Studio Technologies 374A User manual

Copyright © 2018 by Studio Technologies, Inc., all rights reserved
www.studio-tech.com
50658-0618, Issue 1
User Guide
Issue 1, June 2018
This User Guide is applicable for serial numbers
M374A-02501 and later with application firmware 1.1 and later
and Dante® firmware 1.0.0 (UltimoX4 4.1.2.1) and later
Model 374A Intercom Beltpack

This page intentionally left blank.

Model 374A User Guide Issue 1, June 2018
Studio Technologies, Inc. Page 3
MODEL 374A
INTERCOM BELTPACK
Table of Contents
Revision History ............................................................ 4
Introduction ................................................................... 5
Getting Started .............................................................. 7
Operation ...................................................................... 13
Technical Notes ............................................................. 16
Specifications ................................................................ 21

Issue 1, June 2018 Model 374A User Guide
Page 4 Studio Technologies, Inc.
MODEL 374A
INTERCOM BELTPACK
Revision History
Issue 1, June 2018:
1. Initial release.

Model 374A User Guide Issue 1, June 2018
Studio Technologies, Inc. Page 5
MODEL 374A
INTERCOM BELTPACK
Introduction
The Model 374A Intercom Beltpack
begins with the features offered by tradi-
tional party-line intercom user devices and
adds a range of new capabilities along
with the advanced performance and flex-
ibility that Dante® audio-over-Ethernet
provides. With four independent talk and
listen channels the Model 374A bridges
the gap between typical single- and dual-
channel party-line devices and permanent-
ly installed multi-channel intercom panels.
Imagine the possibilities—four channels
of high-quality party-line intercom in a
compact, user-worn package.
Over a standard IP network, multiple
Model 374A units can be used in party-
line (PL) intercom applications with help
from an external Dante-enabled audio
matrix such as the Studio Technologies
Model 5422 Dante Intercom Audio Engine.
Or, units can be used “point-to-point” or
interfaced with Dante-compatible matrix
intercom systems.
Only a single Power-over-Ethernet (PoE)
connection is required for operation. Key
user features can be easily configured us-
ing the STcontroller software application.
Configurable parameters include electret
microphone powering, microphone pre-
amplifier gain, talk button operation, and
headphone channel assignment. User
features include integrated sidetone,
remote mic kill (“talk off”), and monitor-
only modes. The wide range of capabilities,
along with the excellent audio quality pro-
vided by the digital audio signal path, offers
a unique and powerful user experience.
Set up and configuration of the Model 374A
is simple. An etherCON® RJ45 receptacle
is used to interconnect with a standard
twisted-pair Ethernet port associated with
a local-area network (LAN). This connec-
tion provides both power and bidirectional
digital audio. A broadcast or intercom-style
stereo or monaural headset with a dynamic
or electret (DC-powered) microphone
interfaces with the unit using a 5-pin XLR
connector.
The STcontroller software application is
used to select the unit’s operating param-
eters. Four talk pushbutton switches can
be configured for optimal operation. Four
push-in/push-out (“pop out”) rotary con-
trols make it easy to set and maintain the
desired headphone output level. The Mod-
el 374A’s enclosure is made from an alu-
minum alloy which offers both light weight
and ruggedness. A stainless steel “belt
clip,” located on the back of the unit, allows
direct attachment to a user’s clothing.
Figure 1. Model 374A Intercom Beltpack top and bottom views

Issue 1, June 2018 Model 374A User Guide
Page 6 Studio Technologies, Inc.
MODEL 374A
INTERCOM BELTPACK
The audio quality of the Model 374A’s four
audio channels is excellent, with low distor-
tion, low noise, and high headroom. Care-
ful circuit design and rugged components
ensure long, reliable operation. A wide
range of applications can be supported,
including sports and entertainment TV and
radio events, streaming broadcasts, corpo-
rate and government AV installations, and
post-production facilities.
Dante Audio-over-Ethernet
Audio data is sent to and received from the
Model 374A using the Dante audio-over-
Ethernet media networking technology.
As a Dante-compliant device, the Model
374A’s four audio output (Dante transmit-
ter) and four audio input (Dante receiver)
channels can be interconnected (routed)
with other devices using the Dante Control-
ler software application. The Dante trans-
mitter and receiver channels are limited to
supporting four Dante flows, two in each
direction. The digital audio’s bit depth is up
to 24 with a sampling rate of 48 kHz. The
Model 374A is AES67 compatible and com-
pliant with the Dante Domain Manager™
software application.
Two bi-color LEDs provide an indication
of the Dante connection status. The Dante
Controller’s Identify command takes on a
unique role with the Model 374A. Not only
will it cause the talk button LEDs to light
in a unique highly visible sequence, it can
also be configured to turn off any active
talk channels.
Audio Quality
The Model 374A’s completely “pro”
performance is counter to the less-than-
stellar reputation of typical party-line
(PL) intercom audio. A low-noise, wide
dynamic-range microphone preamplifier
and associated voltage-controlled-amplifier
(VCA) dynamics controller (compressor)
ensures that microphone audio quality is
preserved while minimizing the chance of
signal overload. DC power to support elec-
tret microphones can be enabled if neces-
sary. The output of the microphone preamp
and compressor is routed to an analog-to-
digital converter (ADC) section that sup-
ports a sampling rate of 48 kHz with a bit
depth of up to 24. The audio signal, now
in the digital domain, travels through the
processor and on to the Dante interface
section where it is packetized and prepared
for transport over Ethernet.
Audio input signals arrive via four Dante
receiver channels. The supported sam-
pling rate is 48 kHz with a bit depth of up to
24. The audio signals pass into the Model
374A’s processor where channel routing,
headphone level control, and sidetone
creation are performed within the digital
domain. This provides flexibility, allowing
for precise control of the audio signals and
eliminates the need for the four rotary level
controls from having to directly handle
analog audio signals. The audio signals
destined for the 2-channel headphone out-
put are sent to a high-performance digital-
to-analog converter and then on to robust
driver circuitry. High signal levels can be
provided to a variety of headsets, head-
phones, and earpieces.
Configuration Flexibility
A highlight of the Model 374A is its ability to
be easily configured to meet the needs of
specific users and applications. All
configuration choices are made using
the STcontroller software application that
communicates with the Model 374A by way
of an Ethernet network connection. Con-
figurable parameters include microphone

Model 374A User Guide Issue 1, June 2018
Studio Technologies, Inc. Page 7
MODEL 374A
INTERCOM BELTPACK
power and preamplifier gain, sidetone au-
dio operationl, talk button operation, and
headphone monitoring.
The microphone input can be selected for
compatibility with dynamic or electret (DC-
powered) microphones. The gain of the
microphone preamplifier can be selected
from among four choices, two for sup-
porting dynamic microphones and two for
supporting electret microphones. These
choices allow compatibility with a variety
of microphones that are part of broadcast
and intercom headsets.
A unique Model 374A feature is the ability
to individually configure the way in which
the four talk pushbutton switches function;
four choices are available. For standard
intercom beltpack operation either Push
to Talk or Push to Talk/Tap to Latch opera-
tion can be selected. For situations where
only monitoring of an intercom channel
is desired a Talk Disabled mode is avail-
able. And for advanced monitoring-only
situations the Talk Disabled/Phones Tap to
Latch mode can be selected such that a
button will serve in an audio on/off role.
Four audio channels arrive via Dante and
are destined for the 2-channel headphone
output. Each input source can be inde-
pendently routed to the left headphone
channel, right headphone channel, or both
the left and right headphone channels.
This flexibility allows a variety of listening
environments to be created, including
stereo, single-channel monaural, and
dual-channel monaural.
Ethernet Data and PoE
The Model 374A connects to an Ethernet
data network using a standard 100 Mb/s
twisted-pair Ethernet interface. The physi-
cal interconnection is made by way of
a Neutrik® etherCON RJ45 receptacle.
While compatible with standard RJ45
plugs, etherCON allows a ruggedized and
locking interconnection for harsh or high-
reliability environments. An LED displays
the status of the network connection.
The Model 374A’s operating power is
provided by way of the Ethernet interface
using the 802.3af Power-over-Ethernet
(PoE) standard. This allows fast and
efficient interconnection with the associ-
ated data network. To support PoE power
management, the Model 374A’s PoE
interface reports to the power sourcing
equipment (PSE) that it’s a class 1 (very
low power) device.
Future Capabilities and
Firmware Updating
The Model 374A was designed such that
its capabilities and performance can be
enhanced in the future. A USB connector,
located on the unit’s main circuit board
(underneath the unit’s cover), allows the
application firmware (embedded software)
to be updated using a USB flash drive.
The Model 374A uses Audinate’s Ultimo™
integrated circuit to implement the Dante
interface. The firmware in this integrated
circuit can be updated via the Ethernet
connection, helping to ensure that its
capabilities remain up to date.
Getting Started
What’s Included
Included in the shipping carton are a
Model 374A Intercom Beltpack and a
printed copy of this guide. As a device that
is Power-over-Ethernet (PoE) powered, no
external power source is provided. In most

Issue 1, June 2018 Model 374A User Guide
Page 8 Studio Technologies, Inc.
MODEL 374A
INTERCOM BELTPACK
applications an Ethernet switch with the
required PoE capability will be utilized.
Connections
In this section signal interconnections will
be made using the two connectors located
on the bottom of the Model 374A’s enclo-
sure. An Ethernet data connection with
Power-over-Ethernet (PoE) capability will be
made using either a standard RJ45 patch
cable or an etherCON protected RJ45 plug.
A dual-channel or single-channel (dual- or
single-ear) headset will be connected using
a cable-mounted 5-pin male XLR connector.
Ethernet Connection with PoE
A 100BASE-TX Ethernet connection that
supports Power-over-Ethernet (PoE) is
required for Model 374A operation. This
one connection will provide both the Ether-
net data interface and power for the Model
374A’s circuitry. A 10BASE-T connection is
not sufficient and a 1000BASE-T (“GigE”)
connection is not supported unless it can
automatically “fall back” to 100BASE-TX
operation. The Model 374A supports Eth-
ernet switch power management, enumer-
ating itself as a PoE class 1 device. Any
source that is compliant with the IEEE®
802.3af standard will function correctly.
Should the selected Ethernet switch port
support Energy-Efficient Ethernet (EEE) it
must be disabled to help ensure reliable
Dante operation.
The Ethernet connection is made by way of
a Neutrik etherCON protected RJ45 recep-
tacle that is located on the bottom of the
Model 374A’s enclosure. This allows con-
nection by way of a cable-mounted ether-
CON connector or a standard RJ45 plug.
The Model 374A’s Ethernet interface sup-
ports auto MDI/MDI-X so that a cross-over
cable will never be required.
Headset Connection
The Model 374A provides a 5-pin female
XLR connector that interfaces with the
microphone and headphone connections
of an intercom or broadcast-style headset.
Refer to Figure 2 for connection details.
The microphone input connections are
compatible with most unbalanced dynamic
or electret (low-volatge DC-powered)
microphones. A balanced dynamic micro-
phone should, in most cases, also function
correctly if the signal – (low) is connected
to Model 374A’s mic in –/shield connec-
tion. No support is provided for micro-
phones that require P12 or P48 phantom
power.
To allow users of stereo (dual-earpiece or
“double muff”) headsets to hear a monau-
ral version of the two headphone output
channels does not require special wiring of
the 5-pin male XLR mating connector. The
headset’s left headphone channel should
always be wired to pin 4 and the right
headphone channel to pin 5. Configuration
choices, discussed later in this guide, can
then be used to create the desired mon-
aural output. It’s important not to connect
together (short) pins 4 and 5 of the Model
374A’s headset connector as damage to
the Model 374A’s output circuitry could
result.
Figure 2. Headset connection pinout chart

Model 374A User Guide Issue 1, June 2018
Studio Technologies, Inc. Page 9
MODEL 374A
INTERCOM BELTPACK
Monaural (single-earpiece or “single
muff”) headsets should be wired such that
its headphone is wired only to pin 4; pin 5
should be remain unused. Configuration
choices, discussed later in this guide, can
be used to create a monaural output.
It’s possible that some Beyerdynamic
headset interconnecting cable assemblies
terminate the earpiece’s left and right con-
nections opposite from what the Model
374A and other broadcast equipment
require. These cables may terminate the
left earpiece to pin 5 of the XLR connector
and the right earpiece to pin 4. If this con-
dition is present it will require reversing
or “flipping” the two wires in a headset’s
5-pin male XLR connector such that the
left earpiece connects to pin 4 and the
right earpiece to pin 5.
Dante Configuration
For audio to pass to and from the Model
374A requires that several Dante-related
parameters be configured. These configu-
ration settings will be stored in non-volatile
memory within the Model 374A’s circuitry.
Configuration will typically be done with
the Dante Controller software application
which is available for download free of
charge at www.audinate.com. Versions
of Dante Controller are available to sup-
port Windows® and OS X® operating
systems. The Model 374A uses the Ultimo
4-input/4-output integrated circuit to imple-
ment the Dante architecture.
The four Dante transmitter (Tx) channels
associated with the Model 374A’s Dante
interface must be assigned to the desired
receiver (Rx) channels. This achieves
routing the Model 374A’s four talk output
audio channels to the device (or devices)
that will be “listening” to them. Within
Dante Controller a “subscription” is the
term used for routing a transmitter flow
(a group of output channels) to a receiver
flow (a group of input channels). The num-
ber of transmitter flows associated with an
Ultimo integrated circuit is limited to two.
These can either be unicast, multicast, or
a combination of the two. If the Model
374A’s transmitter channels need to be
routed using more than two flows it’s pos-
sible that an intermediary device, such as
the Studio Technologies Model 5422 Dante
Intercom Audio Engine, can be used to
“repeat” the signals.
The four Dante receiver (Rx) channels asso-
ciated with the Model 374A’s audio inputs
also need to be routed to the desired Dante
transmitter (Tx) channels. These four audio
signals can be sent to the Model 374A’s
2-channel headphone output.
The Model 374A supports an audio sample
rate of 48 kHz with no pull-up/pull-down
values available. The Model 374A can serve
as the clock master for a Dante network but
in most cases it will be configured to “sync”
to another device that is serving as the
“grand master.”
The Model 374A has a default Dante
device name of ST-M374A- followed by
a unique suffix. The suffix identifies the
specific Model 374A that is being config-
ured. The suffix’s actual alpha and/or
numeric characters relate to the MAC
address of the unit’s Ultimo integrated
circuit. The four Dante transmitter (Tx)
channels have default names of Ch1, Ch2,
Ch3, and Ch4. The four Dante receiver (Rx)
channels have default names of Ch1, Ch2,
Ch3, and Ch4. Using Dante Controller the
default device name and channel names
can be revised as appropriate for the spe-
cific application.

Issue 1, June 2018 Model 374A User Guide
Page 10 Studio Technologies, Inc.
MODEL 374A
INTERCOM BELTPACK
Model 374A Configuration
Many of the Model 374A’s operating param-
eters can be configured to match the needs
of specific applications. The STcontroller
software application is used to observe a
unit’s current configuration and perform any
changes that are required. No DIP switch
settings or other local actions are used to
configure the unit. This makes it imperative
that STcontroller be available for convenient
use in a personal computer that’s connect-
ed to the related LAN.
STcontroller is available free of charge
on the Studio Technologies website
(www. studio-tech.com/stcontroller) and
is compatible with personal computers
running Windows operating systems that
are version 7 and later. STcontroller versions
1.06.00 and later is required to support the
Model 374A. If necessary, download and
install STcontroller onto a designated per-
sonal computer. This personal computer
must be on the same local area network
(LAN) and subnet as the Model 374A unit
or units that are to be configured.
STcontroller allows observation and selec-
tion of functions that include:
• Microphone input type (dynamic or
electret)
• Microphone preamplifier gain
• Sidetone level
• Mic kill support
• Talk button operation
• Headphone input-to-output channel
routing
Changes made using STcontroller will be
immediately reflected in the unit’s opera-
tion; no Model 374A “reboot” is required.
Each time a change is made the four talk
buttons on the top panel will momentarily
flash orange in a distinctive pattern to indi-
cate that a command from STcontroller has
been received.
Using STcontroller
Immediately after starting STcontroller
the application will locate and display the
devices that it can control. The one or more
Model 374A units that are recognized will
appear in the device list. Use the Identify
command to allow easy recognition of a
specific Model 374A unit. Double clicking
on a device name will cause the associated
configuration menu to appear. Review the
current configuration and make changes
as required.
Microphone Input Type
Choices are Dynamic and Electret.
If the associated headset has a dynamic
(non-powered) microphone select the
Dynamic input type. If the headset has a
microphone that requires low-voltage DC
power for operation select Electret. Note
that the Model 374A cannot supply P12 or
P48 phantom power that may be required
for balanced condenser (capacitor) micro-
phones. This should not pose an issue as
this type of microphone is essentially never
associated with a headset that would be
used for intercom applications.
Microphone Preamplifier Gain
Choices are Low (42 dB) and High (48 dB)
for dynamic input type and Low (22 dB)
and High (30 dB) for electret input type.
A total of four microphone preamplifier
gain settings are provided. Which are
available depends on the configuration
of the microphone input type. Dynamic
microphones have an output level that
is typically lower than that provided by

Model 374A User Guide Issue 1, June 2018
Studio Technologies, Inc. Page 11
MODEL 374A
INTERCOM BELTPACK
electret microphones. As such, the gain
associated with the low and high settings
when the input type is Dynamic are signifi-
cantly greater than the gain choices avail-
able when the input type is Electret.
When the input type is Dynamic the Low
(42 dB) gain setting will be appropriate for
most applications. (Technically this gain is
approximately equal to the gain provided
within an RTS® BP-325 analog party-line
beltpack.) The Low (42 dB) gain setting
could also be valuable should the connect-
ed microphone have a high sensitivity (high
output level for a given acoustical input)
or an enthusiastic user routinely talks loudly
into the microphone. Setting the gain for
High (48 dB) may be helpful in some ap-
plications, such as with headsets that have
a low microphone output level. The higher
gain setting may also be useful when the
Model 374A is going to be deployed at
events where users are not able to speak
at normal levels, e.g., sporting events such
as golf tournaments.
Electret microphones typically have a
higher output level due to their internal
preamplifier. As such less preamplifier gain
is required. Select either the Low (22 dB)
or High (30 dB) setting as appropriate for
the application.
The compressor active LED, visible on
the bottom of the Model 374A’s enclosure
adjacent to the headset connector, can act
as a guide when setting the microphone
preamp gain. During normal talk opera-
tion the compressor active LED should
light intermittently. If, for example, with a
dynamic microphone the LED rarely lights
and the preamp gain is set to Low (42 dB)
it might be a good idea to change it to High
(48 dB). If the LED is lit fully during normal
talking in a situation where the headset has
an electret microphone and the gain is set
for High (30 dB), changing it to Low (22 dB)
might be a good idea.
Sidetone Level
Choices are Off, Low, Medium Low,
Medium, Medium High, and High.
The Model 374A includes a sidetone func-
tion that allows microphone audio coming
from the microphone preamplifier to be
sent to the both channels of the headphone
output. This serves as a user confirmation
that they are actively sending audio to one
or more of the talk output channels. Side-
tone audio will only be routed to the head-
phone output when at least one of the talk
channels is active. The level of the side-
tone audio can be selected from among
five values. The correct value is simply the
one that makes the user most comfortable.
Sidetone audio can also be disabled by
selecting Off. Selecting Off would be useful
only in special applications such as during
troubleshooting or where user talk audio is
being returned as part of their listen audio
signals. The four rotary level controls will
not impact the sidetone level.
Mic Kill Support
Choices are Off, Device ID, Global Kill
Command, and Device ID/Global Kill
Command.
The mic kill function allows an enabled
talk channel to be disabled by remote
control. Specifically, it’s possible to re-
motely change all active (on) talk channels
to their off state. This function is sometimes
referred to as a “talk off” function. There are
two means available to remotely disable all
active talk channels. The Device ID method
uses the identification command generated
by the Dante Controller or STcontroller
applications as a “trigger” to disable

Issue 1, June 2018 Model 374A User Guide
Page 12 Studio Technologies, Inc.
MODEL 374A
INTERCOM BELTPACK
any active talk channels. The Global Kill
Command can be generated by applica-
tions that incorporate the Studio Technolo-
gies’ proprietary method. This method
utilizes sending a data command over the
Ethernet connection. Select the desired
mic kill configuration from the four choic-
es. Off simply means that no remote talk
control is supported.
Talk Button Operation
Choices are Push to Talk, Push to Talk/
Tap to Latch, Talk Disabled, Talk Disabled/
Phones Tap to Latch.
This configuration section allows indepen-
dent selection of how the four talk buttons
will function. When the Push to Talk mode
is selected the operation is self-explanato-
ry. Only when a talk button is pressed and
held will talk audio be sent out its associ-
ated Dante transmitter channel.
When the Push to Talk/Tap to Latch mode
is selected a “hybrid” function of sorts is
enabled. Pressing and holding the talk
button will enable audio to be sent out
its associated Dante transmitter channel.
When the button is released audio will
stop being sent out its associated trans-
mitter channel. Tapping (momentarily
pressing) the button will cause the func-
tion to “latch” into the talk active mode.
Tapping the button again will cause the
function to “unlatch” and talk will no lon-
ger be active.
Many applications are best served when
the buttons are configured in the Push to
Talk mode. This ensures that a channel
can’t accidentally be left in its talk mode.
But there are certainly valid situations
when the Push to Talk/Tap to Latch mode
setting will prove to be very useful.
When the Talk Disabled mode is selected
microphone audio will never be sent out
the associated Dante transmitter channel.
This can be useful when the audio input
associated with this channel is going to be
monitored but talk audio is not allowed to
“join” this specific intercom channel.
When the Talk Disabled/Phones Tap to
Latch mode is selected the associated
button will not impact talk audio but will
instead control the on/off state of the audio
being sent to the headphone output. In
this mode talk audio will never be sent out
the associated Dante transmitter channel.
This is an interesting mode, allowing one
or more Model 374A audio channels to
serve in a “monitor mixer” function. The
button will allow quick on/off control while
the rotary level control can remain in its
desired position.
Headphone Output
Choices are Left, Right, and Left and Right.
Four audio input sources (Dante receiver
channels) can be assigned to the head-
phone output channels using the Dante
Controller application. How these four
audio signals are routed to the Model
374A’s headphone output channels can
be configured using this configuration
choice. The three options provide flexibility
in how the audio sources are presented
to the user. When using a stereo (“double
muff”) headset it’s common for the four
audio input sources to always be routed
to both the left and right channels. But the
Model 374A’s flexibility allows each source
to be independently configured for sending
to the left and right, left only, or right only
headphone channels.
When using a stereo headset sending all
inputs to both channels is often referred to

Model 374A User Guide Issue 1, June 2018
Studio Technologies, Inc. Page 13
MODEL 374A
INTERCOM BELTPACK
as a dual-channel mono output. If a mon-
aural (“single muff”) headset is used the
Left configuration option allows the four
input channels to be combined to monau-
ral so that the listener can simultaneously
hear all the sources.
Operation
At this point everything should be ready
and Model 374A operation can commence.
An Ethernet connection with Power-over-
Ethernet (PoE) capability should have been
made. A headset terminated on a 5-pin
male XLR connector should be plugged
into the headset connector.
Using the Studio Technologies STcontroller
software application the unit’s configura-
tion should have been selected to meet
the needs of the specific application. The
Model 374A’s Dante configuration set-
tings should have been selected using the
Dante Controller software application. In
this way the unit’s four audio output chan-
nels (Dante transmitter channels) and four
audio input channels (Dante receiver chan-
nels) should have been routed, by way of
Dante “subscriptions,” to the receiver and
transmitter channels on associated Dante-
enabled equipment.
Initial Operation
The Model 374A will start to function
as soon as a Power-over-Ethernet (PoE)
power source is connected. However, it
may take 20 to 30 seconds for full opera-
tion to commence. Upon initial power up
the three status LEDs located on the bot-
tom panel below the etherCON RJ45 re-
ceptacle will begin to light as network and
Dante connections are established. The
green and orange LEDs that illuminate the
four pushbutton switches on the top panel
may initially light randomly and then will
light in a test sequence to indicate that the
application firmware (embedded software)
has started. Once the entire sequence has
completed and the Dante connection has
been established full operation will begin.
Ethernet and Dante Status
LEDs
Three status LEDs are located below the
etherCON RJ45 receptacle on the Model
374A’s bottom panel. The LINK ACT LED
will light green whenever an active con-
nection to a 100 Mb/s Ethernet network
has been established. It will flash in re-
sponse to Ethernet data packet activity.
The SYS and SYNC LEDs display the
operating status of the Dante interface and
associated network. The SYS LED will light
red upon Model 374A power up to indi-
cate 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 374A is not
synchronized with a Dante network. It will
light solid green when the Model 374A is
synchronized with a Dante network and an
external clock source (timing reference)
is being received. It will slowly flash green
when this specific Model 374A is serving
as the clock master for the network. It’s
possible that up to 30 seconds may be
required for the SYNC LED to reach its
final state.
Compressor Active LED
A yellow LED indicator is located on the
bottom panel adjacent to the headset
connector. Labeled COMP, the LED dis-
plays the status of the microphone audio
compressor function. It will light whenever
the input level from the microphone, along

Issue 1, June 2018 Model 374A User Guide
Page 14 Studio Technologies, Inc.
MODEL 374A
INTERCOM BELTPACK
with the configured preamplifier gain, is
such that the dynamic range of the talk
signal is being controlled. It’s perfectly
acceptable for this LED to light intermit-
tently whenever a user is talking at a
normal voice level into the associated
microphone. But if the COMP LED lights
solid while a user is talking at a normal
voice level this will typically indicate that
the mic preamp gain setting should be
reduced. Conversely, if the COMP LED
almost never lights when normal talking
is taking place, it’s possible that changing
the mic preamp gain to the higher setting
would be beneficial. Note that due to the
design of the circuitry the compressor
active LED will function whether or not any
of the four talk channels are active.
Headphone Output
Four rotary potentiometers (“pots”), locat-
ed on the Model 374A’s top panel, allow
individual adjustment of the level of the
four audio input signals as they are sent to
the 2-channel headphone output. Depend-
ing on the configuration of the unit, each
audio input can be sent to the left channel,
the right channel, or both the left and right
channels of the headphone output. The
pots are “push in/push out” type which
allow their associated knobs to be in their
“out” position to be adjusted and then
moved to their “in” position when protec-
tion from an unwanted change is desired.
Users should find the headphone output
audio quality to be excellent, with high
maximum output level and low distortion.
Audio signals do not pass directly through
the level pots. The position of the pots is
recognized by the Model 374A’s proces-
sor which then adjusts the signal level
within the digital domain. When a pot is
in its fully counterclockwise position the
associated audio signal is fully muted. In
most cases the on/off status of the four talk
channels does not impact the headphone
output. However, one button configuration
setting (Talk Disabled/Phone Tap to Latch)
assigns the associated button to function
as a channel listen audio on/off selector.
Button Operation
Four pushbutton switches are associated
with the Model 374A’s four talk channels.
How they function will depend on the con-
figuration of the unit. Each button can be
configured independently.
Push to Talk
When a button has been configured for the
Push to Talk mode how it functions is pretty
self-explanatory. Press and hold the button
when headset microphone audio is to be
sent out the associated Dante audio output
(transmitter) channel. The button’s green
LED will light to indicate that the output is
active. The button will not be lit when the
function is not active.
Push to Talk/Tap to Latch
If a button has been configured for the Push
to Talk/Tap to Latch mode operation is a bit
different and certainly more flexible. Press
and hold the button to activate the talk func-
tion. When released the talk function will
turn off. Momentarily pressing (“tapping”)
the button will cause the function to change
states; off-to-on or on-to-off. Whenever the
talk function is active the green LED will
light. The button will not be lit when the
function is not active.
Talk Disabled
A button that is configured to the Talk
Disabled mode will never allow talk audio
to be sent to the associated Dante audio
output channel. But to provide “feedback”

Model 374A User Guide Issue 1, June 2018
Studio Technologies, Inc. Page 15
MODEL 374A
INTERCOM BELTPACK
that the button has been pressed the
button’s green LED will flash rapidly three
times. This says, in effect, “Yes, I recognize
that you pressed the button but I’m not
going to do anything in response!”
Talk Disabled/Phones Tap to Latch
In the Talk Disabled/Phones Tap to Latch
mode the button will never allow talk
audio to be sent to the associated Dante
audio output channel. Instead the button
will operate in a tap to enable/tap to dis-
able (alternate action or “toggle”) manner
and provide an audio channel listen on/off
function. The button’s orange LED will light
whenever audio is being sent to the head-
phone output. The headphone output level
will continue to follow the setting of the
associated rotary level control.
Sidetone Function
The Model 374A includes a sidetone func-
tion that sends microphone audio to both
the left and right headphone output chan-
nels whenever one or more of the talk but-
tons are active. The quality of the sidetone
audio should be excellent and will provide
Model 374A users with a confidence signal
that they are actively talking to other inter-
com users. Sidetone audio will always be
sent to both headphone channels and is
not a configurable choice. This is because
the function is trying to simulate what a
user would hear if they didn’t have a head-
set covering their ears. It is not intended
to indicate to the user which Dante audio
output (transmitter) channel or channels
are actively sending audio.
The exact sidetone level is configured from
among five values within the STcontroller
application. There is also a selection choice
for turning off sidetone. There is no means
of adjusting the sidetone level using any
physical buttons or controls on the Model
374A unit. Also, the four headphone level
controls on the top panel of the unit do not
impact the sidetone level.
In most cases the exact sidetone level set-
ting is not critical and typical users will not
be concerned about revising it to a spe-
cific value. But setting the sidetone level to
something reasonable is important. Setting
the level too low will encourage users to
speak too loudly; setting it too high and us-
ers will be tempted to speak hesitantly. And
while the user isn’t provided with a sidetone
level control or other adjustment means,
should the need arise STcontroller allows
rapid adjustment of the sidetone level. In
most cases the default sidetone level,
Medium, should provide an appropriate
level.
How to Identify a Specific
Model 374A
The Dante Controller software application
offers an Identify command that can be
used to help locate a specific Model 374A.
When Identify is selected it will send a com-
mand to a single Model 374A unit. On that
specific unit the four pushbutton LEDs will
light in a unique pattern. In addition, the
SYS and SYNC status LEDs, located direct-
ly below the etherCON RJ45 receptacle on
the bottom panel, will slowly flash green.
After a few seconds the LED identification
pattern will cease and normal Model 374A
button LED and Dante status LED opera-
tion will resume.
If configured, the Identify command can
also cause the mic kill function to activate.
For details please refer to the next para-
graph of this guide.

Issue 1, June 2018 Model 374A User Guide
Page 16 Studio Technologies, Inc.
MODEL 374A
INTERCOM BELTPACK
Mic Kill Function
The Model 374A includes a mic kill func-
tion, allowing talk buttons that have been
placed in their enabled (on) state to be re-
motely changed to their disabled (off) state.
This allows one or more talk channels on
a specific Model 374A that have been en-
abled to be remotely disabled. The reason
for this function is simple. It’s common in
intercom applications for users to enable
a talk channel and then go “off headset,”
forgetting that they’ve left the talk channel
enabled. While they take a break or go to
lunch, all other users listening to that chan-
nel may hear unwanted audio! Having the
ability to disable this talk channel can be
very useful.
A configurable choice in the STcontroller
software application is used to select which
of the mic kill methods, Device ID or Global
Kill Command, will be active. Either or
both can be enabled as desired. It’s also
possible to disable the mic kill function.
If the Device ID method of activating
mic kill is enabled, whenever the specific
Model 374A is identified using the Iden-
tify command within Dante Controller or
STcontroller all enabled talk channels will
be forced to their disabled state. If the
Global Kill Command method is enabled
the Model 374A will respond to any such
request and force all talk channels to their
disabled state.
Technical Notes
IP Address Assignment
By default the Model 374A’s Ethernet
interface will attempt to automatically
obtain an IP address and associated
settings using the DHCP (Dynamic Host
Configuration Protocol). If a DHCP server
is not detected an IP address will auto-
matically be assigned using the link-local
protocol. This protocol is known in the
Microsoft® world as Automatic Private
IP Addressing (APIPA). It is also some-
times referred to as auto-IP. Link-local
will randomly assign a unique IP ad-
dress in the IPv4 range of 169.254.0.1
to 169.254.255.254. In this way multiple
Dante-enabled devices can be connected
together and automatically function,
whether or not a DHCP server is active on
the LAN. Even two Dante-enabled devices
that are directly interconnected using an
RJ45 patch cable will, in most cases, cor-
rectly acquire IP addresses and be able
to communicate with each other.
An exception does arise when trying to
directly interconnect two Dante-enabled
devices that use Ultimo integrated circuits
to implement Dante. The Model 374A uses
the Ultimo “chip” and, as such, a direct
one-to-one interconnection to another
Model 374A (or other Ultimo-based prod-
uct) is not supported. An Ethernet switch
linking the two units is required to suc-
cessfully interconnect two Ultimo-based
devices. The technical reason that a
switch is required relates to the need for a
slight latency (delay) in the data flow. And
an Ethernet switch will provide this. While
this is certainly an anomaly, since PoE
power is required for Model 374A opera-
tion it’s highly unlikely that an application
would use two Model 374A units without
a PoE-enabled Ethernet switch being
present.
Using the Dante Controller software ap-
plication the Model 374A’s IP address
and related network parameters can be
manually set for a fixed (static) configura-
tion. While this is a more-involved process

Model 374A User Guide Issue 1, June 2018
Studio Technologies, Inc. Page 17
MODEL 374A
INTERCOM BELTPACK
than simply letting DHCP or link-local “do
their thing,” if fixed addressing is necessary
then this capability is available. But in this
case it’s highly recommended that each unit
be physically marked, e.g., directly using a
permanent marker or “console tape,” with
its specific static IP address. If knowledge
of a Model 374A’s IP address has been
misplaced there is no reset button or other
method to easily restore the unit to a default
IP setting.
In the unfortunate event that a device’s IP
address is “lost,” the Address Resolution
Protocol (ARP) networking command can
be used to “probe” devices on a network for
this information. For example, in Windows
OS the arp –a command can be used to
display a list of LAN information that in-
cludes MAC addresses and corresponding
IP addresses. The simplest means of iden-
tifying an unknown IP address is to create
a “mini” LAN with a small PoE-enabled
Ethernet switch connecting a personal
computer to the Model 374A. Then by using
the appropriate ARP command the required
“clues” can be obtained.
Optimizing Network
Performance
For best Dante audio-over-Ethernet perfor-
mance a network that supports VoIP
Quality-of-service (QoS) capability is
recommended. This can be implemented
on virtually all contemporary managed
Ethernet switches. There are even special-
ized switches that are optimized for enter-
tainment-associated applications. Refer to
the Audinate website (www.audinate.com)
for details on optimizing networks for Dante
applications. Also, disable Energy-Efficient
Ethernet (EEE) support on all Ethernet
switch ports that are associated with Dante
devices. Some implementations of EEE
can incorrectly interpret that a connected
device is not present and prevent proper
Dante operation.
Application Firmware Version
Display
There are two ways in which the version
number of the Model 374A’s application
firmware (embedded software) can be
identified. One requires only the Model
374A unit and involves a button-press
sequence performed upon power up.
The other method utilizes the Model 374A
and the STcontroller software application.
Either method may prove to be useful
when working with factory personnel on
application support and troubleshooting.
As part of the Model 374A’s power-up
sequence the unit’s application firmware
(embedded software) version number can
be displayed. This is useful when working
with factory personnel on application sup-
port and troubleshooting. Before connect-
ing the PoE-enabled Ethernet cable, press
and hold the channel 4 talk button. Then
connect the Ethernet cable. Upon applica-
tion of PoE power the Model 374A will go
through its normal power-up sequences
followed by a display of the firmware ver-
sion. The LED associated with the chan-
nel 1 talk button will “flash” to display the
major version number. Then the LED as-
sociated with the channel 2 talk button will
“flash” to display the minor version num-
ber. Once the version number has been
displayed button 4 can be released and
normal operation will begin. As an example
of what would be a typical application firm-
ware display, if the channel 1 talk button
“flashes” once followed by the channel 2
talk button “flashing” two times this would
indicate that application firmware version
1.2 was present in the Model 374A.

Issue 1, June 2018 Model 374A User Guide
Page 18 Studio Technologies, Inc.
MODEL 374A
INTERCOM BELTPACK
A selection in the STcontroller software
application allows the Model 374A’s ap-
plication firmware version to be identi-
fied. Connect the Model 374A unit to the
network and let it connect and start to
function. Then, after starting STcontroller,
review the list of identified devices and
select the specific Model 374A that inter-
ests you. Then select Version under the
Device tab. A page will then display that
will provide lots of useful information. This
includes the application firmware version
and well as details on the firmware present
in the Ultimo integrated circuit.
Application Firmware Update
Procedure
It’s possible that updated versions of the
application firmware (embedded software)
that is utilized by the Model 374A’s pro-
cessor (microcontroller or MCU) integrat-
ed circuit will be released to add features
or to correct issues. Refer to the Studio
Technologies website for the latest appli-
cation firmware file. The unit has the ability
to load a revised file into the MCU’s non-
volatile flash memory by way of a USB
interface. The Model 374A implements a
USB host function that directly supports
connection of a USB flash drive. The
Model 374A’s MCU updates its application
firmware using a file named M374A.bin.
The update process begins by preparing
a USB flash drive. The flash drive doesn’t
have to be empty (blank) but must be in
the personal-computer-standard FAT32
format. Save the new application firmware
file in the root directory with a name of
M374A.bin. Studio Technologies will sup-
ply the application firmware file inside a
.zip archive file. While the application firm-
ware file inside of the zip file will adhere
to the naming convention required by the
Model 374A, the name of the zip file itself
will include the file’s version number. For
example, a file named M374Av1r2MCU.zip
would indicate that version 1.2 of the ap-
plication firmware (M374A.bin) is contained
within this zip file.
Once the USB flash drive is inserted into
the USB interface, located on the main
circuit board under the cover, the unit must
be powered off and again powered on. At
this point the file will automatically load into
the processor’s flash memory. The precise
steps required will be highlighted in the
next paragraphs of this guide.
To install the application firmware file follow
these steps:
1. Disconnect power from the Model 374A.
This will entail removing the Ethernet
connection that is providing PoE power.
2. Remove the cover from the Model 374A.
Begin by removing the four Phillips-
head machine screws (#1 screw driver
tip), two per side. Be certain to save the
screws so that re-assembly will be fast
and painless. Then carefully slide the
cover forward to separate it from the
level controls and buttons and then lift
it off.
3. Locate the USB connector on the main
circuit board. It’s near the channel 1 talk
button. Insert the prepared USB flash
drive into it.
4. Apply power to the Model 374A by
connecting to a Power-over-Ethernet
(PoE) Ethernet source.
5. After a few seconds the Model 374A will
run a “boot loader” program that will
automatically load and save the new
application firmware file (M374A.bin).

Model 374A User Guide Issue 1, June 2018
Studio Technologies, Inc. Page 19
MODEL 374A
INTERCOM BELTPACK
This will take only a few seconds. During
this time period the channel 4 talk button
LED will flash slowly in alternate colors.
Once the entire process is over, taking
approximately 10 seconds, the Model
374A will restart using the newly-saved
application firmware.
6. At this time the Model 374A is operat-
ing under the newly-saved application
firmware and the USB flash drive can
be removed. But to be conservative,
remove PoE power first and then remove
the USB flash drive.
7. Confirm that the desired application
firmware version has been correctly
saved. This can be done by pressing
and holding the channel 4 talk button,
applying PoE power to the Model 374A,
and then “reading” the application firm-
ware version number by first observing
the channel 1 talk button’s LED and then
observing the channel 2 talk button’s
LED. Alternately, the STcontroller soft-
ware application can be used to identify
the application firmware version number.
Whatever method you use, ensure that
the desired version is present.
8. Once the update process has been
completed reverse the steps and reat-
tached the cover using the four machine
screws.
Note that upon power being applied to the
Model 374A if a connected USB flash drive
doesn’t have the correct file (M374A.bin)
in the root folder no harm will occur. If the
correct file is not present upon power up
the channel 4 talk button’s LED will flash on
and off rapidly for a few seconds to indicate
this condition and then normal operation
using the unit’s existing application firm-
ware will begin.
Ultimo Firmware Update
As previously discussed in this guide, the
Model 374A implements Dante connectivity
using the 4-input/4-output Ultimo integrated
circuit from Audinate. The Dante Controller
software application can be used to deter-
mine the version of the firmware (embedded
software) that resides in the Ultimo “chip.”
The STcontroller software application can
also be used to identify the Ultimo’s firm-
ware version. (Use the Version selection
under the Device tab.) The Ultimo firmware
can be updated by way of the Model 374A’s
Ethernet connection. The latest Ultimo firm-
ware file is available on the Studio Technolo-
gies website. The Dante Firmware Update
Manager (FUM) application program is used
to install the Ultimo firmware. This program
is also available for download on the Studio
Technologies website. It’s anticipated that
an updated version of the Dante Controller
software application will include an auto-
mated method of updating Ultimo firmware.
If this comes to fruition then it should offer a
much simpler method of keeping the Ultimo
firmware current.
Model 374A versus Model 374
Some users may be interested in the
differences between the original Model 374
Intercom Beltpack and the newer Model
374A that is described in this guide. A com-
parison chart is available on the Studio Tech-
nologies website. In addition, the following
text provides a summary of the changes:
• All configuration selections for the
Model 374A are performed using the
STcontroller software application. STcon-
troller also allows the version numbers of
the Model 374A’s application and Ultimo
firmware (embedded software) to be
remotely identified.

Issue 1, June 2018 Model 374A User Guide
Page 20 Studio Technologies, Inc.
MODEL 374A
INTERCOM BELTPACK
• Support for electret microphones was
added to the Model 374A. This involved
incorporating a 5 volt DC power source
that is associated with the microphone
input pin. It can be enabled or disabled
as required using STcontroller.
• The configurable microphone input
gain settings were modified to be com-
patible with the increased output level
supplied by electret microphones.
• The DIP switch assembly and the minia-
ture pushbutton switch found on the
Model 374 are not present on the Mod-
el 374A. As such the belt clip no longer
needs to be rotated and its mounting
arrangement has been changed.
• The user-accessible sidetone trim
potentiometer found on the Model 374
is not present on the Model 374A. In
the Model 374A the level of the side-
tone function is configured using
STcontroller.
• The Model 374A offers a second meth-
od of activating the mic kill function.
This allows a data signal, in additional
to the Device ID command, to activate
mic kill.
• The STcontroller software application
now offers the ability to configure the
mic kill function, including allowing it
to be disabled.
Belt Clip
The belt clip is attached to the back of the
Model 374A’s enclosure by way of two
6-32 thread, Philips-head machine screws.
Unlike other the original Model 374 Inter-
com Beltpack units, the belt clip on the
Model 374A will never have to be rotated
as part of the configuration process. (There
are no configuration DIP switches or a
pushbutton switch under the belt clip.) But
if the belt clip does need to be replaced
a #1 Philips-head screw driver would be
the correct tool to remove the machine
screws.
Restoring Factory Defaults
A command in the STcontroller software
application allows the Model 374A’s con-
figuration to be reset to the factory default
values. From STcontroller select the Model
374A for which you want to restore its
defaults. Select the Device tab and then
select the Factory Defaults feature. Then
click on the OK box. The values shown
on the screen should reflect the default
values. They are:
Microphone Input Type: Dynamic
Microphone Preamplifier Gain:
Low (42 dB)
Sidetone Level: Medium
System Mic Kill: Device ID/Global Kill
Command
Button Operation – Channels 1-4:
Push to Talk/Tap to Latch
Headphone Output – Channels 1-4
Input Routes to: Left and Right