Studio Technologies 45DC User manual

Copyright © 2020 by Studio Technologies, Inc., all rights reserved
studio-tech.com
50017-0620, Issue 4
User Guide
Issue 4, June 2020
This User Guide is applicable for serial numbers
M45DC-00151 and later with application rmware 3.1 and later
and Dante rmware 4.6.0 (UltimoX2 4.2.2.3) and later
Model 45DC
Dante to Dual Party-Line
Intercom Interface

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Model 45DC User Guide Issue 4, June 2020
Studio Technologies, Inc. Page 3
Table of Contents
Revision History ............................................................ 4
Introduction................................................................... 5
Installation ..................................................................... 9
Conguration ................................................................ 12
Operation ...................................................................... 15
Technical Notes............................................................. 20
Specications................................................................ 25

Issue 4, June 2020 Model 45DC User Guide
Page 4 Studio Technologies, Inc.
Revision History
Issue 4, June 2020:
1. Documents deletion of pull-up/pull-down capability.
Issue 3, March 2016:
1. Documents new conguration that allows the party-line active detection function to be
disabled (added to application rmware version 3.1).
Issue 2, August 2015:
1. Documents enhanced unit identication feature (added to application rmware
version 2.5).
2. Adds improvements to IP address conguration assignment explanation.
Issue 1, January 2015:
1. Initial release.

Model 45DC User Guide Issue 4, June 2020
Studio Technologies, Inc. Page 5
Introduction
The Model 45DC Dante®to Dual Party-Line
Intercom Interface is designed for applica-
tions that utilize single-channel analog par-
ty-line (PL) intercom technology. The unit
provides two independent single-channel
interfaces that each support one party-line
audio channel. Single-channel party-line
intercom systems are commonly used in
theater, entertainment, and education appli-
cations where a simple, reliable, low-cost,
and easy to use solution is desired. Analog
party-line products from Clear-Com®are
directly compatible with the Model 45DC.
The Dante Audio-over-Ethernet media
networking technology is used to trans-
port the send and receive audio channels
associated with each of the two party-line
circuits. Two hybrid circuits with automatic
nulling provide excellent audio quality and
high return-loss. (These hybrid circuits are
sometimes referred to as 2-wire to 4-wire
converters.) The Model 45DC is directly
compatible with the latest broadcast and
audio equipment that uses Dante technol-
ogy. An Ethernet connection is all that’s
required to make the Model 45DC part of a
sophisticated, networked audio system.
A Model 45DC can interconnect with devic-
es such as matrix intercom systems, DSP
processors, and audio consoles. The Model
45DC is directly compatible with the RTS
ADAM®OMNEO® matrix intercom network.
Alternately, two Model 45DC units can inter-
connect by way of the associated Ethernet
network. The Model 45DC can be powered
by Power-over-Ethernet (PoE) or an external
source of 12 volts DC. Two party-line power
sources with impedance termination net-
works can be supplied by the Model 45DC,
allowing connection of two sets of user belt-
packs such as the Clear-Com RS-501 and
RS-701. A Model 45DC can also connect
Figure 1. Model 45DC standard “throw-down” front view
Figure 2. Model 45DC back view

Issue 4, June 2020 Model 45DC User Guide
Page 6 Studio Technologies, Inc.
with one or two existing powered and termi-
nated intercom circuits. Audio level meters
provide conrmation of system performance
during setup and operation. Support for
transporting call light signals between Mod-
el 45DC units is also provided.
Standard connectors are used for party-line
intercom, Ethernet, and DC power inter-
connections. The Model 45DC’s enclosure
has a “1/2-rack” 1U form factor and weighs
less than two pounds, making it well suited
for use in portable applications. Alternately,
using one of the optional rack-mount front
panels, one or two Model 45DC units can
be mounted in a single space (1U) of a stan-
dard 19-inch rack enclosure.
Applications
There are two main ways that the Model
45DC can be used in applications. The rst
is to add party-line intercom support for
matrix intercom systems. The second is
to link two stand-alone party-line intercom
systems. Ports on matrix intercom systems
that support Dante, such as the RTS ADAM
with OMNEO, can be routed to the Model
45DC’s Dante receiver (input) and transmit-
ter (output) channels. The Model 45DC’s
circuitry will then convert these signals
into two single-channel party-line intercom
circuits. In this way, adding party-line sup-
port to RTS + OMNEO is a simple task. The
Model 45DC can also be used with matrix
intercom systems that don’t support Dante.
An external analog-to-Dante interface can
be used to convert analog intercom ports
to Dante channels. For example, the Model
44D Interface from Studio Technologies is
specically designed to work with matrix in-
tercom systems. Once in the digital domain,
these Dante channels can be interconnect-
ed with the Model 45DC’s audio input and
output channels.
Two separate sets of party-line intercom
circuits can easily be interconnected using
two Model 45DC Interfaces. At each end
a Model 45DC is connected to one or two
party-line circuits as well as the Dante
network. The Dante Controller applica-
tion will then be used to route the audio
channels between the two units. That’s
it — nothing else is required to achieve
excellent performance.
The Model 45DC can also be used to
“bridge” two single-channel party-line
intercom circuits with one 2-channel party-
line intercom circuit. This involves using
a Model 45DC for the two single-channel
circuits and one of the Studio Technolo-
gies Model 45DR Intercom Interface units
for the 2-channel circuit. The Model 45DR
is the “cousin” of the Model 45DC and
supports one 2-channel party-line inter-
com circuit rather than two single-channel
circuits. These 2-channel circuits, typically
supported by equipment from RTS, are
commonly used in broadcast applications.
Party-Line Interfaces
The Model 45DC’s two party-line intercom
interfaces are optimized for connection
with two single-channel party-line circuits
and user devices such as those associat-
ed with equipment from Clear-Com. (While
the Model 45DC will function in a limited
manner with a 2-channel RTS TW circuit,
the Model 45DR Intercom Interface is the
much-preferred choice.) Each interface
has a party-line active detection function
to ensure that should a beltpack or ac-
tive party-line circuit not be connected
the Model 45DC’s interface circuitry will
remain stable. This unique feature makes
certain that objectionable audio signals,
including oscillations and “squeals,” won’t
be sent to other Dante-enabled devices.

Model 45DC User Guide Issue 4, June 2020
Studio Technologies, Inc. Page 7
A signicant 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
independent 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 ve 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 rmware (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 receiver (input) and transmitter
(output) 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 ts into a
specic 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 dis-
tortion, 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 signicant
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 condi-
tions that are present on the connected
party-line cabling and user devices. When-
ever one of the Model 45DC’s auto null
buttons is pressed digital circuitry adjusts
the associated hybrid to achieve its maxi-
mum 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
nonvolatile memory.
Pro Audio Quality
The Model 45DC’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 headroom. Using passive
and active lters the frequency response
of the audio channels is limited to nomi-
nally 100 Hz to 8 kHz. This range was

Issue 4, June 2020 Model 45DC User Guide
Page 8 Studio Technologies, Inc.
selected to provide excellent performance
for human speech while maximizing the
ability of the hybrid circuits to create sub-
stantial “nulls.”
Audio Meters
The Model 45DC 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 channel. At the time of instal-
lation and setup the meters are invaluable
in helping to conrm correct operation.
During normal operation the meters offer
rapid conrmation of audio signals owing
in to and out of the unit. Additional LED
indicators are also provided on the front
panel, offering a status indication of the
party-line DC power sources, party-line
activity status, and the auto null functions.
Two other LEDs offer a direct indication
of which source is powering the Model
45DC.
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 45DC can detect call light
activity, convert it to a 20 kHz audio tone,
and transport the tone over the Dante
audio path. A Model 45DC unit at the “far
end” will detect the tone and re-generate
the call signal as a DC voltage on the au-
dio path. This allows full “end-to-end” call
light support between two or more Model
45DC units. It also allows a Model 45DC
to send and receive call light status with
an interconnected Model 45DR Dante to
2-Channel Party-Line Intercom Interface.
The Model 45DR is typically used with the
RTS TW-series of party-line user beltpacks
including the popular BP-325.
Ethernet Data, PoE, and DC
Power Source
The Model 45DC connects to a data net-
work using a standard 100 Mb/s twist-
ed-pair Ethernet interface. The physical
interconnection is made by way of a
Neutrik® etherCON RJ45 connector. While
compatible with standard RJ45 plugs,
etherCON allows a ruggedized, locking
interconnection for harsh or high-reliability
environments. The Model 45DC’s operating
power can be provided by way of the Eth-
ernet interface using the Power-over-Eth-
ernet (PoE) standard. This allows fast and
efcient interconnection with the associ-
ated data network. To support PoE power
management, the Model 45DC’s PoE inter-
face reports to the power sourcing equip-
ment (PSE) that it is a class 3 (mid power)
device. The unit can also be powered
using an external source of 12 volts DC.
For redundancy, both power sources can
be connected simultaneously. An internal
switch-mode power supply ensures that all
Model 45DC features, including party-line
intercom circuit power, are available when
the unit is powered by either source. Four
LEDs on the back panel display the status
of the network connection, Dante interface,
and PoE power source.
Simple Installation
The Model 45DC uses standard con-
nectors to allow fast and convenient
interconnections. An Ethernet signal is
connected using a Neutrik etherCON RJ45.
If Power-over-Ethernet (PoE) is available
operation will commence immediately.
An external 12 volt DC power source can
also be connected by way of a 4-pin XLR.
Party-line intercom connections are made

Model 45DC User Guide Issue 4, June 2020
Studio Technologies, Inc. Page 9
using two 3-pin male XLR connectors. The
Model 45DC is housed in a rugged yet
lightweight aluminum enclosure that is de-
signed to be “eld tough.” It can be used
as a standalone portable unit, supporting
what’s known in the broadcast world as
“throw-down” applications. Rack-mount
options are also available allowing one or
two units to be mounted in one space (1U)
of a standard 19-inch rack enclosure.
Future Capabilities and
Firmware Updating
The Model 45DC was designed so that its
capabilities can be enhanced in the future.
A USB connector, located on the Model
45DC’s back panel, allows the applica-
tion rmware (embedded software) to be
updated using a USB ash drive. To imple-
ment the Dante interface the Model 45DC
uses Audinate’s Ultimo™ integrated cir-
cuit. The rmware in this integrated circuit
can be updated via the Ethernet connec-
tion, helping to ensure that its capabilities
remain up to date.
Installation
In this section, signal interconnections will
be made using the connectors located on
the back panel of the Model 45DC. Con-
nections to one or more party-line user
devices or one or two existing party-line
intercom circuits will be made using the
3-pin XLR connectors. An Ethernet data
connection will be made using either a
standard RJ45 patch cable or an ether-
CON protected RJ45 plug. A 4-pin XLR
connector allows the connection of an
external source of 12 volts DC.
System Components
Included in the shipping carton are the
Model 45DC Intercom Interface and a user
guide. If a rack-mount front panel is going
to be used as part of the installation it will
typically be shipped in a separate carton.
If the installation or specic application
requires an external source of 12 volts DC
it needs to be provided separately. An ap-
plicable power supply, the Studio Technol-
ogies PS-DC-02, is available as an option.
Locating the Model 45DC
The location of the Model 45DC will de-
pend on the length of the cable runs
needed to link the unit with the associated
party-line intercom devices. This type of
circuit carries unbalanced audio which can
be susceptible to interference and cross-
talk issues. And since party-line intercom
circuits typically carry DC power a voltage
drop due to resistive loss can become an
issue. In general, minimizing the length
of the party-line intercom cables will help
ensure more reliable and consistent inter-
com system performance. Of equal impor-
tance is the 100-meter (325-foot) Ethernet
cable limitation. A nal location criterion is
to ensure that access to the Model 45DC’s
front panel is available. An optimal loca-
tion will allow convenient use of the auto
null pushbutton and easy observation of
the status and level meters LEDs.
Protecting the Enclosure
The Model 45DC is shipped as a self-con-
tained unit suitable for portable use or
placement in a semi-permanent location.
Installed on the bottom of the chassis
are screw-on “bump on” protectors (also
known as “rubber feet”). These are useful

Issue 4, June 2020 Model 45DC User Guide
Page 10 Studio Technologies, Inc.
if the unit is going to be placed on surfaces
where scratching of either the Model 45DC
or the surface material could take place.
The “feet” can be removed, without the use
of a tool, when rack- or custom-mounting
the unit.
Rack Mounting the
Model 45DC
For permanent or mobile applications it
might be desirable to mount one or two
Model 45DC units into one space (1U) of
a 19-inch rack enclosure. Two rack-mount
front panels, purchased separately, are
available from Studio Technologies. The
following provides details on how to install
and use the panels.
To attach a Model 45DC unit to the single-
unit rack-mount panel, begin the process
by using a 5/64-inch hex wrench to remove
the four 6-32 button-head machine screws
that hold the standard front panel to the
chassis. Note that the screws might be
quite tightly afxed. Ensure that a good-
quality hex wrench is used and press and
hold it rmly while turning counterclock-
wise. Unless this recommendation is fol-
lowed the wrench can “cam out” and the
head could be “stripped.”
Using the screws that were just removed,
attach the rack-adapter front panel to the
Model 45DC’s chassis. To prevent damage
care is required when aligning the front
panel with the LEDs and auto null push-
button switch that protrude through both
the Model 45DC’s chassis and front panel.
Tighten the four screws only after a careful
inspection ensures that the switch and all
28 of the LEDs protrude through the front
panel without interference. To allow vertical
clearance in the associated rack, remove
the four “bump on” protectors from the
bottom of the chassis. They are removed
by using the ngers to rotate them counter-
clockwise; no tool is required. Carefully
protect and store the standard front panel,
along with the “bump on” protectors, for
possible later use.
Mounting a Model 45DC to a dual-unit
rack-mount panel follows the same proce-
dure but will apply to two units. Store both
of the removed standard front panels and
the eight “bump on” protectors for possi-
ble later use. Note that on the rack-panels
graphics the unit on the left is designated
as A while the unit on the right is desig-
nated as B. This is provided so that each
can be easily identied during installation,
troubleshooting, and operation.
Once the desired one or two Model 45DC
units have been installed in a rack-mount
front panel, the assembly can be mounted
into the designated equipment rack. One
space (“1U” or 1.75 vertical inches) in
a standard 19-inch equipment rack is
required. Secure the front panel into
the equipment rack using two mounting
screws per side.
Ethernet Connection
An Ethernet connection that supports
100BASE-TX (100 Mb/s over twisted-pair)
is required for the Model 45DC’s Dante
Audio-over-Ethernet connectivity. A
10BASE-T connection is not sufcient for
Model 45DC operation. A 1000BASE-T
(“GigE”) connection is not supported
unless it can automatically “fall back” to
100BASE-TX operation. An Ethernet con-
nection that supports Power-over-Ethernet
(PoE) is preferred as it will provide operat-
ing power for the Model 45DC. To support
PoE switch (PSE) power management the
Model 45DC will enumerate itself as a PoE

Model 45DC User Guide Issue 4, June 2020
Studio Technologies, Inc. Page 11
class 3 device. If PoE is not available an
external 12 volt DC power source can be
connected. This will be discussed in the
next section of this guide.
The 100BASE-TX Ethernet connection is
made by way of a Neutrik etherCON pro-
tected RJ45 connector that is located on
the back panel of the Model 45DC. This
allows connection by way of a cable-
mounted etherCON plug or a standard
RJ45 plug. The Model 45DC’s Ethernet
interface supports auto MDI/MDI-X so
that most cabling implementations will
be directly supported.
External 12 Volt DC Input
An external source of 12 volts DC can be
connected to the Model 45DC by way of a
4-pin male XLR connector which is located
on the back panel. While the requirement
for the external source is to be nominally
12 volts, correct operation will take place
over a 10 to 18 volt range. The Model 45DC
requires 1.0 amperes maximum for cor-
rect operation. The DC source should be
terminated to a 4-pin female XLR connector
with pin 1 negative (–) and pin 4 positive
(+). Purchased as an option, the PS-DC-02
power supply is available from Studio Tech-
nologies. Its AC mains input allows connec-
tion to 100-240 volts, 50/60 Hz and its
12 volt DC, 1.5 amperes maximum output
is terminated on a 4-pin female connector.
As previously discussed in this guide, an
Ethernet connection that provides Pow-
er-over-Ethernet (PoE) can serve as the
Model 45DC’s power source. Alternately,
an external 12 volt DC source can be con-
nected. For redundancy, both PoE and the
external 12 volt DC source can be connect-
ed at the same time. If both PoE and an
external 12 volt DC source are connected,
power will be drawn only from the PoE
supply. If the PoE source becomes inoper-
ative the 12 volt DC source will provide the
Model 45DC’s power with no interruption
in operation. (Of course, if both PoE and
Ethernet data support are lost that is a very
different situation!)
Party-Line Intercom
Connections
The Model 45DC’s party-line intercom inter-
face is designed to function in two distinct
ways. It can be connected to one or two
“powered” broadcast-standard 2-channel
party-line intercom circuits or directly to
one or two sets of party-line intercom user
devices. A single-channel party-line inter-
com circuit, such as frequently associated
with equipment from Clear-Com, has DC
power and one audio channel on a 3-pin
XLR connector. The connector is wired
such that common is on pin 1, 22 to 30
volts DC is on pin 2, and audio is on pin 3.
An impedance-generating network pro-
vides a 200 ohm audio load from pin 3 to
pin 1. When the Model 45DC’s party-line in-
terfaces are connected to existing intercom
circuits they act, from an audio standpoint,
as standard user devices. They don’t draw
(nor supply) any DC power.
The Model 45DC’s two party-line interfaces
can serve to create two “mini” intercom
circuits. They each provide a 28 volt DC
intercom power source and a 200 ohm
impedance generator, allowing a limited
number of single-channel intercom user
devices to be directly connected. The Mod-
el 45DC’s two internal 28 volt DC power
sources each have a maximum current of
150 mA. This modest amount of power can
be very useful but requires that the type
and number of connected user devices be

Issue 4, June 2020 Model 45DC User Guide
Page 12 Studio Technologies, Inc.
selected appropriately. Many entertainment
applications use the legacy Clear-Com
RS-501 beltpack and each Model 45DC
intercom circuit can directly support up to
three of them. With the newer and more
energy efcient Clear-Com RS-701 it should
be possible to connect up to ve of them.
Wiring from the Model 45DC intercom in-
terface’s 3-pin male XLR connectors to the
user devices requires that a 1-to-1, 2-to-2,
3-to-3 wiring scheme on the mating 3-pin
XLR connectors be maintained.
Compatibility with 2-Channel
Intercom Systems
As previously discussed in this guide, the
Model 45DC is designed to support sin-
gle-channel party-line intercom circuits and
user devices. It’s possible that applications
that involve 2-channel party-line intercom
circuits and user devices (typically associ-
ated with the RTS TW-series of products)
can also be supported. These circuits and
devices typically utilize common on pin 1,
28 to 32 volts DC and channel 1 audio on
pin 2, and channel 2 audio on pin 3. When
connected to a Model 45DC only channel
2 will be active; channel 1 would not be
utilized. A better means to support these
2-channel circuits and devices is to use the
Studio Technologies Model 45DR Interface.
This unit, the “cousin” of the Model 45DC,
is optimized for 2-channel party-line inter-
com applications. Rather than providing
two single-channel interfaces the Model
45DR provides one 2-channel interface.
Detailed information about the Model 45DR
is available on the Studio Technologies
website (studio-tech.com).
Conguration
Back-Panel DIP Switches
A 4-position DIP switch assembly, labeled
Conguration, is located on the Model
45DC’s back panel. Switch SW1 allows
the Model 45DC’s call light support func-
tion to be disabled. Switch SW2 allows the
party-line active detection function to be
disabled. Switches SW3-4 are not current-
ly utilized and have no impact on Model
45DC operation.
Call Light Support
Switch SW1 allows the call light support
function to be disabled. When switch SW1
is in its off (down) position the call light
support function is enabled. When SW1
is in its on (up) position the function is
disabled. For most applications the call
light support function should remain en-
abled. Only special circumstances would
merit disabling the function. Note that the
call light function between user devices
connected to the same Model 45DC inter-
face will always be active. Disabling the
Model 45DC’s call light support function
only impacts the call function that’s sent
and received by way of the Dante audio
connections.
Figure 3. Call light support conguration switch

Model 45DC User Guide Issue 4, June 2020
Studio Technologies, Inc. Page 13
Party-Line Active Detection
Function
When local power has been selected for
a Model 45DC party-line interface and
switch SW2 is in its off (down) position a
minimum of approximately 5 mA of current
must be drawn from that interface for an
“active” condition to be recognized. When
this condition is met the associated active
LED on the front panel will light and the
Dante output audio path will be active. This
default setting is appropriate for most ap-
plications and helps to maintain the most
stable audio performance.
Switch SW2 allows the party-line active
detection function to be disabled. When
SW2 is in its on (up) position no minimum
party-line current draw is required for the
active LED to be lit and an output audio
path to be active. Only in special situations
would the function need to be disabled.
One example is the case where a Model
45DC is being used with a Telex®BTR-700
Wireless Intercom System. The BTR-700 is
designed to directly interface with a par-
ty-line intercom circuit. This circuit would
typically have DC power and one audio
channel that has a terminating impedance
of nominally 200 ohms. The Model 45DC
can provide two such circuits when the
local power functions are enabled. But a
problem arises as the BTR-700 does not
draw current from the connected inter-
com circuit. It doesn’t function in the same
manner as would a typical beltpack, in-
stead using an external source of power
for operation. So in this case, the Model
45DC’s party-line interface would not
supply current, the active LED would not
light, and the output audio path would not
be enabled. Users of the BTR-700 would
be able to hear Model 45DC input audio
but not send audio out the Dante interface.
Disabling the party-line active detection
function by placing SW2 to its on (up) posi-
tion would resolve this issue. Even though
no DC current would be supplied by the
Model 45DC successful operation would
take place.
When the Model 45DC has been set to
not provide local power the party-line
active detection function works in a slightly
different way. Only if a DC voltage of ap-
proximately 18 or greater is present on
pin 2 will the party-line interface recognize
that a valid interconnection is present. In
this case, the active LED will light and the
Dante output audio path will be active.
When SW2 is in its on (up) position the
party-line active detection function will be
disabled and monitoring of DC voltage on
pin 2 will not take place. In this situation,
the active LED will always be lit and the
output audio path will be active. As of the
writing of this guide the practical applica-
tion of this specic conguration has not
been determined. But it’s ready should the
need arise!
Dante Conguration
To integrate the Model 45DC into an appli-
cation a number of Dante-related parame-
ters can be congured. At a minimum, the
Figure 4. Party-line active detection function
conguration switch

Issue 4, June 2020 Model 45DC User Guide
Page 14 Studio Technologies, Inc.
audio receiver (input) and audio transmitter
(output) channels must be routed. The con-
guration settings will be stored in non-
volatile memory within the Model 45DC’s
circuitry. The Model 45DC uses the Ultimo
2-input/2-output integrated circuit to imple-
ment the Dante architecture. This dictates
which parameters can be congured and
what choices are available.
The audio receiver (input) and transmit-
ter (output) channels associated with the
Model 45DC’s Dante interface must be
assigned to desired sources and destina-
tions. This will typically be done with the
Dante Controller software application which
is available for download free of charge
at audinate.com. Versions are available to
support Windows® and OS X®operating
systems. Within Dante Controller a “sub-
scription” is the term used for routing a
transmitter ow (a group of output chan-
nels) to a receiver ow (a group of input
channels). Note that as of the writing of this
guide the Ultimo integrated circuit limits
the number of Dante ows to two in each
direction (two transmitter and two receiver).
These can either be unicast, multicast, or
a combination of the two.
The Model 45DC has a default Dante
device name of ST-M45DC followed by
a unique sufx. The sufx identies the
specic Model 45DC that is being cong-
ured; it relates to the MAC address of the
unit’s Ultimo integrated circuit. The Model
45DC provides two Dante transmitter (out-
put) channels with the default names
of From PL Ch A and From PL Ch B.
The Model 45DC has two Dante receiver
(input) channels with default names of
To PL Ch A and To PL Ch B. Using Dante
Controller these names can be revised as
appropriate for the specic application.
The Model 45DC only supports an audio
sample rate of 48 kHz with no pull-up/pull-
down values available. This value can be
selected using the Dante Controller appli-
cation. The Model 45DC can serve as the
clock master for a Dante network but in
most cases that would not be optimal.
Model 45DC units will typically be used in
either of two congurations: “point-to-point”
or in association with other Dante-enabled
equipment. The rst conguration nds
two units working together to “link” two
physical locations. At each location there
will either be one or two existing party-line
intercom circuits or one or two sets of user
devices. The two Model 45DC units will be
operating “point-to-point,” interconnected
by way of the associated Ethernet network.
For this application the audio routing would
be very simple. To PL Ch A on each unit
would be routed to From PL Ch A on the
other unit. And To PL Ch B on each unit
would be routed to From PL Ch B on the
other unit.
The other typical applications will have one
Model 45DC connected to one or two exist-
ing party-line intercom circuits or support-
ing one or two sets of user devices. The
unit’s audio channels would be routed to
input and output audio channels on associ-
ated Dante-enabled equipment. For exam-
ple, the RTS ADAM matrix intercom system
provides Dante interconnection capability
using its OMNEO interface card. The au-
dio channels on the Model 45DC would
be routed to and from audio channels on
the OMNEO card. Other equipment that
supports Dante, such as audio consoles
or audio interfaces (Dante-to-MADI, Dante-
to-SDI, etc.), can have their audio channels
routed to and from a Model 45DC.

Model 45DC User Guide Issue 4, June 2020
Studio Technologies, Inc. Page 15
Operation
At this point the Model 45DC should have
its party-line and Ethernet connections
made. Depending on the application an
external 12 volt DC power connection may
have also been made. The Dante receiver
(input) and transmitter (output) channels
should have been routed using the Dante
Controller software application. Normal op-
eration of the Model 45DC can now begin.
Initial Operation
The Model 45DC will begin functioning a
few seconds after its power source is con-
nected. As previously discussed, the power
source can be provided by Power-over-
Ethernet (PoE) or an external source of
12 volts DC. If both are connected the PoE
source will power the unit. Should PoE sub-
sequently no longer be available, operation
will continue using the external source.
Upon Model 45DC power up many of
the status and meter LEDs will activate in
test sequences. The PoE and USB LEDs,
located on the back panel, will light one
after another. On the front panel the input
power, channel status and level meters
LEDs will light in a sequence. Once the test
sequences have completed two columns
of front-panel level meter LEDs will mo-
mentarily display the version number of the
unit’s application rmware. Details on how
to “read” the version number is provided in
the Technical Notes section of this guide.
The Model 45DC will now begin normal
operation. The way in which the LINK/ACT,
SYS, SYNC, and PoE LEDs (all located on
the back panel below the etherCON con-
nector) light will depend on characteristics
related to the connected Ethernet signal
and the conguration of the unit’s Dante
interface. Details will be covered in the next
paragraph. The user is presented on the
front panel with two pushbutton switch, two
input power status LEDs, six channel status
LEDs, and four 5-segment LED level me-
ters. These resources are simple to operate
and understand, as will be described in
later paragraphs.
Ethernet, PoE, and Dante
Status LEDs
Four status LEDs are located below the
etherCON connector on the Model 45DC’s
back panel. The LINK/ACT LED will light
green whenever an active connection to
a 100 Mb/s Ethernet network has been
established. It will ash on and off in re-
sponse to data packet activity. The PoE
LED will light green whenever Power-
over-Ethernet (PoE) associated with the
connected Ethernet signal is providing
operating power for the Model 45DC. The
SYS and SYNC LEDs display the operating
status of the Dante interface and associ-
ated network. The SYS LED will light red
upon Model 45DC power up to indicate
that the Dante interface is not ready. After
a short interval it will light green to indicate
that it is ready to pass data with another
Dante device. The SYNC LED will light red
when the Model 45DC is not synchronized
with a Dante network. It will light solid
green when the Model 45DC is synchro-
nized with a Dante network and an external
clock source (timing reference) is being re-
ceived. It will slowly light on and off green
when the Model 45DC is part of a Dante
network and is serving as a clock master.

Issue 4, June 2020 Model 45DC User Guide
Page 16 Studio Technologies, Inc.
How to Identify a Specic
Model 45DC
The Dante Controller software application
offers an identify command that can be
used to help locate a specic Model 45DC.
When identify is selected for a specic unit
its meter LEDs will light in a unique pattern.
In addition, the SYS and SYNC LEDs, locat-
ed directly below the etherCON connector
on the back panel, will slowly ash green.
After a few seconds the LED identication
patterns will cease and normal Model 45DC
level meter and Dante status LED operation
will again take place.
Level Meters
The Model 45DC contains four 5-segment
LED level meters. These meters are pro-
vided as a support aid during installation,
conguration, operation, and troubleshoot-
ing. The meters represent the strength of
the audio signals going to and coming
from the two party-line intercom interfaces.
General
Each interface has two meters associated
with it, one represents audio being sent to
the party-line circuit and the other repre-
senting audio coming from the party-line
circuit. The meters are calibrated to reect
the level in dB relative to the reference
(nominal) level of the party-line circuit. In
the case of the Model 45DC the nominal
level of the party-line was selected to be
–14 dBu since that matches that of the typi-
cal single-channel party-line circuit. (Very
early single-channel Clear-Com systems
had a nominal level of –20 dBu but that’s
no longer true for contemporary units.)
As an example of how the meters function
let’s review the situation where the channel
A TO meter has its bottom three LEDs
(–18, –12, and –6) lit solid and its 0 LED
just barely lighting. This would indicate
that a signal with an approximate level of
–14 dBu is being sent to the associated
party-line intercom circuit. (Also note that
this –14 dBu signal on the party-line in-
tercom circuit will translate to a –20 dBFS
digital audio signal on the Dante interface.
This is due to Studio Technologies select-
ing –20 dBFS as the reference (nominal)
level for Dante.)
Each level meter contains four green LEDs
and one yellow LED. The four green LEDs
indicate party-line circuit signal levels at or
below –14 dBu. The top LED is yellow and
indicates a signal that is 6 dB or greater
than the –14 dBu nominal level. An audio
signal that causes the yellow LED to light
doesn’t necessarily indicate an excessive
level condition, but it does provide a warn-
ing that at some stage reducing the signal
level may be prudent. Typical operation
with normal signal levels should nd the
meters lighting near their 0 point. Signal
peaks may cause the yellow LEDs to ash.
But a yellow LED that lights fully during
normal operation will typically indicate ex-
cessive signal level and/or a conguration
problem with associated Dante-enabled
equipment.
Non-Optimal Signal Levels
If the meters consistently display levels that
are lower or higher than the 0 (reference)
point it’s possible that a conguration issue
exists. This would typically be related to
incorrect settings on the equipment con-
nected to the associated Dante input and
output channels. (This situation is almost
impossible to occur if two Model 45DC
units were congured “point-to-point” as
no Dante digital audio level adjustment is
provided.) With a digital matrix intercom

Model 45DC User Guide Issue 4, June 2020
Studio Technologies, Inc. Page 17
system this problem could be due to an
incorrect conguration having been made
to a specic channel or port. For example,
the RTS ADAM system has a published
nominal level of +8 dBu, but it’s not clear
how this translates into a digital audio level
on an associated Dante channel. Using its
conguration software it’s most likely pos-
sible to set the nominal level of intercom
key panels or ports to something different
than +8 dBu. The best solution in this case
would be to adjust the associated OMNEO
(Dante-compatible) port such that it results
in a nominal level of –20 dBFS on the as-
sociated Dante channels. This should lead
to the best performance of the Model 45DC
and associated party-line user devices.
Audio Levels and Party-Line Termination
The FROM meters display the level of sig-
nals that come from the party-line circuit.
These signals are then sent as digital audio
to the associated Dante output channels.
An issue may arise if the signals coming
from the connected party-line circuit or user
devices aren’t at a sufcient level so that a
normal meter display level can be reached.
For a party-line circuit to function correctly
the impedance (resistance to AC signals
such as audio) must be approximately 200
ohms. Typically to achieve this depends
on a single piece of equipment providing
a single audio termination. This termina-
tion, 200 ohms nominally, is almost always
made at the power supply source. But it’s
possible that another device, such as a
second active power supply on the same
party-line circuit, will cause a “double-
termination” condition. This will result in
a 100 ohm party-line circuit impedance and
an audio level drop of about 6 dB. Remov-
ing the unwanted termination is the only
valid means of correcting the problem.
In most cases this will be simple to solve.
It’s easily possible for the Model 45DC’s
local power source, which also provides
200 ohm termination networks for the
audio channel, to be enabled when the
Model 45DC is connected to an externally-
powered party-line circuit. This would
be incorrect, leading to the “double-
termination” condition. Turning off the
Model 45DC’s local power source by
pressing and holding the auto null button
is all that is required.
Power Status LEDs
Two green LEDs are located on the front
panel and are associated with operating
power. The PoE LED indicator will light
whenever an Ethernet connection with
Power-over-Ethernet (PoE) capability is
connected. The DC power LED will light
whenever an external DC voltage has
been applied. The acceptable range is
10 to 18 volts DC. If both power sources
are present the PoE source will provide
the Model 45DC’s operating power.
Party-Line Operating Mode
Selection
As discussed previously in this guide, the
Model 45DC provides two main operating
modes. One mode is used when a Model
45DC channel is required to create a par-
ty-line circuit, providing 28 volts DC and
a 200 ohm termination impedance. In this
mode, user devices such as beltpacks can
be directly supported. When this mode is
selected the local power status LED will
be lit. The second mode allows the Mod-
el 45DC to be connected to an existing
powered party-line intercom circuit. In
this mode, the local power status LED will
not be lit. To select the desired operating

Issue 4, June 2020 Model 45DC User Guide
Page 18 Studio Technologies, Inc.
mode is simple, only requiring the audio
null pushbutton switch of the desired in-
terface channel to be pressed and held for
two seconds. The mode will change and
the local power LED will display accord-
ingly. The button can then be released.
The selected operating mode for each
interface channel will be stored in nonvola-
tile memory so that they will restore after a
power-down/power-up cycle.
Local Power Mode Operation
When a channel’s local power LED is lit
the Model 45DC provides party-line power
and a 200 ohm termination impedances
to create a single-channel party-line cir-
cuit. The party-line interface supplies 28
volts DC on pin 2 of the 3-pin XLR connec-
tors. A maximum current draw of 150 mA
per interface is available. This current is
sufcient to power intercom user devices
such as beltpacks. A common entertain-
ment or corporate application might use
Clear-Com RS-501 or RS-701 beltpacks.
Select the connected devices so that their
total maximum current doesn’t exceed
150 mA. That’s not always the easiest g-
ure to calculate but a web search will gen-
erally nd specications for all commonly
used devices. For example, a search nds
that the ubiquitous RS-501 will consume a
maximum of 50 mA of current. According
to this gure up to three of these units can
be connected to a Model 45DC. A newer
version, the RS-701 has a quiescent cur-
rent draw of 12 mA and an approximate
maximum of 23 mA. From this information
one could estimate that up to ve of these
units can easily be supported.
The active LED will light when a minimal
amount of current is owing from the Mod-
el 45DC intercom interface to the connect-
ed user device or devices. This current,
approximately 5 mA, provides a “circuit-
active” signal to the Model 45DC’s rm-
ware, indicating that normal operation
is taking place. This helps to prevent un-
wanted audio signals from passing to the
Dante audio channels when no party-line
devices are connected.
The Model 45DC’s two party-line intercom
power supply circuits operate indepen-
dently under rmware control. This allows
detection of fault conditions and protection
of the Model 45DC’s circuitry. Upon initial
Model 45DC party-line intercom power up
no monitoring of the intercom power out-
puts takes place for three seconds. This
allows the Model 45DC’s circuitry and the
connected intercom user devices to sta-
bilize. The active LEDs, which monitor the
DC voltage on pin 2 of the 3-pin XLR con-
nectors associated with the intercom chan-
nels, will light to indicate that an output is
active. After this initial delay period moni-
toring becomes active. A fault condition is
detected if the voltage on pin 2 falls below
24 for a continuous 1-second interval. The
hardware and rmware responds to this
condition by turning off the associated
power source to pin 2 and ashing the
active LED as a warning. After a 5-second
“cool-down” interval the output returns to
the same condition as upon initial power
up. Power is again applied to pin 2, the
active LED will light, and monitoring won’t
begin for another three seconds. A full
short-circuit condition applied to either of
the Model 45DC’s party-line circuits will
result in a continuous cycle of four seconds
on (three seconds for start up and one
second for detection) and ve seconds
off on that specic circuit.

Model 45DC User Guide Issue 4, June 2020
Studio Technologies, Inc. Page 19
External Party-Line Circuit
Operation
When an interface channel’s local power
LED is not lit that interface is intended to be
connected to an external party-line circuit.
The external circuit must provide power
and termination impedances to “create”
the party-line, with the Model 45DC simply
serving as a user device. When connected
to an external party-line circuit the active
LED associated with that interface channel
will light when the voltage on pin 2 is equal
to or greater than approximately 18. If this
condition is present then normal Model
45DC operation will be able to take place.
Auto Null
The Model 45DC contains circuitry to auto-
matically null the hybrid networks associ-
ated with the two party-line interfaces.
This procedure minimizes the mixing of the
audio signals being received by and sent
to each party-line interface circuit. Normally
the nulling processes are performed at the
time of initial Model 45DC conguration but
there’s no reason why either or both can’t
be initiated any time one desires. The only
time that an auto null must be performed is
if conditions have changed with the party-
line user devices and wiring connected to
a Model 45DC’s party-line connector. Even
a small change to a party-line intercom cir-
cuit, such as adding or removing a section
of cable, is often enough to require that the
auto null process be performed.
Two pushbutton switches are provided
to activate the auto null process for each
interface. To initiate auto null rst requires
that an interface’s active LED be lit. When
an interface’s operating mode is set for
local power the active LED will light when
current is owing from the internal power
supply. When the local power LED is not lit
the active LED must be lit, indicating that
sufcient DC voltage is present on pin 2
of the connected party-line circuit. Once the
active LED is lit initiating an auto null func-
tion only requires pressing and releasing
(“tapping”) the appropriate auto null but-
ton. An LED provides a visual indication of
the status of the auto null process, ashing
when the auto null process is active. If the
auto null button is pressed when its as-
sociated active LED is not lit the auto null
process will not start. The auto null LED
will quickly ash on and off a few times to
indicate this condition. Only one auto null
process can be active at any one time.
Nothing will happen if either auto null but-
ton is pressed when the auto null process is
active for an interface. (An interface’s mode
can be changed when the auto null is active
on the other interface.)
An auto null sequence begins in this man-
ner: If local power is being provided to the
party-line interface by the Model 45DC it will
momentarily turn off and then turn on again.
This will act as a “mic kill” signal, ensuring
that microphones associated with the con-
nected user devices will be placed in their
off state. Then the audio input and output
signal paths associated with the Dante
input and output channels will mute. Next a
series of tones will be sent to the party-line
interface’s audio path. Other Model 45DC
circuitry, under rmware control, will rapidly
perform adjustments to achieve the best
null possible. After the adjustments have
been made the results are stored in nonvol-
atile memory. Once the process is complete
the Dante audio input and output paths are
again activated.
If possible, prior to performing an auto
null it’s polite to warn all personnel who

Issue 4, June 2020 Model 45DC User Guide
Page 20 Studio Technologies, Inc.
are actively using connected party-line
intercom devices. The tones sent to the
party-line circuit during the nulling process
are not excessively loud or obnoxious,
but most users might want to remove their
headsets during the process. In addition
to warning users, it’s a good idea to ask
them to mute any active microphones.
Muting the microphones can be signicant
as obtaining a “deep” null requires that
no extraneous signals be present on the
intercom circuit. As previously discussed,
if the Model 45DC is supplying local inter-
com power the microphones will automat-
ically be muted. But for applications that
connect to an existing party-line intercom
circuit the user’s must manually mute the
microphones.
The Model 45DC provides a call light
support function, allowing call light sig-
nals associated with user devices on two
Model 45DC interfaces to work together.
The function also allows a Model 45DC
interconnected with a Model 45DR Dante
to 2-Channel Party-Line Intercom Inter-
face to have common call light activity. No
operator action is required for the call light
support function to perform its task. How-
ever, placing DIP switch SW1, located on
the back panel, to its on (up) position will
disable the function.
USB Interface
A USB type A connector and associated
status LED is located on the back panel
of the Model 45DC. This data interface is
used only for updating the unit’s applica-
tion rmware. No audio data of any kind
will pass through it. For details please
refer to the Technical Notes section of
this guide.
Technical Notes
Call Light Support
A “call” or “call light” indication on a
Clear-Com party-line intercom circuit is
transmitted by way of a DC voltage that is
applied to the audio path, which is typi-
cally pin 3 of the interconnecting cable.
This DC voltage is summed (added) to
any audio that is present. The Model 45DC
detects when a call light signal is active by
monitoring the audio path for the presence
of a DC voltage. A signal of approximately
5 Vdc or greater is needed to indicate that
the call function is active. The Model 45DC
can also generate a call signal by applying
a DC voltage to audio path. The DC, ap-
proximately 16 V, is ramped up and down
to minimize the addition of clicks or pops
to the audio signal.
While the Model 45DC can detect and
generate a call signal, it’s not possible to
directly send and receive these DC signals
over a Dante interconnection that’s intend-
ed only for audio transport. The Model
45DC works around this issue by convert-
ing the DC call light signaling to one that’s
based on a 20 kHz audio tone. An astute
user will recognize this as the call method
used by the TW-series from RTS; instead
of signaling via DC in the audio path a
20 kHz signal is used. In the “telco” world
this would be referred to as in-band sig-
naling, not dissimilar to the touch-tone
dialing method that’s used on analog
telephone lines. But unlike touch-tone
signals, a 20 kHz signal has the advantage
of being above the hearing range of most
humans. This allows normal intercom
audio and a 20 kHz call signal to be ac-
tive simultaneously. And transporting this
combined talk/call signal over the Model