Studio Technologies 45DC - Manual (Page 7)

Model 45DC User Guide Issue 1, January 2015
Studio Technologies, Inc. Page 7
A significant capability of the Model 45DC’s
two party-line intercom interfaces is their
ability to supply DC power and 200 ohm
AC terminations to “create” two indepen-
dent intercom circuits. The 28 volt DC
output can power user devices such as
beltpacks. With up to 150 milliamperes
(mA) of current available, a typical enter-
tainment application could connect up to
three RS-501 or five RS-701 beltpacks to
each of the Model 45DC’s two interfaces.
In many applications this can eliminate the
need for an external intercom power sup-
ply, thereby reducing total system cost,
weight, and required mounting space. The
power supply outputs are monitored for
over-current and short-circuit conditions.
Under firmware (embedded software)
control the outputs will automatically cycle
off and on to help prevent damage to the
circuitry and connected equipment.
Dante Audio-over-Ethernet
Audio data is sent to and from the Model
45DC using the Dante Audio-over-Ethernet
media networking technology. Audio
signals with a sample rate of 48 kHz and
a bit depth of up to 24 are supported.
Audio input (receiver) and output (transmit-
ter) channels on associated Dante-enabled
devices can be assigned to the Model
45DC using the Dante Controller software
application. This makes selecting the way
in which a Model 45DC fits into a specific
application a simple matter.
Analog Hybrids with Auto
Nulling
Two circuits referred to as “hybrids” inter-
face the Dante input and output channels
with the two party-line interface channels.
The hybrids provide low noise and distor-
tion, good frequency response, and high
return-loss (“nulling”), even when presented
with a wide range of party-line conditions.
Unlike telephone-line (“POTS”) oriented
DSP-based hybrid circuits, the Model
45DC’s analog circuitry maintains extended
frequency response. With a passband of
100 Hz on the low end and 8 kHz on the
high end, natural-sounding voice signals
can be sent to and received from a party-
line circuit.
The Model 45DC’s sophisticated hybrid
auto nulling function uses a combination
of digital and analog circuitry under micro-
processor control to achieve significant
trans-hybrid loss. This return-loss “null” is
achieved by making a series of firmware-
directed adjustments to account for the re-
sistive, inductive, and capacitive conditions
that are present on the connected party-line
cabling and user devices. Whenever one
of the Model 45DC’s auto null buttons is
pressed digital circuitry adjusts the associ-
ated hybrid to achieve its maximum return-
loss in less than 15 seconds. While the
nulling process is automatic, it only takes
place upon user request. The resulting
null parameters are stored in non-volatile
memory.
Pro Audio Quality
The Model 45DC’s audio circuitry was de-
signed in the spirit of professional
audio equipment rather than that found
in typical party-line intercom gear. High-per-
formance components are used through-
out, providing low-distortion, low-noise, and
high headroom. Using passive and active
filters the frequency response of the audio
channels is limited to nominally 100 Hz to
8 kHz. This range was selected to provide
excellent performance for human speech
while maximizing the ability of the hybrid
circuits to create substantial “nulls.”