Datasheet

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 47A’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 re
-
sponse 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 47A’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 47A’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 47A’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 47A is designed to directly integrate into typical
applications, it’s ready to support the “one-in-a-million” situa
-
tions, 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 qual
-
ity, advanced users might need to disable it. This would allow
full control over the Model 47A’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 pushbut
-
ton 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 47A features
to be remotely controlled. These features include remote auto
nulling for each interface and remote “mic kill” activation.
Simple Installation
The Model 47A 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 47A is housed in a rugged aluminum and 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 47A’s enclosure,
provides conversion 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 47A 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 47A’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 47A 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
Studio Technologies, Inc. Model 47A Interface, Issue 1, Page 3