Model 545DC User Guide Issue 1, June 2022
Studio Technologies, Inc. Page 7
Model 545DC
INTERCOM INTERFACE
A significant capability of the Model 545DC’s two
party-line interfaces is their ability to supply power
and a 200 ohms AC termination to “create” two inde-
pendent intercom circuits. Each 28 volts DC output
can power a moderate number of devices such as
user beltpacks. With up to 150 milliamperes (mA) of
current available, a typical entertainment application
could connect up to three RS-501 or ve RS-701 belt-
packs to each of the Model 545DC’s two interfaces. In
many applications, this can eliminate the need for an
external intercom power supply, reducing total system
cost, weight, and required mounting space. The power
supply outputs are monitored for over-current and
short-circuit conditions. Under rmware (embedded
software) control the outputs will automatically cycle
o 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 545DC
using the Dante audio-over-Ethernet media network-
ing technology. Audio signals with a sample rate of
48 kHz and a bit depth of up to 24 are supported.
Audio transmitter (output) and receiver (input) chan-
nels on associated Dante-enabled devices can be
routed (subscribed) to the Model 545DC using the
Dante Controller application. This makes it simple
to select the way in which a Model 545DC ts into a
specic application.
Analog Hybrids with Auto Nulling
Two circuits, referred to as “hybrids,” interface the
Dante transmitter (output) and receiver (input) chan-
nels with the two party-line channels. The hybrids
provide low noise and distortion, 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 545DC’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 545DC’s sophisticated hybrid auto nulling
function uses a combination of digital and analog
circuitry under microprocessor control to achieve
signicant trans-hybrid loss. This return-loss “null”
is achieved by making a series of rmware-directed
adjustments to account for the resistive, inductive, and
capacitive conditions that are present on the connect-
ed party-line cabling and user devices. Whenever one
of the Model 545DC’s auto null buttons is pressed,
or the STcontroller application is used, digital circuitry
adjusts the associated hybrid to achieve its maximum
return-loss in under 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 545DC’s audio circuitry was designed
in the spirit of professional audio equipment rather
than that found in typical party-line intercom gear.
High-performance components are used throughout,
providing low-distortion, low-noise, and high head-
room. Using active lters, 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.”
Audio Meters
The Model 545DC contains two sets of 5-segment
LED level meters. Each set of two meters displays the
level of the signals being sent to and received from
a party-line interface. At the time of installation and
setup the meters are invaluable in helping to conrm
correct operation. During normal operation the meters
oer rapid conrmation of audio signals owing in to
and out of the Model 545DC unit.
Status Display
LED indicators are provided on the Model 545DC’s
front panel, oering a status indication of the party-
line power sources, party-line activity, and auto null
functions. Two other LEDs oer a direct indication of
what source or sources of power are connected to
the Model 545DC. The STcontroller application also
provides a real-time “virtual” status display of the unit’s
PL power sources, PL activity, and auto null functions.
Call Light Support
Typical single-channel party-line intercom circuits
provide a call light function by way of a DC voltage
applied to the audio path. The Model 545DC can de-
tect such call light activity, converting it to a 20 kHz
audio tone which is then transported over the Dante
