Studio Technologies M233-01151 - Manual (Page 42)

Issue 5, November 2014 Model 233 User Guide
Page 42 Studio Technologies, Inc.
Remote Control/Tally
Connections
Provision has been made on the Model
233’s printed circuit board assembly to
allow external switches or contact closures
to control the main output and talkback
button functions. In addition, a DC “tally”
output signal provides an indication of the
status of the main output. Two 3-position
headers provide access to the circuitry
associated with these functions.
P18: Remote Talkback Switch Inputs,
pin 1 is connected to the common point
of the Model 233’s circuitry. Pin 2 is con-
nected to the circuitry associated with the
talkback 1 button. Pin 3 is connected to
the circuitry associated with the talkback 2
button.
P19: Remote Main Switch Input/Tally
Output, pin 1 is connected to the common
point of the Model 233’s circuitry. Pin 2 is
connected to the circuitry associated with
the main output pushbutton. Pin 3 is con-
nected to circuitry associated with the tally
output.
The remote switch input circuits are
“active low,” with a 10 k ohm resistor
connected to +5 volts acting as a pull up.
A combination of resistors and capacitors
provide ESD protection. The tally output
is nominally 3.5 volts DC and is current
limited to 12 milliamperes. This output
can directly drive LED indicators. Using
a series resistor in the range of 150 to
330 ohms is recommended. This will limit
the current while still providing adequate
LED light output.
Compressor Circuit
In this section some general information
about the Model 233’s compressor
circuit will be provided. As previously
discussed, the output of the microphone
preamplifier circuit is connected to a
studio-quality compressor circuit. The
output of the compressor is used by the
talkback functions and, if configured, the
main output. (In most cases the main
output will utilize the signal coming directly
out of the microphone preamplifier.) The
gain element in the compressor circuit is
a laser-trimmed voltage-controlled-ampli-
fier integrated circuit. It provides accurate,
low-noise, low-distortion performance. The
threshold of the compressor circuit is 2 dB
above the Model 233’s nominal internal op-
erating level of –2 dBu. A 5:1 compression
ratio is implemented and, like the threshold
level, is not field adjustable. The threshold
and ratio settings were selected so that ex-
cellent talkback audio would be provided.
By controlling the dynamic range, intel-
ligibility can be improved and overloading
of connected devices can be avoided. An
LED indicator lights whenever the com-
pressor’s threshold has been reached and
the circuit is actively controlling the dynam-
ic range. This LED is provided as an aid
when setting the gain of the microphone
preamplifier.
Auxiliary Relay
The Model 233 provides an auxiliary re-
lay for use in specialized applications.
Some “head scratching” or “brainstorm-
ing” should lead to a number of interest-
ing ways to take advantage of this unique
resource. To implement any auxiliary relay
application does require the services of a
qualified technician. This is because the
Model 233’s enclosure must be disas-
sembled and the desired wiring scheme
implemented. The relay operates under
software control, following the configura-
tion selected using two of the DIP switches.