Datasheet

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. 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 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, prevent
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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 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” situa
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tions, 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 qual
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ity, 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.
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 enclo
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sure 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.
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 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
Studio Technologies, Inc. Model 46A Interface, Issue 1, Page 3