User Guide
Issue 1, September 2014
This User Guide is applicable for serial numbers:
M46A-01151 and later
Copyright © 2014 by Studio Technologies, Inc., all rights reserved
www.studio-tech.com
50115-0914, Issue 1
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Table of Contents
Introduction ................................................................... 5
Installation ..................................................................... 10
Configuration ................................................................ 16
Advanced Configuration ............................................... 17
Operation ...................................................................... 20
Advanced Operation ..................................................... 24
Technical Notes ............................................................. 25
Specifications ................................................................ 27
Appendix A—Interfacing with RTS® Matrix
Intercom Systems ......................................................... 28
Appendix B—Interfacing with Riedel® Artist™
Matrix Intercom Systems .............................................. 29
Appendix C—Interfacing with Clear-Com®
Matrix Intercom Systems .............................................. 30
Block Diagram
Model 46A User Guide Issue 1, September 2014
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Issue 1, September 2014 Model 46A User Guide
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Introduction
The Model 46A is designed to interface
2-wire full-duplex party-line (PL) intercom
circuits with 4-wire audio circuits associated with matrix intercom systems. Other
specialized audio system interfacing applications can also be supported. The Model
46A provides two independent full-featured 2-channel interfaces. Each interface
contains two hybrid circuits which include
automatic nulling capability. The analog
circuitry, under software control, provides
excellent audio quality and high return-loss.
The interfaces are compatible with powered
and unpowered 2-wire party-line circuits.
They are capable of supplying DC power,
allowing direct operation of devices such as
user beltpacks. Configuration settings allow the 2-wire and 4-wire interface circuitry
to be compatible with a range of nominal
signal levels. Audio level meters provide
user confirmation of system performance
during setup and operation. Applications for
the Model 46A include television sports and
special event broadcasting, theme park and
theater installations, corporate events, and
industrial testing environments. Standard
audio connectors are used for all input and
output signals. The Model 46A mounts in
one space of a standard 19-inch rack
enclosure and requires 100-240 volts,
50/60 Hz for operation.
2-Wire Interfaces
The Model 46A’s 2-wire interfaces are
optimized for direct connection with
2-channel party-line intercom circuits.
In addition, single-channel party-line
intercom circuits can also be connected.
Many broadcast applications use the
2-channel TW-Series from RTS®, including their popular BP325 beltpack. Other
industry-standard single- and 2-channel
PL intercom systems, including those from
Clear-Com®, are also directly compatible.
To provide optimal signal matching and
interface performance the nominal level of
the Model 46A’s 2-wire interfaces can be
selected. Using DIP switches, accessible
on the front panel, the nominal levels can
be selected to be either –10 or –14 dBu,
settings that should allow compatibility
with virtually all party-line systems. For example, for applications that use equipment
from RTS the –10 dBu setting is appropriate. For other equipment, such as that
from Clear-Com, the –14 setting is correct.
The Model 46A’s 2-wire interfaces can
correctly function with powered (“wet”)
or unpowered (“dry”) intercom circuits.
Model 46A Front Panel
Model 46A Back Panel
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Powered circuits have a DC voltage present, typically provided by power supplies
such as the RTS PS31 or Clear-Com PS-
232. This DC power, normally 30-32 volts,
provides energy for connected devices
such as user stations or beltpacks. In this
type of application the Model 46A is configured to operate in its external 2-wire power
source mode. In this mode the Model
46A’s circuitry maintains the required
high-impedance load and, as in all cases,
draws no power from the party-line circuit.
An auto-terminate function ensures that
should a “wet” circuit not be connected,
the Model 46A’s interface circuitry will
remain stable. This unique feature makes
certain that objectionable audio signals,
including oscillations and “squeals,” will
infrequently be sent to the connected
4-wire device.
A significant capability of the Model 46A’s
2-wire interfaces is their ability to supply
DC power and 200 ohm AC termination
to the connected intercom circuits. Referred to as the Model 46A’s internal 2-wire
power source mode, the 30 volt output can
power devices such as user stations and
beltpacks. In many applications this will
eliminate the need for external intercom
power supplies. Besides reducing total
system cost, this feature can also lower
system weight, reduce required mounting
space, and decrease the mains energy
requirement.
With each 2-wire interface’s ability to supply up to 315 milliamperes (mA) of current,
a typical broadcast application that uses
two sets of three BP325 beltpacks can easily be supported. Each interface’s 30 volt
DC intercom power source ensures that
systems requiring long intercom cable runs
will function correctly. The circuitry’s output
regulation is such that little change in the
output voltage will occur over its entire
rated output current. Also, the unique design of the power supply circuitry virtually
eliminates the noise and “hiss” associated
with typical intercom power supply performance. Under software control the output
of the DC power supplies are monitored
for over-current and short-circuit conditions. This allows protection shut-down
of the output DC, as well as providing an
alert by way of a visual indicator.
Analog Hybrids with Auto
Nulling
A key reason that the Model 46A’s interfaces achieve excellent audio performance
is the design of the 2-wire-to-4-wire hybrid
circuits. They provide low noise and distortion, good frequency response, and
high return-loss (“nulling”), even when
presented with a wide range of 2-wire
conditions. Unlike telephone-line (“POTS”)
oriented DSP-based hybrid circuits, the
Model 46A’s analog circuitry provides extended frequency response. With a pass
band 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,
the 2-wire party-line circuits.
A hybrid’s ability to isolate the transmit
signal from the receive signal in the 2-wireto-4-wire interface is critical. The quality of
this isolation, technically known as returnloss or trans-hybrid loss, is measured in
dB. A high value is important, especially
in applications where multiple 2-wire-to4-wire interfaces are used together. Remote sports broadcast applications are
especially sensitive to this requirement.
The Model 46A’s sophisticated auto nulling function uses analog circuitry under
Issue 1, September 2014 Model 46A User Guide
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microprocessor control to achieve significant trans-hybrid loss. This return-loss
“null” is achieved by making a series of
adjustments to account for the resistive,
inductive, and capacitive conditions that
are present on the connected 2-wire partyline circuit. The party-line’s conditions are
the sum of the impact made by the type
and quantity of cable, the connected userdevices, and the intercom power source.
Whenever a user presses one of the
Model 46A’s auto null buttons digital
circuitry adjusts the analog hybrids to
rapidly achieve their maximum return-loss.
The nulling process takes less than 10
seconds for each channel of an interface.
However, it’s important to note that while
the nulling process is automatic, it only
takes place upon user request. This can
lead to more stable and consistent audio
performance when a hybrid is exposed to
the varying 2-wire conditions often found
in broadcast applications. The parameters obtained during the nulling process
are stored in non-volatile memory; mains
power interruptions won’t require the auto
nulling function to again be performed.
A sine-wave audio tone is generated for
use during the auto nulling process. The
frequency is software-controlled to maximize the ability of the hybrid circuits to
reach a “deep” null. In addition, at the
beginning of each auto null sequence a
short period of 24 kHz tone is sent to the
associated 2-wire party-line interface. This
serves as a microphone disable (“mic kill”)
signal for user devices such as the RTS
BP325. By automatically disabling “open”
microphones the auto nulling process can
achieve better performance.
4-Wire Interfaces
Associated with the 4-wire portion of the
Model 46A’s interfaces are analog line-level
inputs and outputs. These are intended to
interconnect with a variety of 4-wire devices,
including matrix intercom systems, audioover-fiber transmission systems, and other
specialized audio equipment. The input
and output circuitry is transformer-coupled
to minimize the chance of hum, noise, or
ground “loop” issues. A key characteristic
of the Model 46A’s design is the ability to
select the 4-wire input and output nominal
levels. This helps to ensure compatibility
with virtually all audio equipment. Frontpanel-accessible DIP switches allow the
nominal levels to be configured from among
four choices: 0, +4, +6, or +8 dBu. The
0 dBu setting was specifically provided for
compatibility with Clear-Com matrix intercom systems. The +4 dBu setting allows
“standard” audio signals to be directly
connected. Digital matrix intercom systems
from Riedel® can be effectively connected
using the +6 dBu setting. And the +8 dBu
setting allows proper level matching with the
popular ADAM™-Series of matrix intercom
systems from RTS. This setting also applies
to the related RVON-I/O VoIP product.
The Model 46A contains eight 5-segment
LED level meters. Four of the meters are
provided for each interface, with two displaying the level of the signal being received
from the 4-wire source and two displaying
the level being sent to the 4-wire output.
During installation and setup the meters
are invaluable in helping to confirm that the
nominal level DIP switch settings have been
properly made. During normal operation
the meters offer rapid confirmation of audio
signal flow in and out of the unit. Additional
LED status indicators are also provided,
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offering a clear view of the 2-wire DC power
and auto null functions.
Pro Audio Quality
The Model 46A’s audio circuitry was
designed in the spirit of professional
audio equipment, rather than that found
in typical party-line intercom gear. Highperformance components are used
throughout, providing low-distortion, lownoise, and high headroom. Using passive
and active filters, the frequency response
is limited to approximately 100 Hz to 8 kHz.
This range was selected to provide excellent performance for human speech, while
maximizing the ability of the hybrids to
create substantial “nulls.” When the Model
46A’s internal DC power sources are selected to provide 2-wire party-line intercom
power, enhanced audio performance can
also be expected. The quality of the DC
supply circuits is excellent, with very little
noise, hum, or “hiss” being added to the
2-wire connections. In addition, the impedance characteristics of each interface’s DC
powered (“wet”) channels was tailored to
be essentially identical to that of the unpowered (“dry”) channel. This unique situation allows the automatic nulling circuitry
to provide excellent, consistent results
for both the powered and unpowered
channels.
Attention to detail is a hallmark of the
Model 46A’s design. For example, during
the brief auto nulling process an interface
channel’s 4-wire input and output signal is
muted, preventing unwanted audio from
reaching the connected equipment. Associated with the 2-wire interfaces is circuitry
that, under software control, applies 200
ohm terminating impedances to the 2-wire
party-line circuits. This, along with other
circuitry that monitors DC voltages present on the 2-wire circuits, ensures that
audio instability associated with unterminated circuits will rarely occur. As previously mentioned the Model 46A’s 2-wire
DC power sources offer a unique level of
performance. Their ability to deliver power
while maintaining audio quality is simply
unmatched.
Special Applications
While the Model 46A is designed to directly integrate into typical applications,
it’s ready to support the “one-in-a-million”
situations, too. To accomplish this DIP
switches, accessible on the back panel,
allow some of the automatic features to be
disabled. For example, one switch allows
the auto-terminate feature to be disabled.
While this feature can help maintain audio
quality, advanced users might need to disable it. This would allow full control over
the Model 46A’s four hybrid circuits, enabling them to be used completely independently. A second DIP switch changes
the way in which the front-panel auto null
push button switches operate. Normally
pressing one of the buttons begins the
process of auto nulling both channels
associated with an interface. The alternate switch mode allows each auto null
sequence to be activated independently.
One tap (a quick press and release) of the
auto null button will begin the auto null
process for channel 1. Two taps of the
button will begin the auto null process for
channel 2. For installer-selected applications, three opto-coupled inputs allow selected Model 46A features to be remotely
controlled. These features include remote
auto nulling for each interface and remote
“mic kill” activation.
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Simple Installation
The Model 46A uses standard 3-pin XLR
connectors to allow convenient interconnection in most broadcast and general
audio environments. For flexibility, access
to the 2-wire party-line intercom interfaces
can be made using the connectors provided on both the front and back panels.
In permanent installations the back-panel
connectors will typically be utilized. In other
settings, such as field television production, front-panel-access allows intercom
beltpacks to be rapidly connected, without
requiring access to the inside of a rack
enclosure or necessitating the use of a secondary input/output (I/O) panel.
The Model 46A is housed in a rugged aluminum and steel enclosure that is designed
to be “road tough.” It mounts in one space
of a standard 19-inch rack enclosure. The
mains input source can range from 100
to 240 volts, 50/60 Hz allowing direct operation virtually anywhere in the world.
A switch-mode power supply, contained
within the Model 46A’s enclosure, provides
conversion of the mains input power into
the DC voltage required by the intercom
power supply circuits. Also contained
within the unit is a DC-to-DC converter that
creates the voltages required by the analog
and digital circuitry. These efficient power
supplies help to ensure cool, reliable operation in a variety of settings.
it apparent that installing and configuring
existing 2-wire-to-4-wire interface units was
invariably a time-consuming, aggravating
process that required the talent of an expert
to achieve reasonable results. And even
under those constraints the resulting
audio performance was often mediocre.
Any new design had to look at the application in a different way. This led to the
over-riding Model 46A design goal: create
a “new breed of cat,” fundamentally changing how broadcast 2-wire-to-4-wire interface
equipment fit into actual applications.
An important first step was to eliminate the
requirement that a senior technician, along
with a screwdriver, be present during every
installation. (It was universally acknowledged that their time can be better spent
elsewhere!) The need to adjust trim potentiometers, fabricate special cabling and connector straps, use nulling earpieces, etc.,
had to be eliminated. For example, in virtually all instances, input and output levels fall
within just a few dB of their nominal values
and, as such, could be supported with a
limited number of configurable choices.
In addition, it was acknowledged that in
this application analog audio circuitry was
capable of providing excellent audio performance, but that the required manual nulling
process was operationally taxing. By adding digital control to the analog circuitry,
automatic nulling could be performed—the
best of both worlds!
Design Philosophy
While the “bits and pieces” that make up
the Model 46A have been described in
conventional terms, the real strength of the
unit rests in how it integrates and performs
in the “real world.” Before beginning the
Model 46A’s design process, conversations with industry experts quickly made
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Studio Technologies, Inc. Page 9
The next step was to identify resources that
would improve the installation process and
make operation more reliable. This led to
the inclusion of multiple LED level meters,
allowing continuous monitoring of the input
and output signals. It also turned out that
in many applications only a small number
of user devices, such as beltpacks, are
typically connected to 2-wire party-line circuits. By adding DC power sources to the
Model 46A’s 2-wire interfaces, the need
for external intercom power supplies could
often be eliminated.
The final step was to create a physical
package that would provide significant resources in a form that allowed simple and
reliable integration with other equipment.
This was accomplished by including two
2-channel interfaces in a one-rack-space
enclosure. Using standard 3-pin XLR audio connectors would enable rapid installation and troubleshooting. And by making
the Model 46A “universally” powered,
installation in any locale could be directly
supported.
Installation
In this section you will be installing and
interconnecting the Model 46A. The onerack-space unit will be mounted in an
equipment rack. Audio input, audio output, and party-line intercom connections
will be made by way of 3-pin XLR connectors. AC mains power will be connected
by means of a detachable cord set that is
compatible with the Model 46A’s 3-pin IEC
320 C14 inlet connector.
Locating the Model 46A
The Model 46A’s mounting location will
dictate the length of the cable runs needed to link the unit with the connected devices. This is really only a factor in relation
to the 2-wire party-line intercom circuits.
These circuits carry unbalanced audio
which can be susceptible to interference
and crosstalk issues. Intercom circuits
also carry DC power which may make
resistive losses come into the picture. In
general, shorter intercom cable lengths
will assure more reliable and consistent
system performance. Another location
criterion is access to the Model 46A’s front
panel. An optimal location will allow convenient use of the auto null push buttons
and easy observation of the status and
level meter LEDs.
Mounting the Model 46A
Once a mounting location has been selected installation can begin. The Model
46A requires one space (1.75 vertical
inches) in a standard 19-inch (48.3 cm)
equipment rack. Secure the unit into
the equipment rack using two mounting
screws per side.
4-Wire Audio Inputs and
Outputs
System Components
The shipping carton contains the Model
46A Interface and associated user guide.
Units destined for North America and
Japan also include an AC mains cord.
Your dealer or distributor should provide
an AC mains cord for other destinations.
Issue 1, September 2014 Model 46A User Guide
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Two audio line input and two audio line
output signals are associated with the
4-wire section of each of the Model 46A’s
two interface circuits. Connections are
made using standard 3-pin male and
female XLR connectors. Refer to Appendices A, B, and C for details on interconnecting with RTS, Riedel, and Clear-Com
matrix intercom systems.
4-Wire Line Inputs
As previously mentioned, each of the
Model 46A’s two interfaces allows two
analog line-level audio sources to be connected. The source for these signals will
typically be ports on a matrix intercom
system. It’s also possible that the signals
will come from other devices, such as a fiber optic or copper-based audio transmission system. The 4-wire input circuitry is
balanced, capacitor coupled, transformer
isolated, and has an impedance of 13 k
ohms. The line inputs are compatible with
signals that have a nominal level of 0, +4,
+6, or +8 dBu. Configuration switches,
located on the Model 46A’s front panel,
allow the circuitry to be adjusted to match
the connected nominal level. The switches
work in tandem to control both the input
and output nominal levels.
If connecting a source in this manner results
in hum or noise it’s possible that removing
the shield connection from pin 1 can eliminate the issue; “floating” pin 1 will remove
a potential ground current path from the
Model 46A’s earth/chassis ground point
through the shield of a cable. Also, if a hum
or noise issue does arise be certain to confirm that, unless absolutely necessary, the
mating connector’s “shell” isn’t connected
to the cables’ shield or pin 1. Termination of
this “fourth” pin of a 3-pin XLR connector is
often the cause of seemingly inexplicable
noise issues.
With an unbalanced source connect pin 2
to signal high (+ or hot) and both pins 1
and 3 to shield. If connecting an unbalanced
source in this manner results in hum or
noise, connect pin 2 to high (+ or hot) and
pin 3 to shield; leave pin 1 unterminated.
Audio sources are connected to the line
inputs by way of 3-pin female XLR connectors which are located on the unit’s
back panel. Refer to Figure 1 for a detailed
view. Note that pin 1 of these connectors
is internally connected to the Model 46A’s
earth/chassis ground point.
Prepare the mating connectors (males)
so that pin 2 is signal high (+ or hot),
pin 3 is low (– or cold), and pin 1 is shield.
4-Wire Line Outputs
Each of the Model 46A’s two interfaces
provides two analog line-level audio outputs.
These outputs are intended to be connected
to inputs on the devices associated with the
4-wire audio signals. The outputs are capacitor coupled, transformer balanced with
a nominal level of 0, +4, +6, or +8 dBu. As
previously mentioned, the 4-wire nominal
level configuration switches, located on the
Figure 1. Detail of back panel showing line inputs and outputs
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Studio Technologies, Inc. Page 11
Model 46A’s front panel, control the level
of both the line outputs and the line inputs.
The 4-wire line outputs are capable of driving inputs that have impedances as low as
600 ohms, however connecting to loads
of 2 k ohms or greater is preferred. The
line outputs are connected by way of 3-pin
male XLR connectors which are located
on the Model 46A’s back panel. Refer to
Figure 1 for a detailed view.
The mating connectors (females) should
be prepared so that signal high (+ or hot)
is expected on pin 2. Signal low (– or cold)
should be expected on pin 3. The cables’
shields can be connected to pin 1. However, in order to minimize the chance that
ground-interaction problems will arise, pin
1 on each of the line output connectors is
isolated from all Model 46A circuitry and
ground points. “Floating” pin 1 virtually
eliminates the chance that a “ground-loop”
problem will occur.
2-Wire Party-Line Intercom
Connections
The Model 46A’s 2-wire party-line (PL)
intercom interfaces are designed to directly
connect with standard single- and 2-channel party-line intercom devices. Each of the
two 2-channel PL interfaces is compatible
with intercom circuits that have their own
DC power sources. Alternately, the Model
46A can provide the DC power required
by connected intercom user devices. The
internal 30 volt DC intercom power source
is limited to 315 mA of current. This moderate amount of power requires that the type
and number of connected user devices be
selected appropriately.
For convenience, the 2-wire PL intercom
circuits can be connected to the Model 46A
by way of four 3-pin male XLR connectors;
two are located on the back panel and two
on the front. They are organized in groups
of two connectors per interface, one on
the back and one on the front. They are
wired in parallel (“multed”) and provide
access to the identical signals.
2-Channel Intercom Systems
If compatibility with RTS TW systems is
desired the mating connectors (females)
should be wired so that common is on
pin 1, DC with channel 1 audio is on pin
2, and channel 2 audio is on pin 3. This
wiring scheme is correct whether the connected devices are to be powered by an
external source or by means of the Model
46A’s internal power sources.
Single-Channel Intercom Systems
There are two ways of connecting to the
Model 46A’s 2-wire PL intercom connectors when compatibility with Clear-Com
single-channel intercom devices is desired. The most direct method is to prepare the female XLR mating connectors so
that common is on pin 1, power is on pin
2, and audio is on pin 3. With this connection scenario only audio channel 2 (the
channel associated with pin 3 of the Model
46A’s 2-wire PL intercom interface connectors) will be utilized. Pin 2, the Model
46A’s audio channel 1, will only be used
for connecting DC power to the connected
single-channel devices.
In some single-channel PL intercom system applications it may be desirable to
take full advantage of the two channels
associated with each Model 46A interface.
In these applications one might want to
view the Model 46A as providing four 2wire-to-4-wire interface circuits. The Model
46A can certainly be used in this fashion,
but adapter cables will have to
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Page 12 Studio Technologies, Inc.
be prepared. These adapters will “split” the
Model 46A’s 2-wire PL intercom connectors
into two 3-pin male XLR connectors, one
for each audio channel. Pin 1 of the female
3-pin XLR intended to mate with the Model
46A will connect to pin 1 of both 3-pin male
XLR connectors. Pin 2 of the female XLR
will go to pin 3 of the male XLR designated
as channel 1. Pin 3 of the female XLR will
go to pin 3 of the male XLR designated as
channel 2. Refer to Figure 2 for details. Using two adapter cables the Model 46A can
be directly interconnected with four ClearCom intercom circuits. However, power for
the connected devices must be provided
by external power sources. The Model
46A’s ability to supply intercom power will
not be utilized.
Note: It’s critical that the correct configuration settings be made when using the
Model 46A’s interfaces to support four
independent intercom circuits. Specifically,
the 2-wire power source configuration DIP
switches must be set for external. In addition, the auto terminate disable DIP switch
must be placed in its on (up) position.
Refer to the Configuration and Advanced
Configuration sections of this user guide
for details.
Figure 2. Adapter cable wiring diagram
Remote Control Inputs
The Model 46A allows connection of three
externally provided DC signals. These
signals can provide remote control operation of three functions: auto nulling for
interface 1, auto nulling for interface 2, and
a special “mic kill” function. Remote control of the auto nulling functions provides a
resource identical to that of the front-panel
pushbutton switches. The exact manner in
which the buttons and the remote control
inputs operate depends on the setting of
auto null button mode configuration DIP
switch. The “mic kill” function is unique,
only being available using the remote
control input. It causes a 500 millisecond
“burst” of 24 kHz signal to be sent sequentially to both of the 2-wire partly-line
interface channels associated with each
of the Model 46A’s two interfaces. To
clarify, a “mic kill” signal is sent to a total
of four intercom channels whenever the
function is activated. Independent control
of sending “mic kill” signals to interface 1
or interface 2 is not supported. User intercom devices compatible with this 24 kHz
“mic kill” signal include RTS TW-Series
beltpacks such as the BP325.
The opto-coupled remote control inputs
are designed for direct connection with
3.3 and 5 volt DC logic signals. An internal
475 ohm resistor, in series with each optocoupler’s photodiode, acts to limit the
current flow. Signals of up to 32 volts DC
can be safely connected as long as the
current is limited to 20 mA maximum. If
necessary, an external resistor can serve
to limit the current. For example, with a 12
volt DC signal using a 560 ohm, ¼-watt resistor in series with the connection would
be appropriate. With a 24 volt DC control
signal a series resistor of 1.8 k (1800) ohm
Model 46A User Guide Issue 1, September 2014
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is recommended. For correct operation a
minimum current of 2 mA is recommended.
Access to the remote control inputs is provided by means of a 10-pin male “header”
connector which is located on the Model
46A’s circuit board. Refer to Figure 3 for
a view of the connector’s location. The
“keyed” and “shrouded” header follows
a common industry-standard specification: 2 rows of five pins each with 0.1 inch
between rows and pins. The mating connector is intended to be an insulation-displacement (IDC) socket connector such as
the AMP 746290-1. The connector would
be “crimp” terminated onto a piece of
10-conductor flat ribbon cable. This ribbon cable can safely exit the Model 46A
by laying flat between the chassis and the
cover. The ribbon cable can then “fan out”
to loose wires or, better yet, be terminated
onto another connector such as a 9-pin
D-subminiature type.
There are several ways of preparing to
connect to the remote control inputs. The
easiest means is to purchase an interconnecting cable assembly from Studio Technologies, Inc. The cable assembly consists
of a length of ribbon cable with a 10-pin
socket on one end and a 9-pin D-sub female on the other. Contact the factory or
check the website for details. Alternately,
a competent technician can easy fabricate
an appropriate remote control input interconnect wiring assembly. An example of a
partially pre-made assembly is part number
A1AXH-1036G-ND which is available from
Digi-Key (www.digikey.com).
It’s important to ensure that the source
of the remote control signals can meet
the Model 46A’s logic-state and timing
requirements. The Model 46A recognizes
an idle remote control input as one that
has no current flowing through it. An
active remote control input is one that
Figure 3. Location of 10-pin male header connector on the Model 46A printed circuit board
Issue 1, September 2014 Model 46A User Guide
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has current flowing through it for a minimum of 30 milliseconds. A special case
arises when the auto null button operating
mode has been set to independent. This
requires one front-panel button tap to auto
null channel 1 and two button taps to auto
null channel 2. The remote control equivalent for one tap is current flowing for a minimum of 30 milliseconds. The equivalent for
two taps is current that flows for 30 milliseconds, then a minimum no-current period of
30 milliseconds, followed by current flow for
a minimum of 30 milliseconds. The second
period of current flow must come within one
second of the start of the first.
Once the interconnect method and the
source of the control signals have been
selected, refer to Figure 4 for connection
details. Ensure that the connected signals
follow the specified polarity or damage to
the opto-coupled inputs may occur.
It’s important that a competent technician
be available to perform the actual remote
control input connection process. As expected, mating the interconnecting cable
assembly with the Model 46A’s 10-pin
“header” requires removing the unit’s cover.
As such, this must be done only after confirming that all sources of mains power have
been disconnected from the unit.
10-Pin 9-Pin D-Sub
Function Header (P9) Interface Cable
Remote Auto Null Interface 1 + 7 4
Remote Auto Null Interface 1 – 9 5
Remote Auto Null Interface 2 + 2 6
Remote Auto Null Interface 1 – 4 7
Remote “Mic Kill” + 6 8
Remote “Mic Kill” – 8 9
Figure 4. Remote control input pin-out chart
AC Mains Power
The Model 46A operates directly from AC
mains power of 100 to 240 V, 50/60 Hz. As
a “universal mains input” device, there are
no switches to set or jumpers to install. A
3-pin IEC 320 C14 inlet connector on the
Model 46A mates with a detachable mains
cord set. For units shipped to North America and Japan a cord is supplied that has
a North-American (NEMA 15L) standard
plug on one end and an IEC 320 C13 connector on the other. Units bound for other
destinations require that the appropriate
cord set be obtained. The wire colors in
the mains cord should conform to the
internationally recognized color code and
should be terminated according to the following chart:
Connection Wire Color
Neutral (N) Light Blue
Line (L) Brown
Earth/Ground (E) Green/Yellow
Safety Warning: The Model 46A does
not contain an AC mains disconnect
switch. As such, the AC mains cord
plug serves as the disconnection device. Safety considerations require that
the plug and associated inlet be easily
accessible to allow rapid disconnection of AC mains power should it prove
necessary.
As soon as AC mains power is applied
the Model 46A will begin its power-up
sequence. As a “boot up” indication the
power LED and each of the status LEDs
will momentarily light. After the sequence
has completed the power LED will again
light and remain lit. The unit is now fully
functional.
Model 46A User Guide Issue 1, September 2014
Studio Technologies, Inc. Page 15
Configuration
For the Model 46A to support the needs
of specific applications a number of operating parameters must be configured.
These include the 2-wire party-line power
source, the nominal 2-wire level, and the
nominal 4-wire level. Three 4-position DIP
switch assemblies are used to establish
the desired configuration. One DIP switch
assembly is associated with interface 1, a
second is associated with interface 2, and
a third associated with advanced operating features that apply to both interfaces.
Configuration – Interface 1
and 2
The DIP switch assemblies associated
with interface 1 and 2 are accessible on
the Model 46A’s front panel. They provide
identical capability for their respective
interfaces. Refer to Figure 5 for a detailed
view. In this section the four switches associated with interface 1 will be covered in
detail. This information applies to interface
2 as well. The four switches allow selection of the 2-wire party-line power source,
the nominal level for the 2-wire party-line
channels, and the nominal level of the
4-wire inputs and outputs.
2-Wire Party-Line Power Source
DIP switch 1 is used to select whether or
not the Model 46A provides DC power to
pin 2 of connectors associated with the
2-wire party-line intercom channels. Two
3-pin male XLR connectors, one located
on the Model 46A’s front panel and one
on the back panel, are used to interconnect the Model 46A with the intercom user
devices. When switch 1 is in its off (down)
position the Model 46A will not provide DC
power. This switch setting is appropriate
Figure 5. Detail of front panel showing four DIP
switches
when an external intercom power supply
is providing power to the intercom circuit.
In addition to power, it’s expected that the
external power supply will also provide the
required 200 ohm terminating impedance
to both pins 2 and 3.
When switch 1 is in its on (up) position the
Model 46A will provide a 30 volt, 315 mA
maximum source of DC power to pin 2 of
the 2-wire PL intercom connectors. The
Model 46A will also provide 200 ohm terminating impedances for both pin 2 and pin 3
of the party-line connectors. The DC power
and termination capabilities allow direct
powering of 2-channel intercom beltpacks,
such as the RTS BP325. In addition, listenonly beltpacks, such as the Model 34 from
Studio Technologies, Inc. can be directly
connected. There’s also no problem connecting single-channel intercom beltpacks
or user stations.
2-Wire Nominal Audio Level
DIP switch 2 allows adjustment of the nominal audio level for the two 2-wire party-line
channels associated with interface 1. When
the switch is in its off (down) position the
nominal level is –14 dBu. This level is compatible with intercom beltpacks from manufacturers such as Clear-Com. When the
Issue 1, September 2014 Model 46A User Guide
Page 16 Studio Technologies, Inc.
switch is in its on (up) position the nominal
level is –10 dBu. This setting is appropriate when beltpacks from RTS, such as the
BP325, or listen-only talent amplifier units
from Studio Technologies, Inc. are connected. For best Model 46A performance
it’s important that the 2-wire nominal level
selection be made correctly.
on (up) the nominal level is +6 dBu. When
both switches 3 and 4 are in their on (up)
position the nominal level is configured for
+8 dBu.
Advanced
4-Wire Nominal Audio Level
DIP switches 3 and 4 are used to configure
the nominal level of the input and output
circuitry associated with interface 1’s two
4-wire input and output connections. Four
level settings are available: 0, +4, +6, and
+8 dBu. Prior to setting these DIP switches
it’s important to determine the nominal audio level of the equipment connected to the
Model 46A’s 4-wire input and outputs. This
may take a little investigation but is important for obtaining the best possible Model
46A performance.
The 0 dBu setting is provided specifically
for use when a Model 46A is interconnected with a Clear-Com matrix intercom
system. The +4 dBu setting is appropriate
when standard audio lines with “+4” nominal levels are interconnected. The +6 dBu
setting can be appropriate when interconnecting with equipment manufactured in
Europe, such as the digital matrix intercom
systems from Riedel. The +8 dBu setting is
provided specifically when interconnecting
the Model 46A with audio signals associated with an RTS ADAM-Series of matrix
intercom system. This includes the related
RVON-I/O unit.
When DIP switches 3 and 4 are in their off
(down) position the nominal level is set for
0 dBu. When switch 3 is on (up) and switch
4 is off (down) the nominal level is +4 dBu.
When switch 3 is off (down) and switch 4 is
Configuration
Four DIP switches are provided on the
Model 46A’s back panel. They allow the
two interfaces to be configured for several advanced operating modes. Refer to
Figure 6 for a detailed view of these DIP
switches. The available configurations
include auto terminate, auto null button
operation, and factory test.
Figure 6. Detail of back panel showing the
Advanced Mode DIP switches
Auto Terminate
The auto terminate function is designed to
ensure that each 2-wire-to-4-wire interface
circuit remains stable under most operating conditions. Specifically, 200 ohm
impedances are automatically applied to
both pins 2 and 3 of a Model 46A 2-wire
party-line interface when that interface is
configured for external power and no external source of intercom power is detected on pins 2 or 3. This function is directly
compatible with RTS TW-Series intercom
Model 46A User Guide Issue 1, September 2014
Studio Technologies, Inc. Page 17
applications in which the three conductors
of a cable support both DC power and two
channels of audio. It’s also compatible in
situations where all three conductors of a
Clear-Com single-channel intercom circuit
are connected to the Model 46A. In this latter case only one of the Model 46A’s audio
channels will be used.
There may be situations where it’s necessary for the two channels associated with
each Model 46A interface be used with
separate 2-wire party-line circuits. An example of this might be where two “loops”
of single-channel beltpacks, such as units
from Clear-Com, need to be connected.
Adapter cables as shown in Figure 2 would
be used. In this case the intercom circuit’s
DC power will not be connected to the
Model 46A, but only to the user devices. In
this scenario, a DC voltage won’t be present on pin 2 or pin 3. Another example of
this might be where adapter boxes with DC
blocking are used to interconnect intercom
circuits with the Model 46A. In both these
cases a DC voltage won’t be present on
either pin 2 or 3 and the Model 46A will automatically apply 200 ohm terminations. In
both these cases the termination will be in
error and will result in incorrect audio levels
due a “double-termination” condition.
To prevent this problem the auto terminate
function can be disabled. Referring to Figure 7, when DIP switch 1 is in its off (down)
position the auto terminate function is active. When switch 1 is in its on (up) position the auto terminate function associated
with each interface is disabled. Repeating
for clarity, the auto terminate function applies to both interfaces 1 and 2. With the
auto terminate function disabled the two
interfaces, when set for external power, will
operate normally with the exception that
Figure 7. DIP Switch 1—Auto Terminate
pins 2 and 3 will never be terminated by
the Model 46A’s circuitry.
The auto terminate function should be
disabled only when absolutely necessary;
it’s possible that a significant downside
could be experienced. With auto terminate
disabled it’s important that properly terminated 2-wire party line-intercom circuits
be connected to pins 2 or 3 on the Model
46A’s 2-wire PL connectors. If they are not
connected, it’s likely that audio oscillations, noise, and distortion will be generated in the Model 46A’s 2-wire-to-4-wire
converter circuitry. These audio artifacts
will not cause any damage, but will be
sent out the 4-wire line output connectors.
Users of the 4-wire equipment may be less
than pleased with what they hear!
Auto Null Button
One pushbutton switch is associated with
each of the Model 46A’s two interface
circuits. An advanced configuration parameter allows selection of the button’s
operation. The choices are dual auto null
mode and independent auto null mode.
When dual auto null mode is selected a
single tap of one of the two front-panel
pushbutton switches initiates a routine
that begins with channel 1’s auto null sequence taking place followed immediately
by channel 2’s auto null sequence being
performed. Note that the mode selected
Issue 1, September 2014 Model 46A User Guide
Page 18 Studio Technologies, Inc.
for auto null button operation will also
apply to the remote auto null inputs.
The independent auto null mode allows
the auto null function to be initiated for
each channel as desired. A single tap will
start the auto null routine for channel 1.
Two taps will start the routine for channel 2.
When DIP switch 2 is in its off (down) position the dual auto null mode is selected.
This is provided specifically for cases where
the Model 46A’s 2-wire party line interfaces
will be used with dual channel intercom
user devices. As an example: the RTS TWSeries provides two independent audio
channels, as well as power, over a single
3-conductor cable. In a case such as this
it’s useful for both of the hybrid circuits
associated with an interface to be auto
nulled at approximately the same time.
The dual auto null mode allows a single
tap of the button to initiate nulling of both
hybrid circuits.
Referring to Figure 8, when DIP switch 2
is in its on (up) position the independent
auto null mode is selected. This would
be appropriate for applications in which
the two audio paths associated with each
interface are used with independent partyline intercom circuits. This situation might
arise when two Clear-Com single-channel
intercom circuits are connected to one of
the Model 46A’s 2-channel interfaces. The
hybrid circuit associated with each channel can be auto nulled as desired. Another
example would be in an RTS TW-Series
application that uses source assignment
panels. The “SAP” panels would be used
to route multiple intercom channels to various sets of user devices as desired. In this
case, the two channels associated with
each Model 46A interface will often end up
not routed to the same user device; independent auto nulling is certainly desired.
Factory Test
Back-panel DIP switch 4 is used to select
between normal mode and factory test
mode. Referring to Figure 9, when DIP
switch 4 is in its off (down) position the
Model 46A operates in its standard fashion. When DIP switch 4 is in its on (up)
position the factory test mode is selected.
As expected, when the Model 46A is
deployed in the field DIP switch 4 should
remain in its off (down) position. No damage to the Model 46A or connected equipment will occur when factory test mode is
active.
Figure 9. DIP Switch 4—Factory Test
Figure 8. DIP Switch 2—Auto Null Button
Model 46A User Guide Issue 1, September 2014
Studio Technologies, Inc. Page 19
Operation
Technician intervention is typically not
required during normal Model 46A operation. The unit is designed for continuous
operation with no routine maintenance
necessary. Activating the auto null functions may be warranted should connected
user devices or wiring associated with the
2-wire party-line intercom be changed.
Upon power-up the Model 46A will go
through a short initialization sequence
before normal operation will begin. The
power and status LEDs will each light
sequentially and, upon completion, the
power LED will light steadily. The settings
for the four hybrid circuits are stored in
non-volatile memory and will be recalled
during the power-up process.
Level Meters
The Model 46A contains eight 5-segment LED level meters. These meters
are provided as a support aid during
installation, configuration, operation, and
troubleshooting. The meters represent the
signals coming in from, and going out to,
the 4-wire connections. The meters are
organized in four groups each representing one input and one output. They are
calibrated to reflect the level in dB relative
to the configured nominal operating level.
This is similar to the way in which now-legacy VU meters functioned. As an example
let’s take the situation where the nominal
operating level of interface 1 is configured
for +4 dBu. The LEDs labeled –18, –12,
–6, and 0 of the TO 4-wire ch 1 meters are
lit. (For this example, the level on pin 2 of
interface 1’s 2-wire PL circuit is just large
enough to light the 0 LED.) This indicates
that a signal with the approximate level
of +4 dBu is present on the associated
4-wire output connector. Another example
would be a Model 46A interface configured
for +8 dBu operation and –18 and –12 dB
LEDs are lit. This would indicate that a signal with an audio level of approximately
–4 dBu is present on its associated output.
Each level meter contains four green LEDs
and one yellow LED. The four green LEDs
indicate signal levels at or below the configured nominal level. The top LED is yellow in color and indicates a signal that is
6 dB or greater than the 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
warning that at some stage reducing the
signal level may be prudent. Operation with
normal signal levels should find the meters
lighting near their 0 dB point. Signal peaks
may cause the yellow LEDs to flash. But a
yellow LED that lights fully during normal
operation will typically indicate a signal
level or configuration problem.
If the FROM 4-wire meters display consistency lower or higher levels than their 0 dB
points it’s possible that a configuration issue exists. One potential problem is incorrectly set 4-wire nominal audio level DIP
switches for one or both of the Model 46A’s
interfaces. If the nominal level is set too
low then sufficient audio headroom might
not be available. It can also result in excessively-high audio signals being sent to
2-wire party-line circuits. Setting the nominal level for too high a value will reduce the
signal-to-noise performance. And, as expected, it may also result in audio signals
being sent to the 2-wire circuits at too low
a level. Begin a review by confirming that
the two 4-wire level DIP switches associated with each interface are set as required.
Issue 1, September 2014 Model 46A User Guide
Page 20 Studio Technologies, Inc.
If the Model 46A’s 4-wire nominal levels are
set correctly but the meters still reflect suboptimal levels, the issue may be related to
incorrect settings on the equipment connected to the 4-wire inputs and outputs. It’s
possible that although a connected 4-wire
device’s nominal level matches the Model
46A’s level setting, its actual nominal level
may be significantly different. With a digital
matrix intercom system this problem could
be due to an incorrect configuration having
been made to a specific channel or port.
For example, the RTS ADAM system has
a published nominal level of +8 dBu, but
using its configuration software it’s possible
to set panels or ports to a level different
than nominal. The best solution in this case
is to adjust the intercom system so that its
levels comply with its own published nominal. This should, at least in theory, lead to
the best system performance, including
correct interfacing with the Model 46A. But
often it’s impossible to “clean up” the levels
of a existing system. In this case it may be
necessary to revise the Model 46A’s 4-wire
nominal level settings to match the reality
of the connected signals.
It’s also possible that an error is present on
the 2-wire party-line circuit. Signal levels
associated with 2-wire party-line circuits
depend on a single termination being present. This termination, typically 200 ohms,
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 circuit, will cause a
“double-termination” condition. This leads
to a nominal 100 ohm line impedance
which will result in a level drop of at least
6 dB. Removing the unwanted termination
is really the only valid means of correcting
the problem.
Connecting Party-Line Devices
The Model 46A’s two 2-channel interface
circuits allow two sets of user devices to
be connected. Depending on the setting
of the configuration DIP switches, either
an external intercom power source or the
Model 46A’s internal 2-wire power source
has been designated for supporting the
connected user devices.
External Power Source
The TO 4-wire meters display the level of
signals that come from the 2-wire party-line
circuits and go out the 4-wire interfaces. An
issue may arise if the signals coming from
the connected party-line user devices aren’t
at a sufficient level so that a normal meter
display can be reached. This could be the
result of an incorrectly configured 2-wire
nominal audio level. Confirm that the DIP
switch, associated with each interface, is
set to match the nominal level of the connected devices. RTS user devices have a
nominal level of –10 dBu; Clear-Com devices typically have a –14 dBu nominal level.
When set for an external 2-wire power
source, the Model 46A will not provide
power on pin 2 of the 2-wire connectors,
nor will the Model 46A use any power from
a connected intercom circuit. As expected,
audio signals will be sent from, and received by, each interface’s two audio circuits. In this mode of operation the Model
46A acts as a typical user station on the
connected intercom circuit.
As a connection confirmation, hardware
and software in the Model 46A monitors
pins 2 and 3 of the 2-wire PL intercom
connectors for the presence of DC voltage.
A level greater than approximately 18 volts
Model 46A User Guide Issue 1, September 2014
Studio Technologies, Inc. Page 21
DC on pin 2 will cause the status LED labeled pin 2 to light. A level greater than 18
volts DC on pin 3 will cause the pin 3 status
LED to light.
The author is aware that user intercom devices almost always draw power from pin 2
rather than pin 3. However, in many broadcast applications, power is provided on
all intercom paths so that flexible channel
assignments can be made. In the external
2-wire power mode the Model 46A is simply an observer; whether intercom power is
present on pin 2, pin 3, or both pins 2 and
3 is not significant.
So that the Model 46A’s 2-wire-to-4-wire
interface circuits remain stable and don’t
generate audio artifacts, an auto terminate
feature is implemented. This maintains a
200 ohm termination on both pins 2 and 3
so long as neither of the 2-wire power status LEDs is lit. To clarify, if either, or both,
the LEDs are lit then both terminations are
removed. It was felt that this method would
provide a fairly accurate indication that an
active intercom circuit is connected. In this
case the 200 ohm termination is expected
to be provided elsewhere, typically as
part of the external power supply, and the
Model 46A’s termination is “lifted.”
Internal Power Source
When an interface’s front-panel DIP switch
is set for internal 2-wire power the Model
46A’s 2-wire party-line interface supplies 30
volt DC on pin 2 of the output connector. A
maximum current draw of 315 mA is available. This current is sufficient to power various intercom user devices such as small
user stations and beltpacks. A common
broadcast application would be to use RTS
BP325 beltpacks. Select the connected
devices so that their total current doesn’t
exceed 315 mA. That’s not always the easi
est figure to calculate but a web search will
generally find specifications for all commonly used devices. For example, a search
finds that the original version of the BP325
consumes a maximum of 85 mA of current.
According to this figure up to three of these
units can be connected to each Model 46A
interface. Newer versions of the BP325 use
surface mount component technology and
have a lower maximum current draw of
65 mA. Four of these “modern” BP325
units can easily be supported.
The Model 46A’s intercom power supply
circuits operate under software control.
This allows detection of fault conditions
and protection of both the Model 46A’s
circuitry and connected intercom user devices. Upon initial Model 46A power up no
monitoring of the intercom power output
takes place for a period of three seconds.
This allows the Model 46A’s circuitry and
the connected intercom user devices to
stabilize. The LED associated with pin 2 will
light to indicate that the output is active.
After this initial 3-second period monitoring
becomes active. A fault condition is detected if the power on pin 2 falls below 24
volts for a continuous one second interval. The hardware and software responds
to this condition by turning off the power
source to pin 2 and flashing the pin 2 LED
as a warning. After a 6-second “cool-down”
interval the output returns to the same condition as upon initial power up: power is
again applied to pin 2, the pin 2 status LED
will light, and monitoring won’t begin for
another three seconds. A full short-circuit
condition applied to the Model 46A’s 2-wire
connectors will result in a continuous cycle
of 4-seconds on (three seconds for start
up and one second for detection) and
6-seconds off.
Issue 1, September 2014 Model 46A User Guide
Page 22 Studio Technologies, Inc.
As a diagnostic aid the 2-wire power status
LED associated with pin 3 remains active in
the internal power mode. Whenever DC in
excess of approximately 18 volts is present
on pin 3 the LED will light. This condition
will normally never exist but could prove
useful in special circumstances.
Auto Null
Each of the Model 46A’s 2-channel interfaces has circuitry to automatically null the
two 2-wire-to-4-wire interfaces. Normally
this process is performed at the time of initial Model 46A configuration but there’s no
reason why “auto nulling” can’t be initiated
anytime one desires. The only time that
auto null must be performed is if conditions
have changed vis-à-vis the intercom user
devices and wiring connected to a Model
46A 2-wire PL interface connector. Even a
slight change to an intercom circuit, such
as adding or removing a section of cable,
is sufficient to require that the auto null
process be performed.
Two buttons, one associated with each
interface, are provided to activate the
auto null process. Refer to Figure 10 for a
detailed view. To initiate auto null simply
requires tapping a button. The process
begins by nulling channel 1 of an interface
and, when completed, moves on to channel 2. Two LEDs provide a visual indication
of the auto null process, flashing when the
auto null process for its respective channel
is active.
Figure 10. Detail of front panel showing auto
null section
that are compatible with the RTS TW-Series
“mic kill” protocol. The actual auto nulling
process will next be performed. A series of
tones will be sent out the 2-wire interface.
Other Model 46A circuitry, under software
control, will rapidly perform adjustments to
achieve the best null possible. After the adjustments are made the results are stored
in non-volatile memory. Once the process
has completed the 4-wire input and output
paths are again activated.
Advanced configuration DIP switch 2, located on the back panel, allows an independent auto null button mode to be selected.
If DIP switch 2 is in its on (up) position, the
front-panel pushbuttons will function in
quite a different manner. In the independent
mode, a single tap of a button will cause
channel 1 to auto null. Two taps will cause
channel 2 to auto null. By observing the
operation of the two auto null status LEDs
it will become readily apparent which of the
button modes has been selected.
An actual auto null sequence starts by
muting the 4-wire input and output signal
paths associated with the specific channel
to be nulled. Then a short period of 24 kHz
signal is sent out the 2-wire PL intercom
interface channel. This will turn off microphones on those connected user devices
Model 46A User Guide Issue 1, September 2014
Studio Technologies, Inc. Page 23
If possible, prior to performing an auto null
it’s polite to warn all personnel who are
actively using the connected intercom devices. The tones sent to the 2-wire intercom
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 might be a good time to ask them
to mute any active microphones. While
the automatic “mic kill” signal will apply
to many user devices it may not apply to
all. Muting microphones is significant as
obtaining a “deep” null requires that no
extraneous signals be present on the intercom circuit.
Advanced Operation
The Model 46A allows several of the operating parameters to be configured to meet
the needs of specific applications. The
following paragraphs provide details about
the auto terminate disable and factory test
modes.
Auto Terminate
As previously discussed in this user guide,
the auto terminate function can come into
play when a 2-wire interface is configured
for external power. Using a combination
of hardware and software, pins 2 and 3
of each 2-wire PL intercom connector are
monitored for the presence of DC voltage.
If a level of greater than approximately
18 volts DC is not detected on either pin,
200 ohm terminating networks are applied to those same pins. This ensures
that the Model 46A’s hybrid circuitry remains stable, preventing objectionable
audio signals from being sent to the 4-wire
output connectors. One caveat does apply; there may be a few seconds of severe
noise whenever an interface moves from a
DC present condition to a DC not present
condition. But other than that period, the
audio paths will remain “clean.”
As a visual aid, LEDs on the front panel
will display the DC power status of pins
2 and 3. But when auto terminate is not
active the LEDs will no longer indicate the
intercom circuit’s termination status.
For special externally powered 2-wire applications the auto terminate function can
be disabled. This primarily will come into
play when “splitting” the Model 46A’s resources into four separate single-channel
interfaces. Moving advanced configuration
DIP switch 1, located on the Model 46A’s
back panel, to its on (up) position disables
the auto terminate function. To someone
observing only the Model 46A’s front panel this change would not be readily apparent. The front-panel LEDs will continue to
display the DC power status of pins 2 and
3. But whether or not either or both LEDs
are lit, the Model 46A will never apply 200
ohm terminations to pins 2 or 3. For the
hybrid circuits to remain stable termination impedances must be provided by the
connected circuits. If these are not present one should expect the hybrid circuits
to generate a very impolite noise. This
condition, caused by the 2-wire output
circuitry being in an “unloaded” state, will
not damage the Model 46A’s circuitry. But
errors in cable “patching,” a disconnected
cable, or other real-world issues, can lead
users listening to signals that originate in
the Model 46A’s 4-wire outputs from being
presented with a rude surprise!
In conclusion, it’s important that technical
personnel working with the Model 46A be
informed when the auto termination function has been disabled. They will then be
aware of the potential noise issues and be
ready to make corrections should a problem arise.
Issue 1, September 2014 Model 46A User Guide
Page 24 Studio Technologies, Inc.
Factory Test
Back-panel DIP switch 4 allows a factory
test mode to be enabled. During normal
operation DIP switch 4 should remain in
its off (down) position. When DIP switch
4 is in its on (up) position factory mode is
active. Enabling this mode will result in the
following operating condition: during an
auto null sequence the associated 4-wire
output channel will remain active. This will
allow the tones associated with the nulling
process to be present on the 4-wire output. While not appropriate during actual
Model 46A use, it is interesting to “hear”
the nulling process take place. But unless
directed by factory personnel DIP switch 4
should remain in its off (down) position.
Technical Notes
Software Version Display
A special Model 46A power-up sequence
allows the unit’s software version number
to be displayed. This is useful when working with factory personnel on application
support and troubleshooting situations.
The five meter LEDs associated with
FROM 4-wire channel 1 of interface 1 are
used to display the major release number
with a range of 1 through 5. The five meter
LEDs associated with TO 4-wire channel
1 of interface 1 are used to display the
release sub-number which again ranges
from 1 through 5. Refer to Figure 11 for
a detailed view of the meter LEDs and
the corresponding software version numbering scheme. The Model 46A’s initial
software release is version 1.1 which is
represented by the –18 LEDs of each
meter column being lit.
Major Release Number Release Sub-Number
O 4 .4 O
O 3 .3 O
O 2 .2 O
1 .1
Figure 11. Detail of front panel showing the status LEDs that display the software version. In this
example, the software version is 1.1.
Model 46A User Guide Issue 1, September 2014
Studio Technologies, Inc. Page 25
To display the Model 46A’s software version is very simple. From the powereddown state, press and hold the auto null
button associated with interface 1. Apply
mains power while continuing to press the
button. The normal power-up sequence
will occur and then one LED will be lit in
the column associated with FROM 4-wire
channel 1 of interface 1 and one LED will
be lit in the column associated with TO
4-wire channel 1 of interface 1. As previously described, these two LEDs represent the unit’s current software version.
After the software version number has
been “read” the auto null button can be
released. At this time the unit will begin
normal operation.
Note that while it’s easy to determine
which software version is loaded into the
Model 46A a trip back to the factory is
required to update it. The 8-bit microcontroller that provides the unit’s logic “horsepower” also includes internal FLASH
memory. This non-volatile memory is used
to store the operating software (“firmware”). Re-programming this memory
requires using a specialized programming
unit. While not outrageous in price, it still
costs in the range of US$500. The “programmer” uses a ribbon cable and socket
to interface with a 6-pin “header” on the
Model 46A’s printed circuit board. And, as
you would guess, once connected reprogramming takes only a matter of seconds.
But unfortunately the programmer is not
something that would be found in a typical
“field shop” or repair facility.
Not a TW-12B Replacement!
The Model 46A will provide a high level
of performance over its range of intended
tasks. But it’s not intended to act as a
“universal” 2-wire-to-2-wire interface such
as is provided by the venerable Clear-Com
TW-12B. The Model 46A’s 2-wire interfaces are not isolated from each other;
they share the Model 46A’s internal power
supply’s common connection. (The power
supply common point is DC isolated from
chassis and earth ground.) Specifically,
pin 1 on the XLR connector associated
with interface 1’s 2-wire party-line interface is electrically connected to the pin 1
connection on interface 2. This is due to
the fact that both 2-wire party line interfaces are capable of supplying DC power
to connected devices. They also use the
resources of a single set of logic circuitry.
And as such they each require access to
the Model 46A’s common power supply
circuitry. There’s no doubt that a Model
46A could be used to create a 2-wire-to2-wire party line “bridge” by cross-linking the 4-wire inputs and outputs using
standard XLR audio cables. But it’s likely
that a significant “ground loop” would be
created through pin 1 of each of the Model
46A’s 2-wire interfaces. While it’s possible
to use a set of special isolation transformers to eliminate the ground loop, that’s
best left to the brave of heart!
Model 72 Interface
And now for a shameless “product plug.”
Studio Technologies, Inc. manufactures
a nifty product called the Model 72 Level
Meter/Interface. A compact, standalone
unit, it can prove very useful when setting
up, maintaining, and troubleshooting intercom circuits. It will give a direct indication
of signal levels at any point in a single- or
2-channel intercom circuit. Check it out!
Issue 1, September 2014 Model 46A User Guide
Page 26 Studio Technologies, Inc.
Specifications
General Audio:
Frequency Response:
Distortion (THD+N): <0.5%, measured at 1 kHz,
4-wire input to 2-wire interface pin 2
Signal-to-Noise Ratio: >55 dB, measured at
1 kHz, 4-wire input to 2-wire interface pin 2
Connectors:
Inputs from 4-Wire:
Outputs to 4-Wire:
2-Wire Party-Line Intercom:
Remote Control: 10-pin header, requires optional
10-pin ribbon connector assembly
AC Mains: 3-blade, IEC 320 C14 (mates with
IEC 320 C13)
2-Wire Party-Line Intercom Interfaces: 2
Type: 2-channel party-line (PL), unbalanced
(pin 1 common; pin 2 channel 1 audio or DC with
channel 1 audio; pin 3 channel 2 audio)
Compatibility: single- and 2-channel intercom
systems such as from RTS® and Clear-Com®
Impedance, External Power Mode:
Impedance, Internal Power Mode:
Nominal Level: –10 or –14 dBu, selectable
“Mic Kill” Signal: square wave, 24 kHz, ±1%
Internal Power Source:
315 mA maximum
Hybrids: 4, 2 per interface
Topology:
for resistive, inductive, and capacitive 2-wire partyline loads
Nulling Method: automatic upon user initiation,
processor implements digital control of analog circuitry; null settings stored in non-volatile memory
Nulling Line Impedance Range: 120-350 ohms
Nulling Cable Length Range: 0-3500 feet, typical
Trans-Hybrid Loss:
3-section analog circuitry compensates
±2 dB 100 Hz to 8 kHz
3-pin female XLR
3-pin male XLR
3-pin male XLR
>10 k ohms
200 ohms
30 volts DC nominal,
>40 dB, typical at 800 Hz
4-Wire Outputs: 4, 2 per interface
Type: transformer-coupled, capacitor isolated
Impedance: 50 ohms nominal
Nominal Level: 0, +4, +6, or +8 dBu, selectable
in tandem with nominal input level
Maximum Level: +20 dBu into 2 k ohms
Meters: 8
Function:
outputs
Type: 5-segment LED, modified VU ballistics
Remote Control Inputs: 3
Type:
Input: 3-32 volts DC; 2 mA minimum for operation,
20 mA maximum
Functions:
and “mic kill”
AC Mains Requirement: 100-240 volts (–15/+10%),
50/60 Hz, 34 watts maximum
Dimensions (Overall):
19.0 inches wide (48.3 cm)
1.72 inches high (4.4 cm)
8.4 inches deep (21.3 cm)
Mounting: one space (1U) in a standard 19-inch
rack
Weight: 4.6 pounds (2.1 kg)
Specifications and information contained in this
User Guide subject to change without notice.
displays level of 4-wire inputs and
optically coupled
auto null interface 1, auto null interface 2,
4-Wire Inputs: 4, 2 per interface
Type: transformer-coupled, capacitor isolated
Impedance: 13 k ohms
Nominal Level: 0, +4, +6, or +8 dBu, selectable
in tandem with nominal output level
Maximum Level: +22 dBu
Model 46A User Guide Issue 1, September 2014
Studio Technologies, Inc. Page 27
Appendix A
Interfacing RTS® Matrix Intercom Systems with the Model 46A Interface
ADAM™ Matrix Intercom System Analog Ports to
Model 46A Interface
RVON-I/O I/O Connections to Model 46A Interface
Issue 1, September 2014 Model 46A User Guide
Page 28 Studio Technologies, Inc.
Appendix B
Interfacing Riedel® Artist™ Matrix Intercom System Analog Ports with the
Model 46A Interface
Model 46A User Guide Issue 1, September 2014
Studio Technologies, Inc. Page 29
Appendix C
Interfacing Clear-Com® Matrix Intercom System Analog Ports with the
Model 46A Interface
Issue 1, September 2014 Model 46A User Guide
Page 30 Studio Technologies, Inc.
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