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Issue 2, September 2007 Model 46 User Guide
Page 8 Studio Technologies, Inc.
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 46’s audio circuitry was de-
signed 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 head-
room. Using passive and active filters, the
frequency response is limited to approxi-
mately 100 Hz to 8 kHz. This range was se-
lected to provide excellent performance for
human speech, while maximizing the ability
of the hybrids to create substantial “nulls.”
When the Model 46’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 addi-
tion, 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 null-
ing circuitry to provide excellent, consistent
results for both the powered and unpow-
ered channels.
Attention to detail is a hallmark of the Model
46’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 termi-
nating 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 instabil-
ity associated with unterminated circuits
will rarely occur. As previously mentioned
the Model 46’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 46 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 dis-
able it. This would allow full control over
the Model 46’s four hybrid circuits, en-
abling them to be used completely inde-
pendently. 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 alter-
nate 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 46 features
to be remotely controlled. These features
include remote auto nulling for each inter-
face and remote “mic kill” activation.