RYO Optodist User manual

LjunggrenAudio RYO Optodist:
an OptoVCA with distortion and LED limiting.
Quickstart – what is the Optodist and how do I get going?
The Optodist is a compact, easy to use, easy to build and great sounding
distortion module which will also work as a VCA if desired. Consisting of a
oltage controlled amplifier based on a pair of Silonex/Ad anced Photonix
optocouplers that allow a characterful o erdri en sound and plucky dynamic
response to CV, it is as equally at home “crisping up” highs and mids or warming
up your lows as it is at turning a resonant filter into a howling beast or your
drums into crushing carnage.

Installation
To begin installation, please make sure that:
-you ha e a standard pinout eurorack bus board
- you ha e +12V and -12V power rails on that bus board [no +5V supply is
required]
- the power rails are not o erloaded
!!!Be ore installing this module disconnect the power rom your system!!!
- Double check the polarity of the ribbon cable - The red stripe should be
aligned with the -12V rail, on both the module and on the bus board
[we use shrouded headers but it's still possible a cable has been assembled
with the stripe on the wrong side of the shroud so always double check!].
Also make sure when using busboards without shrouded headers that the pins
aren't transposed a row ertically or horizontally – all pins should insert into
holes on the cable.
Although we use both PTC fuses and schottky diodes to pro ide re erse polarity
and excess current protection, we do not take any responsibility for damages
caused by wrong power supply connection!
After you ha e connected e erything, double checked it and ensured your case is
closed such that no power lines can be touched by your hand or any stray cables
drop into holes, turn on your system and test the module

We designed the Optodist using SR3 optocouplers; the SR3's gi e a tighter,
snappier CV response and ha e less bleed through of the signal when gain is
fully off and signal in is set to low settings for a somewhat clean signal or
lighter distortion effect.
Please note that due to the nature of the actrol-style optocouplers, response
beha iour may ary between different factory batches.]
Also on board is an LED limiter circuit which soft-clips the signal through a
set of 4 LEDs ( isible on the front panel), for adding a different fla our
to your distortion. the choice of LEDs is up to you, experimenting with
different types will affect the sound.
Two colours of LEDs were used and tested in de elopment of the Optodist,
green being standard but also some in estigations into yellow were made that
re ealed that it has a subtly brighter tone and is much brighter isually as
well. Any 3mm LEDs from infra red up to piercing bright white or iolet will
work, although there may need to be an adjustment to a resistor alue to get the
correct brightness.
The Optodist is a novice- riendly project, it is a low part count, single-PCB
build that only requires the most basic experience in PCB soldering and
module assembly:
The ampli ier has an exponential response to control voltages; and accepts
between 0V and 8V c by default. The amplifier accepts both DC and AC signals,
though it should be noted that due to the slew rate of the optocouplers, audio
rate modulation of the gain CV is limited in frequency to a degree dictated by
the choice of either SR2 or SR3 optocouplers.
The module has one audio input and one audio output; the signal in knob
dictating the audio input le el. The VCA has a control oltage input with
attenuator (gain CV), and manual gain control which sets either the VCA initial
open le el and/or the amount of o erdri e gain.
The module can be used as a basic attenuator; by disconnecting c /keeping gain
c fully CCW, and adjusting the signal in and gain control as desired.
When the cv input is presented with a control voltage between 0V and 8V, in
this setup, the module will behave as a traditional relatively clean
sounding VCA; albeit with some character and limitations as dictated by the
optocouplers.
Depending on your calibration settings and choice o optocouplers, opening
either the 'signal in' knob and/or opening the 'gain' knob past approximately
50% will introduce distortion; this distortion will ary in character
depending on the settings, but can be tamed by engaging the LED clipping
circuit, although this will further alter the character of the distortion.
(when gain is between fully off [CCW] and 50% the module can be used as an
attenuator or as a relati ely clean VCA where gain dictates the VCA initial
le el; opening the 'gain' knob past approximately 50% will introduce
distortion - from 50% up to max gain (full cw) the Optodist will boost the
signal with increasing distortion).

Dimensions
Height: 3U [128.5mm],
Width: 6HP [30mm],
Depth: 31mm (with power cable attached)
Weight: 30g (approx w/cable)
Current consumption
+12V rail min 13mA to max 16mA
-12V rail min 13mA to max 16mA
+5V rail no +5V supply required
[There are small power ariations between different actrol and LED arieties.
The option requiring least power is SR3 optocoupler paired with green limiter
LEDs.]
Basic speci ications
total frequency controllable range dc to 50 kHz
max input/output audio signal 20 Vpp
CV input range (calibrate to preference) 0V to +10V max
Max gain 0dB gain with +8V @ c input
(calibrated as VCA) -40dB gain with 0V @ c input
Nominal impedances
Audio signal input: 100k ohm
Audio Signal output: 1k ohm
CV input: 100k ohm

patches that ha e been used in the ideos; and, as e er, experiment – RYO
modules are designed with all necessary protection and fail-safes so you can
just start plugging in patch cables and see what happens!
ping it:
many modules with actrols in the CV-path can be 'pinged' – excited by a
short spike of CV such as a trigger or by a few ms pulse of noise, the
actrols will ring with a ery natural, organic sounding, woody decay –
great for drums or percussi e tonal instruments.
distort a cv signal:
try something different - such as distorting an FM modulator wa e so that
the resulting sound output from a carrier VCO/VCF/VCA is wildly
different.
Audio Routing: CV Routing:
Braids out to Optodist in uLFO sine out to Cold Mac 'Slope' in
Optodist out to Ripples in.Cold Mac 'recti ied out' Stackabled*
Ripples lowpass out to output to both Optodist CV in and Braids
'Timbre' in [green input]
*(multiples [mults] and other forms
of signal splitters can be used.)
Patch ideas:
Although uses of VCAs in patch examples and ideas are found readily online and
in some books, and similarly those familiar with using distortion effects
perhaps from the guitar pedal cultural background, there are many other less
ob ious ways to use the Optodist in patches in your modular rig:
below i' e included e erything from some inspiring words to links to ideos and
diagrams with popular modules used to perform necessary duties showing the