Issue 1, September 2014
Model 46A User Guide
Page 8
Studio Technologies, Inc.
offering a clear view of the 2-wire DC power
and auto null functions.
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 excel-
lent 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 se-
lected 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 imped-
ance characteristics of each interface’s DC
powered (“wet”) channels was tailored to
be essentially identical to that of the un-
powered (“dry”) channel. This unique situa-
tion 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, preventing unwanted audio from
reaching the connected equipment. Asso-
ciated 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 pres-
ent on the 2-wire circuits, ensures that
audio instability associated with untermi-
nated circuits will rarely occur. As previ-
ously 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 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 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 46A’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 (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 applica-
tions, three opto-coupled inputs allow se-
lected Model 46A features to be remotely
controlled. These features include remote
auto nulling for each interface and remote
“mic kill” activation.
