Studio Technologies 220 2013 - Manual (Page 37)

Model 220 User Guide Issue 5, February 2013
Studio Technologies, Inc. Page 37
P17: Pin 1 is connected to the common
point of the Model 220’s circuitry. Pin 2 is
connected to the circuitry associated with
the talkback 1 button. Pin 3 is connected
to the circuitry associated with the talk-
back 2 button.
P18: Pin 1 is connected to the common
point of the Model 220’s circuitry. Pin 2 is
connected to the circuitry associated with
the main out button. Pin 3 is connected to
the circuitry associated with the auxiliary
pushbutton input. (This function is not cur-
rently supported in software.)
The input circuitry is “active low,” with a
10 k ohm resistor connected to +5 volts
acting as a pull up. A combination of resis-
tors and capacitors provide ESD protec-
tion. A qualified technician can use these
inputs for special applications. Contact
the factory for additional details.
Compressor Circuit
In this section some general information
about the Model 220’s compressor circuit
will be provided. As previously discussed,
the output of the microphone preampli-
fier circuit is connected to a studio-qual-
ity compressor circuit. The output of the
compressor is used by the talkback out-
puts and, if configured, the main output.
(In most cases the main output will utilize
the signal coming directly out of the micro-
phone preamplifier.) The gain element in
the compressor circuit is a laser-trimmed
voltage-controlled-amplifier integrated
circuit. It provides accurate, low-noise,
low-distortion performance. The threshold
of the compressor circuit is 2 dB above
the Model 220’s nominal internal operating
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 excellent
talkback audio would be provided. By
controlling the dynamic range, intelligibility
can be improved and overloading of con-
nected devices can be avoided. An LED
indicator lights whenever the compressor’s
threshold has been reached and the circuit
is actively controlling the dynamic range.
This LED is provided as an aid when setting
the gain of the microphone preamplifier.
Auxiliary Relay
The Model 220 provides an auxiliary relay
for use in specialized applications. Some
“head scratching” or “brainstorming”
should lead to a number of interesting ways
to take advantage of this unique resource.
To implement any auxiliary relay applica-
tion does require the services of a qualified
technician. This is because the Model 220’s
enclosure must be disassembled and the
desired wiring scheme implemented. The
relay operates under software control, fol-
lowing the configuration selected using two
of the DIP switches. Four operating modes
are available: relay disabled, relay follows
main output status, relay follows talkback
output 1 button status, and relay follows
talkback output 2 button status. These
choices were previously discussed in this
user guide and should be reviewed.
The relay provides two “form-C” contacts,
each consisting of a common, normally
open (not shorted), and normally closed
(shorted) connection. Obviously the two
form-C contacts change state in unison;
two independent relay functions are
not provided. These relay contacts are
accessible on the Model 220’s main
printed circuit board assembly by way
of 3-position header connectors. The con-
tacts are titled A and B, but there is no
significance between the two. The header