedance: 82kΩ
Input threshold: +3.4V (gate), +7.5V (trigger)
Gate output: 3.5mm jack gate out
Gate output level: gate off 0V, gate on +10V
Trigger output: 3.5mm jack trig out
Trigger output level: trigger off 0V, trigger on +10V
Output indication: Red LED is on for duration of pulse in
Euro to Banana Gate Trigger – Red Channel
Gate input: 3.5mm jack gate in
Gate input impedance: 94kΩ
Gate input threshold: +3.4V
Trigger input: 3.5mm jack trig in
Trigger input impedance: 94kΩ
Trigger input threshold: +3.4V
Output: 4mm banana socket pulse out
Output level:
- Gate initiated: gate off 0V, gate on +10V initially (0.5ms to 5ms) falling to +5V for duration of gate in. Only the leading edge of the gate in signal initiates the timer. The pulse duration (0.5ms to 5ms) is set by a trimmer (factory set to 4ms).
- Trigger initiated: trigger off 0V, trigger on +10V (0.5ms to 5ms) initiatedby trig in. Only the leading edge of the trig in signal initiates the timer.The pulse duration (0.5ms to 5ms) is set by a trimmer.
- Pulse output: The gate and trigger initiated signals are OR’ed together using diodes. This allows other modules with diode-connected outputs to also be OR’d with this signal. Output indication: Red LED is on for the duration of pulse out
Please note that PostModular Limited reserves the right to change the
specification without notice.
General
Dimensions
3U x 8HP (128.5mm x 40.3mm); PCB depth 33mm, 46mm at ribbon connector
Power consumption
+12V @ 20mA max, -12V @ 10mA max, +5V is not used
A-100 Bus utilisation
±12V and 0V only; +5V, CV and Gate are not used
Contents
CVGT1 Module, 250mm 10 to 16-way ribbon cable, 2 sets of M3x8mm
Pozidrive screws, and nylon washers
Copyright © 2021 (Syntax) PostModular Limited. All rights reserved. (Rev 1
July 2021)
Environmental
All components used on the CVGT1 Module are RoHS compliant. To comply with the
WEEE Directive please do not discard into landfill – please recycle all Waste
Electrical and Electronic Equipment responsibly – please contact PostModular
Limited to return the CVGT1 Module for disposal if required.
Warranty
The CVGT1 Module is guaranteed against defective parts and workmanship for 12
months from the date of purchase. Note that any physical or electrical damage
due to misuse or incorrect connection invalidates the warranty.
Quality
The CVGT1 Module is a high quality professional analog device that was
lovingly and carefully designed, built, and tested in the United Kingdom by
PostModular Limited. Please be assured of my commitment to providing good
reliable and usable equipment! Any suggestions for improvements will be
gratefully received.
Contact details
Post Modular Limited
39 Penrose Street London
SE17 3DW
T: +44 (0) 20 7701 5894
M: +44 (0) 755 29 29340
E: sales@postmodular.co.uk
W: https://postmodular.co.uk/Syntax