SALUT
Thank you for purchasing this Xaoc Devices
product. Ostrawa
[ɔs’trava]
is a fully ste-
reo four-channel voltage-controlled mixer
featuring a stereo mixing bus, one stereo
auxiliary send per channel (switchable be-
tween pre and post-VCA) with stereo returns,
clickless muting, individual level meters, and
a super-clean and DC-coupled signal path
designed with high-quality VCA and opamp
chips. We have carefully crafted Ostrawa's
voltage control response to achieve what
we believe to be the optimal user experience
found in a Eurorack mixer. The design fea-
tures an elaborate control circuit that com-
bines the internal voltages generated by the
panel potentiometers with external CV over
volume and stereo balance. The result is a
natural attenuator response that constrains
VCA gain to a usable range while minimizing
distortion. Ostrawa, a sister module to Xaoc
Devices Praga, features similar response
characteristics and layout of controls with
some functional differences due to its stereo
inputs and limited panel space. Multiple Os-
trawa and Praga units may be chained for a
custom configurable mixing system.
To better understand the device and avoid
common pitfalls, we strongly advise the user
to read through the entire manual before us-
ing the module.
INSTALLATION
The module requires 20hp worth of free space
in the Eurorack cabinet. The ribbon type pow-
er cable must be plugged into the bus board,
paying close attention to polarity orientation.
The red stripe indicates the negative 12V rail
and should align with the dot, –12V, or red
stripe marks on both the unit and the bus
board. The module itself is protected against
reversed power connection; however, reversing
the 16-pin header
may cause serious dam-
age
to other components of your system by
short-circuiting the +12V and +5V power rails.
Unless you are using Ostrawa with the Bo-
humin expander, make sure the factory-in-
stalled jumpers are present on the bohumin
expander 2 header as indicated on the PCB.
The module should be fastened by mounting
the supplied screws before powering up.
MODULE OVERVIEW
Ostrawa's front-panel topology (see fig. 1)
resembles a typical mixer with four identical
channels. The vol knobs
1
allow for manual
control of each channel's respective level. The
bal knob
2
adjusts the channel's position in
the stereo panorama. The aux send a knob
3
adjusts the amount of stereo signal (pre or
post-VCA) sent to the auxiliary outputs. The il-
luminated active|aux pre button
4
allows
the user to mute the channel and switch be-
tween two of effect send modes. The five-bar
LED level indicator
5
displays each channel's
post-fader level of combined left+right sig-
nals. The lower section contains pairs of jacks
for signal inputs
6
, and CV inputs for bal
7
and vol control
8
.
The bottom row of sockets is common to all
four channels and offers pairs of sum out-
puts
9
, stereo aux send a outputs
10
,
2
module
explained
