Random*Source GTO SERGE User manual

SERGE
GTO
FOR EURORACK
IN
HOLDCYCLE
1V/OCT 1V/OCT
CYCLE
OUT OUT
VC RATERATE VC RATE RATE
GTO
IN
SERGE MODULAR
SYNC RUN
COUPLER
SMPL
INV
USER MANUAL
V1.0
RANDOM*SOURCE

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GTO
Installation ........................................................ 3
Overview ......................................................... 3
What’s new? What’s different? ......................................... 3
Serge GTO - Basic Operation.......................................... 4
Left side /// SMOOTH mode........................................... 4
Right side /// STEPPED mode (and more)................................. 4
1V/Oct Input (#8) ................................................... 8
Sync Input (#9) ..................................................... 8
GTO - First Steps ................................................... 9
Serge GTO - Patch Ideas ............................................ 10
DUAL GTO Patches ................................................ 12

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GTO
Installation
Always turn the eurorack case off and unplug the power cord before plugging or unplugging any eurorack power
cable. Do not touch any electrical terminals when attaching any eurorack power (bus board) cables.
The Serge GTO is an electronic music module requiring 50mA of +12VDC and 50 mA of -12VDC regulated
voltages and an appropriate power connector to operate. It must be properly installed into a eurorack format
modular synthesizer system case.
POWER YOUR CASE OFF before installing the module. Please use the power cable provided to connect the small
end of the power cable to the module: RED STRIPE to “-12V”, as indicated on the back of the module. Carefully
install and secure the module in your case. Power on, and ip the CYCLE switches to the DOWN position, SMPL
switche to the CENTER position. You should see an LED ashing for each channel. If either side seems constantly
ON or OFF, turn the RATE knob to the center position or slightly below to see each side cycling. Your module
should be ready to go now :-)
Please beware: Powering the module on anything more (or less) than +/-12V is not recommended and may
damage the module. Feeding any of the inputs (or outputs) with voltages outside a +/-12V range may damage the
module. This type of damage is not covered under warranty.
Overview
The Serge GTO is an evolution of the famous Serge Smooth & Stepped Generator. As its predecessor, it has two
sides, that are not identical, but differ in some aspects. The left side was traditionally the “Smooth Side” while the
right side was the “Stepped Side”. In the GTO, however, the right side can to some extent - in particular when the
SMPL switch (14) is in CENTER position - behave like a “smooth” side.
The GTO is a dual “lag and hold” device that can be quite a few things, depending on how you use it. It can be
patched as a slew, portamento, oscillator, LFO, metallizer, triggered staircase generator, subharmonic generator/
divider, VCA, lowpass-gate, sample and hold, track and hold, set of comparators, trigger delay, one-shot, envelope
follower, quadrature function generator, “bit-crusher” and much more.
What’s new? What’s different?
The Serge GTO is not just an improved SSG, but almost a complete redesign with the focus on stability, precision
and speed. Each side has a temperature-compensated 1V/Oct input for use as an oscillator with a frequency
range of up to 20kHz (left) and 8kHz (right). Each side tracks over 5 or 6 octaves. The right side offers 3 different
Sample modes plus a RUN input that vastly extend the track-and-hold possibilities of the classic SSG.

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Serge GTO
IN
HOLDCYCLE
1V/OCT 1V/OCT
CYCLE
OUT OUT
VC RATERATE VC RATE RATE
GTO
IN
SERGE MODULAR
SYNC RUN
COUPLER
SMPL
INV
3
LEFT OUT
1
INPUT
8
1V/OCT IN
5
RATE
4
HOLD IN 2
CYCLE OUT
11
COUPLER OUT
9
SYNC IN
10
CYCLE SW
6
CV IN
7
CV ATTEN.
1
INPUT
8
1V/OCT IN
5
RATE
13
SAMPLE IN
2
CYCLE OUT
3
RIGHT OUT
12
HOT COUPLER
15
RUN IN
14
SAMPLE SW
6
CV IN
7
CV ATTEN.
- Basic Operation
Left side /// SMOOTH mode
In CYCLE mode (switch down or CYCLE OUT connected to IN), the OUT produces a nice triangle wave. The
RATE knob controls an enormous frequency range of appr. 26s/CYCLE to appr. 20(!) kHz. Turning the CYCLE
mode on via the switch disables the IN.
In INPUT mode (CYCLE mode is off), the OUT follows the IN as quickly as the RATE parameter allows. A high at
the HOLD input will freeze the OUTPUT.
Right side /// STEPPED mode (and more)
The right side also has a CYCLE mode (switch down or CYCLE OUT connected to IN). However, the OUT
depends on the Sample (SMPL) input and the corresponding MODE switch as well as on the RUN input:
• Smooth Mode: Set the SMPL switch to center to let the right side run freely - both the SMPL input and
the RUN input are ignored. The Stepped side now pretends to be “smooth”, producing a triangle wave at
the OUT. The RATE knob controls a frequency range of >1min/CYCLE to 8 kHz.

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A PULSE wave (orange) into SMPL or RUN does not affect the Cycle.
• Sample Mode: When the SMPL switch is up, the GTO moves (cycles) only for a very short period of time
when a pulse wave triggers the SMPL input - irrespective of the pulse length:
A PULSE wave (orange) into SMPL allows the GTO to run for a moment before being frozen again.
If the RATE is very fast, the few full cycles can occur before being frozen again.
The moment in which the waveform can run freely is xed in length (about 0.5ms) - this limits the maxi-
mum speed the SMPL input can digest - if the clock signal is faster that about 2.2kHz, no more
triggering occurs and the waveform goes at (i.e. the CYCLE dies).
• INV Mode: When the SMPL switch is down, the SMPL input works exactly the other way around: the
GTO is free except for that small moment when the trigger occurs:
The CYCLE is held for a brief moment.

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• RUN Mode: If all of this is not exible enough gor you, the RUN input comes into play. Here, the GTO
runs freely while the signal is high and is held when the signal is low, i.e. the duty cycle of the pulse signal
determins the ratio of running to stopping. The RUN mode gives you essentiall a SMOOTH mode with
HOLD:
The CYCLE is running as long as RUN is low.
In INPUT mode (CYCLE mode is off), the OUT of the right side of the GTO tries to follow the IN as quickly as the
RATE parameter allows, with the restaints set by the SMPL mode.
• If the SMPL switch is in center position, SMPLE in and RUN are ignored, the right side is in SMOOTH
MODE (without a HOLD).
• Sample Mode: When the SMPL switch is up, the GTO moves only for a very short period of time when a
pulse wave triggers the SMPL input - irrespective of the pulse length.
High clock rate into SMPL (green) and a fast RATE creates quantizing / aliasing / bitcrushing (yellow) of the input signal (orange).
• INV Mode: When the SMPL switch is down, OUT is almost like in SMOOTH MODE, but the SMPL input
halts the signal for a very short moment:
Note the tiny step in the OUT (yellow) whenever SMPL IN goes high (orange). Green is the IN signal.

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• RUN Mode: Here again the signal is frozen as long as the RUN input is high - the GTO acts like the left
side (SMOOTH MODE with HOLD):
GTO (yellow) acts as in SMOOTH mode, RUN (orange) acts like HOLD.
Please note that RUN and SMPLE IN can be combined for even more complex waveforms and modulations:
GTO output (yellow) as affected by RUN (green) and SMPL (orange).

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IN
HOLDCYCLE
1V/OCT 1V/OCT
CYCLE
OUT OUT
VC RATERATE VC RATE RATE
GTO
IN
SERGE MODULAR
SYNC RUN
COUPLER
SMPL
INV
3
LEFT OUT
1
INPUT
8
1V/OCT IN
5
RATE
4
HOLD IN 2
CYCLE OUT
11
COUPLER OUT
9
SYNC IN
10
CYCLE SW
6
CV IN
7
CV ATTEN.
1
INPUT
8
1V/OCT IN
5
RATE
13
SAMPLE IN
2
CYCLE OUT
3
RIGHT OUT
12
HOT COUPLER
15
RUN IN
14
SAMPLE SW
6
CV IN
7
CV ATTEN.
1V/Oct Input (#8)
Each side of the GTO can be used as an audio source/oscillator (in SMOOTH MODE) and has an additional CV
input that has been calibrated to follow the 1V/Oct standard. Both sides are temperature compensated and
track 5 octaves or more (up to 2 kHz or above).
Sync Input (#9)
As you’d expect, the SYNC input causes the waveform (CYCLE) to restart. In the audio range, this gives you a
typical Sync effect, however, the SYNC also works far below audio in the CV range and allows you to reset the
GTO as an LFO.
The Coupler (#11, #12)
The COUPLER is an internal comparator comparing the outputs of both side.
Whenever the right side is HIGHER in voltage than the left side, the output of the COUPLER goes HI. Otherwise the
output is LO. The COUPLER has two outputs, one of which switches between 0V and +12V, the other switching

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between -12V and +12V. This is useful for generating complex control voltages and for patching a random voltage
generator. In fact, the Random Voltage Generator module is a Smooth & Stepped Generator internally patched
to function exclusively as such. Note that a Noise Source is needed for use of the GTO as a random voltage
generator. The red COUPLER OUT (11) is 0 to 5V, the black (“hot”, 12) one goes rail to rail (roughly -12V to +12V
i.e. 24V pp). Please be careful when using the black Coupler, e.g. when routing to a ADC converter or similar.
GTO - First Steps
The SSG is a complex, highly versatile module which allows for a wide range of uses and abuses both in the
audio and CV range, so it may require some time and experimenting to familiarize oneself with it - don’t expect
the module to reveal its secrets and power in a few minutes after you rst power it up. Here are some very basic
ideas to start with:
1. Patch the Smooth side of the SSG to cycle by connecting the Cycle jack into the Input. The euro-rack
version provides a Cycle switch to achieve the same. The Smooth side then produces a triangle wave
from about 0V to 5 V (aplitude slightly depends on frequency), the LED should indicate that. The Rate pot
determines the frequency of the cycle / output - the range is very wide, going from below 1 Hz to appr. 4
kHz. The Cycle jack provides a corresponding Pulse wave output.
2. Set the Stepped side to cycle as well by patching Cycle to IN (or turning on the Cycle switch in the
eurorack module). Unlike the Smooth side, the Stepped side will not generate an output in Cycle mode
(=LED stays dark or seems frozen) unless a Puls wave is fed into the Sample jack. Patch a pulse wave
- e.g. the Cycle output of the Smooth side - into the Sample jack to bring the stepped side to life. The
stepped side is essentially a sample-and-hold circuit, the Rate knob determines how long each step is at
the Stepped output. Changing the frequency of the pulse going into the Sample input and/or changing
the Rate affects the output.
3. The Smooth Side can be used as a Lowpass lter. Feed an audio signal (e.g. a saw or pulse wave from
an oscillator) into the In jack (Cycle switch turned off) and listen to the signal coming from the Smooth
out while you turn the Rate knob. At maxium position (full CW) the signal should sound pretty much un-
ltered, turning the Rate down (counterclockwise) the harmonics get ltered / smoothed out, at minimum
position the signal will disappear altogether.
Using the VC input jack in the same setup as before, this lter effect can be used to achieve the effect of a
Lowpass Gate / VCA. Send an CV envelope (e.g. from a DUSG or an Extended ADSR module) into the VC
jack and turn the VC knob sufciently high. Tune the Rate pot to a position so that the output is silent when no
CV is applied but clearly audible when the envelope is high. This causes a VCA effect, but the envelope not only
determines the amplitude, but also the amount of ltering applied (like a lowpass gate).
4. Try whatever you can think of and try not to distinguish between CV and audio - while originally the SSG
was primarily for control voltages, very interesting results can be found by going into audio range.

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Serge GTO - Patch Ideas
Sync’d VCO
Using both sides combined as one tracking oscillator.
• CYLCE both sides of the GTO.
• Set SMPL switch to center (“free”).
• Keyboard 1V/OCT left and right 1V/OCT of the GTO.
• Adjust the RATE of the left side to tune the left side to be one octave (or 2 octaves, or 5 semitones or ...)
higher than the right side.
• Right CYCLE out left SYNC input.
• Listen to left OUT or red COUPLER.
Metallizing VCA
Use a PCO or NTO (or another GTO) as a sound source, the right side of GTO as lter / VCA, however, scrambled
by the left GTO:
• SAW (or PULSE, TRI) GTO right side IN.
• CYLCE left side of GTO
• CYCLE out (left) RUN on the right
• Keyboard 1V/OCT PCO 1V/OCT and left GTO 1V/OCT
• Keyboard GATE OUT ExtADSR (or DSG) for Envelope
• ExtADSR OUT VC RATE of right GTO, VC RATE attenuverter fully CW
• right GTO: Rate knob at about 40%
Variations:
1. SYNC: Send PULSE OUT of PCO to GTO SYNC input.
2. (b) Send 2nd output of PCO to 1V/Oct of right GTO
3. (c) Send envelope from ExtADRS also to VC-RATE of GTO (left), VC-RATE attenuverter near center.
Geometric Waveshapes:
• Send a SAW wave from a PCO or NTO or DSG GTO left side SYNC and GTO right side SMPL.
• Keyboard 1V/OCT PCO 1V/OCT and left GTO 1V/OCT
• CYLCE left side of GTO
• Do not CYLCE right side of GTO
• CYCLE out (left) IN on the right

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• Set SMPL switch to SMPL (top)
• RED Coupler RUN on the right
• Keyboard GATE OUT ExtADSR (or DSG) for Envelope
• ExtADSR OUT VC RATE of right GTO, VC RATE attenuverter fully CW
• Right GTO: Rate knob at about 50%
• Listen to right GTO OUT.
SYNC FM
• CYLCE both sides of the GTO.
• Set SMPL switch to Cycle (center) or INV
• Right OUT  left VC RATE (RATE attenuverter set to about 2 p.m.)
• Keyboard 1V/OCT both left and right 1V/OCT (but don’t expect the patch to track!)
• Right CYCLE out  SYNC
Variations:
• Send left GATE OUT to RUN and set SMPL switch to SMPL or INV
SYNC DRONE
Again, using both sides combined as one massive oscillator.
• CYLCE both sides of the GTO.
• Left CYCLE  RUN
• Right CYCLE out  SYNC
• Right CYCLE out  right VC RATE
• Set SMPL switch down (“INV”).
• Keyboard 1V/OCT left and right 1V/OCT of the GTO.
• Adjust the RATE of the left side to tune the left side to be one octave (or 2 octaves, or 5 semitones or ...)
higher than the right side.
• Send ADSR or LFO to left VC RATE with VC RATE knob close to center.
• Alternatively, send black COUPLER to left VC RATE with VC RATE knob close to center.
• Use right RATE knob to adjust pitch.
• Listen to left OUT (green) or red COUPLER (orange) - yellow wave is a mix of left OUT and COUPLER:

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DUAL GTO Patches
These patches use 2 GTOs, here named A and B for convenience.
Double SYNC:
• CYCLE both left sides (SMOOTH).
• B: CYCLE out (left) A: SYNC In
• A: CYCLE out (left) B: 1V/Oct
• Option: A (going SAW instead of TRI): CYCLE out (left) A: CV IN, CV-Attenuverter close to center
• Play with RATE knobs on A and B.
SSG mk2 + Noise patch #2
• CYLCE left side of GTO
• Coupler (normal) Stepped RUN and Smooth SYNC
• Keyboard 1V/Oct input
• SH/SRC Stepped IN
Listen to whatever output ;-)
(Version 10 March 2023)
SERGE Modular by Random*Source. Under license and in cooperation with Serge Tcherepnin. All rights reserved.