Random*Source SERGE MODULAR AUDIO INTERFACE 2023 User manual

SERGE
AUDIO INTERFACE
2023
USER MANUAL
V1.0
RANDOM*SOURCE

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Audio Interface
Installation ........................................................ 3
Overview ......................................................... 3
The Audio Interface ................................................. 4
Preamp .......................................................... 5
Compressor ....................................................... 5
VCA ............................................................. 5
Analyzer / Envelope Detector / Gates .................................... 5
Equal Power XFader ................................................. 6
CV Processor ...................................................... 7

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Audio Interface
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 Audio Interface 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 SYSTEM OFF before installing the module. Please use the power cable provided to connect the
small end of the power cable to the module.
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 Audio Interface 4x4 module comprises (from left to right) the Audio Interface, an Equal Power X-Fader
with balanced Output and a CV-Processor. The Audio Interface section on the left contains:
• Preamp Section
• Compressor Section with Sidechain input
• VCA section with Envelope Detector (RMS) and 2 variable Gates.

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The Audio Interface
TRS Balanced Input (Mic, Guitar, Instruments)
Line Input (consumer level, fixed amplification)
LED indicates that Preamp Out > 5Vpp
Preamp Out
Compressor Input (expects 5Vpp)
Sidechain Input (active when switch is down)
Compression Amount
VCA (exponential) Input / CV Input / VCA Out
Envelopelope Follower (CV) Out
Gated Envelope (CV) Out
HIGH Comparator Gate Out
LOW Comparator Gate Out

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Preamp
The purpose of this preamplier is to bring external signals (dynamic mic, Guitar or other instruments) to the Serge
Audio level of 5Vpp. The LED lights up when the signal reaches (or exceeds) 5Vpp.
The Preamp offers two parallel inputs, one line level input (mono minijack) with a xed amplication of approx.
x8 and one TRS balanced input (6,35mm TRS) with up to +60dB.
Compressor
The compressor reduces the dynamic range of the incoming audio signal. Its knob continuously adjusts gain,
threshold and compression ratio. It works best with 5Vpp signals.
The internal RMS detector derives an envelope control voltage from the input signal, which is available at the
ENV OUT. Note: When SIDE CHAIN is activated the enevlope is derived from the side chain signal!
VCA
This high quality audio VCA is controlled by the GATED OUT CV (see below), but offers an additional CV input for
external control.
Analyzer / Envelope Detector / Gates
ENV OUT (grey line) provides a control voltage reecting the envelope of a signal running through the compressor
(using an RMS envelope detector).
UPPER
THRESHOLD
LOWER
THRESHOLD
0V
GATED OUT (blue line) controls the VCA. It is based on this envelope signal (CV), but two additional gates
are applied that can be used hard limit the CV signal. The UPPER THRESHOLD knob works as limiter (or
volume control) and prevents the CV signal from exceeding the threshold. The LOW THRESHOLD knob kills the
envelope (i.e. sets it to 0V) as long as it is below the theshold. This can be used like a noise gate in combination
with the VCA.

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Equal Power XFader
The XFader is an equal-power, crossfader combined with a special VCA.
The audio signals sent into IN 1 and IN 2 are being AC coupled and then sent into the
crossfader. The XFade knob and the CV input above determine the ratio between IN 1
and IN 2.
The blended signal runs through a VCA and is then available in the OUT section - in form
of a banana jack for further patching or a balanced output (TRS, 6.35mm).
The output level is set via the GAIN knob and the corresponding CV input. The VCA
provides a lot of gain, allowing heavy clipping / distortion (e.g. turning a sine wave
into a square wave). However:
BE CAREFUL: Gain allows massive amplication, especially when using knob +
CV - so that the resulting signal may easily reach 24Vpp, which may be too much
for external gear (AD-converters, mixers) to handle! Watch the knopb setting /
output level before sending the resulting signal to sensitive equipment.

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CV Processor
The CV-Processor is a DC-coupled mixer with a few details that are not obvious:
IN 1 acts like a normal mix input with the knob being an attenuator, however when no
cable is connected, the IN 1 knob adds a DC offset up tp about 5V.
IN 2 is a regualr input with attenuator.
IN 3 may look like a regular input, but is actually a CV processor where the knob acts
as an attenuverter, i.e. a 0 to 5V sawtooth signal send in is being inverted when the
knob is fully CCW and is blocked (attenuated) at center position of the knob.
In combination with the Offset function of channel 1 (with no cable attached), IN 3 (with
the knob turned to the left) allows to subtract channel 3 from a xed level (offset) which
can be used for ducking effects etc.
AUX IN provides an additional channel without attenuation.
(Version 13.07.23)
SERGE Modular by Random*Source. Under license and in cooperation with Serge Tcherepnin. All rights reserved.
SERGE is a registered trademark.