Studio Technologies 47A - Manual (Page 8)

Issue 1, September 2014 Model 47A User Guide
Page 8 Studio Technologies, Inc.
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, offering a clear view
of the 2-wire DC power and auto null
functions.
Pro Audio Quality
The Model 47A’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 headroom. Using passive
and active filters, the frequency response
is limited to approximately 100 Hz to 8 kHz.
This range was selected to provide excel-
lent 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 se-
lected 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,
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 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 di-
rectly 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 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 al-
low 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 pushbutton switches oper-
ate. 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 inde-
pendently. 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 inter-
face and remote “mic kill” activation.