Vaux Electronics BS-400A User Manual
Unbalanced/Balanced Converter Modules
BZ-400A, BS-400A, and BX-400A
Vaux Unbalanced-to-Balanced audio converter modules allow installers to extend
audio paths up to 1000 feet (300 meters) using balanced signals, eliminating
powerline hum and other noise problems encountered when running unbalanced
signals over long distances. Vaux balanced converters use a high-fidelity, low-
noise active design, and there is no signal loss from end to end -- the converters
translate signal levels between the unbalanced -10 dBV and the balanced +4 dBu
audio standards.
There are three models of converter modules covered by this installation note: BZ-
400A, BS-400A, and BX-400A. All of these converters have four stereo channels
(or a total of eight mono channels), in different configurations.
The BZ-400A converts four stereo unbalanced audio signals to balanced audio, and
is typically connected to the zone outputs of a Vaux matrix switcher, for driving
balanced powered speakers, or remote amplifiers. It can also be used with remote
sources, for driving balanced signals back to the switcher.
The BS-400A converts four stereo balanced audio signals to unbalanced audio, and
is typically connected to the source inputs of a Vaux matrix switcher, for receiving
balanced signals from remote sources. It can also be used with remote amplifiers,
for receiving balanced signals from the switcher.
The BX-400A converts two stereo audio signals from unbalanced to balanced, and
two stereo audio signals from balanced to unbalanced. It is typically used at the
switcher to drive two balanced zones, and receive two balanced sources.
The converters use phono connectors for the unbalanced line-level audio
inputs/outputs, and 5-position removable Phoenix(r) terminal plugs for the balanced
line-level audio inputs/outputs. Unbalanced signals connect using short coaxial
patch cables, and balanced signals connect using either unshielded-twisted-pair
(UTP) cable (CAT-5 cable is recommended), or shielded-twisted-pair (STP) cable
(eg: Belden 8737). Up to 1000 feet (300 meters) of UTP cable, or up to 500 feet
(150 meters) of STP cable may be used .
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Unbalanced and balanced audio systems use different references for their nominal
volume level:
The nominal level for unbalanced signals is -10 dBV. The unit dBV, is a voltage
level with respect to 1 Vrms. A nominal -10 dBV signal is 0.316 Vrms from
center pin to ground (-10 = 20log(0.316/1)).
The nominal level for balanced signals is +4 dBu. The unit dBu, is a voltage
level with respect to 0.775 Vrms. A nominal +4 dBu signal is 1.23 Vrms from
+ to - terminals (+4 = 20log(1.23/0.775)).
An older reference is dBm, which is 1 mW into 600-ohms -- this came from days
when balanced signals used 600-ohm transformer coupling, a lossy conversion,
which limits bass response. Sometimes dBm is used in specs of balanced systems
that are not 600-ohm impedance -- this is incorrect. Transformer-coupled systems
use 600-ohm output and input impedances, for maximum power transfer over
these lossy links.
Most electronic balanced systems today use a low output impedance and a high
input impedance, for minimum voltage loss, and amplify/attenuate as needed for
the conversion. Vaux converters maintain nominal signal levels, that is, -10 dBV
is amplified to +4 dBu, and vice-versa. This is not a 14-dB difference -- since
there are different reference levels, there is electrically just an 11.8 dB difference,
which is what Vaux converters provide.
Installation
The BZ-400A is installed near the matrix switcher (or other unbalanced signal
output). Connect four stereo unbalanced audio zone outputs to the UNBAL inputs
on the BZ-400A, using audio patch cables. Connect the balanced audio cables to
the BAL outputs, and run the cables to the remote location(s). If using CAT-5 cable,
connect one pair to the BAL left +/- terminals, and a second pair to the right +/-
terminals -- note the wire colors you choose, and connect these appropriately at the
other end of the cable. If using STP cable, connect the left/right pairs, BUT do not
connect the cable shield to the center ground (G) terminal -- the cable shield should
only connect to the ground terminal at the receiving end of the cable.
The BS-400A is installed near the matrix switcher (or other unbalanced signal
input). Connect four stereo unbalanced audio source inputs to the UNBAL outputs
on the BS-400A, using audio patch cables. Connect the balanced audio cables
from the remote location(s) to the BAL inputs. If using CAT-5 cable, connect
one pair to the BAL left +/- terminals, and a second pair to the right +/- terminals
-- note the wire colors you choose, and connect these appropriately at the other
end of the cable. If using STP cable, connect the left/right pairs, AND also
connect the cable shield to the center ground (G) terminal -- the cable shield
should only connect to the ground terminal at the receiving end of the cable.
The BX-400A is installed as noted above for the BZ and BS units. Note that the
unbalanced inputs are UNBAL-1 and UNBAL-2, while the balanced inputs use
BAL-3 and BAL-4 (this is also noted on the rear-panel label).
Note: The balanced shield ground (G) terminals are connected to chassis ground.
The signal ground for the unbalanced signals is connected internally to the chassis
ground via a wire jumper. If there is a need to float these two grounds, this jumper
may be cut -- contact the factory before doing this.
Technical Note