Data Sheet

output. During installation and setup the meters are invalu-
able 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, offering a clear view of the 2-wire DC power and
auto null functions.
Pro Audio Quality
The Model 47’s audio circuitry was designed in the spirit
of professional audio equipment, rather than that found in
typical party-line intercom gear. High-performance components
are used throughout, providing low-distortion, low-noise, and
high headroom. Using passive and active 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 47’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 power sources is excellent, with very little
noise, hum, or “hiss” being added to the 2-wire connections.
Attention to detail is a hallmark of the Model 47’s design. For
example, during the brief auto nulling process an interface
channel’s 4-wire input and output signal is muted, prevent
-
ing 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
47’s 2-wire DC power sources offer a unique level of perfor
-
mance. Their ability to deliver power while maintaining audio
quality is simply unmatched.
Special Applications
While the Model 47 is designed to directly integrate into typi-
cal 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 DIP 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 47’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 pushbutton 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 of the auto null button will begin the auto null process for
interface one. Two taps of the button will begin the auto null
process for channel two. For installer-selected applications,
three opto-coupled inputs allow selected Model 47 features
to be remotely controlled. These features include remote auto
nulling for each interface and remote “mic kill” activation.
Simple Installation
The Model 47 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 belt packs 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 47 is housed in a rugged steel enclosure that is
designed to be “road tough.” It mounts in one space (1U) 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 47’s enclosure, provides conver
-
sion of the mains input power into the DC voltage required
by the party-line 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.
Design Philosophy
While the “bits and pieces” that make up the Model 47 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 47’s design process, conversations
with industry experts quickly made 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 47 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
Studio Technologies, Inc. Model 47 Interface, Issue 2, Page 3