Xaoc Devices Bohumin User manual

BOHUMIN
mixing console
commander
Model of 1966
operator’s manual rev. 1966/X/1.0

SALUT
Thank you for purchasing this Xaoc Devices
product. Bohumin [bo'xumin] is an expander
for our Ostrawa full stereo mixer module. By
connecting to Bohumin, Ostrawa gains a sec-
ond full stereo AUX bus with voltage control
over the amount of the effect on each channel.
In addition, Bohumin features manual atten-
uators for stereo returns of both aux a (note:
the send and return jacks for aux a are locat-
ed directly on Ostrawa) and aux b, as well as
four gate inputs for automated clickless mut-
ing of each stereo input channel.
Bohumin should be installed alongside a sin-
gle Ostrawa unit. Please note that Bohumin
is not compatible with Ostrawa's sister mod-
ule Praga. Similarly, Praga's expander, Hrad,
cannot be connected to Ostrawa. However, it
is possible to chain any combination of Os-
trawas and Pragas, and each of them may
have its corresponding expander attached. In
such a setup, the signals of the main mixing
buses and AUX returns are all passed down-
stream to the last unit in the chain (preferably
Praga with Hrad as the output module).
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 10hp worth of free space
in the Eurorack cabinet. Bohumin does not
have a separate power connection; instead,
it draws power from Ostrawa and adds
+50mA/-40mA to Ostrawa’s power consump-
tion.
attention: never connect a power ca-
ble to any pin header on the back of
your bohumin; it will destroy the unit!
Bohumin connects to Ostrawa using one 16-
pin and one 10-pin ribbon cable, both sup-
plied with the unit. Note that these cables
are deliberately short for safety and to keep
noise and interference low and should not be
replaced with longer ones. Bohumin should be
located next to your Ostrawa. Before making
the connection, you need to remove the 2-pin
jumpers from the lower pin header of your
Ostrawa. Keep them for later use, as you will
have to put them back if you ever decide to
use Ostrawa without Bohumin; otherwise,
the AUX return will not work properly. Next,
carefully connect the cable going from the
upper and the lower headers of Bohumin to
the upper and the lower headers of Ostrawa,
      
not mix them up or rotate them as this would
seriously damage both units!
Both modules should be fastened by mounting
the supplied screws before powering up.
MODULE OVERVIEW
      
is straightforward; however, due to space
limitations, the order of the potentiometers
differs from Ostrawa. The four aux b send
level knobs 1control the amount of stereo
2
module
explained

3
1
4 5
3
6
2 5
front panel
overview

the interface

4
auxiliary
buses
signal from each channel of Ostrawa to be
sent to the aux send b pair of jacks 2. The
amount of effect is also controlled by the cor-
responding four aux b cv inputs 3.
The two knobs situated in the middle of the
panel, aux ret a 4and aux ret b 5, are
stereo attenuators for the AUX returns, i.e., the
stereo signal pairs patched into aux return
aon Ostrawa and aux return b on Bohumin
respectively.
The four active jacks 6offer remote muting
and unmuting of the four stereo input chan-
nels in Ostrawa.
AUX BUSES
Please keep in mind that auxiliary effects op-
erate in parallel to the main summing bus of
the mixer, which means the processed signal
is added to the original signal and does not
replace it.
Ostrawa with Bohumin installed offers two
entirely independent full-stereo auxiliary
effect loops: aux a and aux b. aux a can be
switched between pre-VCA and post-VCA and
has manual control over the amount of send
and return (the return attenuator is added
with Bohumin). aux b is only post-VCA and
installation

5
expandability
& chaining
the amount of send can be controlled man-
ually and via the additional VCAs inside Bo-
humin. The corresponding inputs accept bi-
polar voltages. A CV of 0 to +8V increases the
amount of send relative to what is set with
the knob, while negative CV of 0 to -8V grad-
ually attenuates the signal even with aux b
sends level attenuators fully open.
ACTIVITY CONTROL INPUTS
By feeding gate signals to the four active
inputs in Bohumin, it is possible to remote-
ly control the opening and closing of each
channel in Ostrawa in the same way as click-
ing its front panel buttons. A gate ON signal
(about +2.4V or more) activates the channel,
while OFF (0V) mutes it (in a clickless way).
Even with the gate signal patched, the panel
buttons still remain operational; however,
unplugging the signal will leave your chan-
nel muted.
ACCESSORY
Our Coal Mine black panels are available for
all Xaoc Devices modules. Sold separately.
Ask your favorite retailer. •
signal flow
mute
aux B
send
balance
CV
volume
CV
aux B
send
aux a send aux a ret aux b ret
aux A
return
aux B
send
CV
aux B
return
block
diagram
main bus
aux bus
control
input Rinput L
Ostrawa Bohumin
pan vol
vu
aux
vca vca
vca
vca

FEATURES
Expander for
Xaoc Devices
Ostrawa mixer
Additional AUX B
effect loop
Full stereo sends
and returns
CV inputs for
controlling AUX
B sends
Return attenu-
ators for AUX A
and AUX B
Gate control in-
puts for clickless
channel muting
SPECIFICATION
Eurorack syn-
thesizer format
compatible
10hp wide,
31 mm deep
(including the
ribbon cable and
bracket)
Current drawn
from Ostrawa:
+50mA/-40mA
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