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Issue 1, September 2007 Model 233 User Guide
Page 10 Studio Technologies, Inc.
Intercom Interface
Of special note is the Model 233’s sophisti-
cated intercom interface. It’s designed
to work correctly with industry-standard
single- and dual-channel party-line inter-
com systems, including those from RTS
and Clear-Com. An intercom line connect-
ed to the Model 233 can serve three func-
tions: providing cue audio signals to the
headphone output, allowing talkback audio
to be sent to intercom users, and acting
as a Model 233 power source. Audio sig-
nals present on the single- or dual-channel
intercom line can be flexibly routed to the
stereo headphone output. Talkback audio,
controlled by the two talkback pushbutton
switches, can be sent to either or both of
the intercom channels. Trim potentiom-
eters, located on the bottom of the unit, al-
low adjustment of the talkback-to-intercom
sidetone (null) level.
Other announcer console products can
exhibit talkback-to-intercom-related audio
oscillations (“squeals”) that end up in the
headphone output. A unique Model 233
feature ensures that this will never occur.
This is accomplished by means of a special
“auto-terminate” circuit that becomes active
whenever an intercom line is not connected
to the Model 233.
Audio Quality and Protection
The Model 233’s circuitry is carefully
tailored to provide excellent audio perfor-
mance. Professional-quality components
are featured throughout. For reliability all
audio routing is performed using solid-state
devices under microcontroller direction. In
all critical audio paths, “clickless” electronic
switches provide noise-free control. All
audio inputs and outputs make extensive
use of protection components. This limits
the chance of damage from ESD and other
undesirable, yet real-world, hazards.
Power Sources
The Model 233 can derive its operating
power from an intercom line or an external
24 volt DC source. For redundancy, both
power sources can be connected simul-
taneously. An internal switch-mode power
supply ensures that all Model 233 features
are available, including phantom power,
when the unit is powered by either source.
Auxiliary Relay
Model 233 resources include a general-
purpose relay, allowing specialized configu-
rations to be created. Under software con-
trol, the relay can be configured to follow
the state of the main output, talkback 1,
or talkback 2 buttons. Taking advantage
of the back-panel locations provided for
additional XLR-type connectors, a techni-
cian may easily create functions such as
an “on-air” indicator or implement a loud-
speaker muting during talkback function.
Special configuration modes are even
included to allow direct control of the relay
using the talkback 1 or talkback 2 buttons
without impacting any of the Model 233’s
audio signals.
Tally Output
Another unique Model 233 feature is the
tally output. It provides an indication, in
the form of a current-limited DC signal,
of the status of the main output. Whenever
the main output is active the tally output
is active. This 3.5 volt nominal, 12 milliam-
peres maximum, signal is capable of di-
rectly lighting an LED indicator or triggering
an external control system. The tally output
is provided specifically for specialized ap-
plications such as television award show
broadcasts where remote monitoring and
control of the main output is required.