Studio Technologies 220 2008 - Manual (Page 15)

Model 220 User Guide Issue 4, October 2008
Studio Technologies, Inc. Page 15
signals over this wide nominal level range
to be effectively utilized. Audio sources
are connected to the line inputs by way of
3-pin female XLR-type connectors which
are located on the unit’s back panel.
Prepare the mating connectors (males)
so that pin 2 is signal high (+ or hot),
pin 3 is low (– or cold), and pin 1 is shield.
If connecting a source in this manner
results in hum or noise, it’s possible that
removing the shield connection from pin
1 can eliminate the issue. With an unbal-
anced source connect pin 2 to signal high
(+ or hot) and both pins 1 and 3 to shield.
If connecting an unbalanced source in this
manner results in hum or noise, connect
pin 2 to high (+ or hot) and pin 3 to shield;
leave pin 1 unterminated.
External Power Input
An external source of 24 volt DC power
can be connected to the Model 220 by
way of a 2.1 x 5.5 mm coaxial power jack
which is located on the back panel of
the unit. The center pin of the jack is the
positive (+) connection. While the require-
ment for the external source is nominally
24 volts, correct operation will take place
over a 20 to 30 volt range. The Model 220
requires 80 milliamperes at 24 volts DC
for correct operation. Included with each
Model 220 is a 24 volt DC external power
supply. The power supply’s DC output
cable has been terminated with a Switch-
craft® S760K coaxial power plug. This
“locking” type of plug correctly mates
with the Model 220’s 24 Vdc input jack.
The locking feature is important, allowing
the external power source to be securely
attached to the Model 220.
As previously discussed in this user guide,
an IFB circuit connected to the IFB in-
put can serve as the Model 220’s power
source. Alternately, an external 24 volt
DC source can be connected. For redun-
dancy, both the IFB circuit and the exter-
nal source can be connected at the same
time. If one or the other becomes inopera-
tive, the remaining source will provide all
Model 220 power.
Note that if both an IFB circuit and an
external 24 volt DC source are connected,
power will be drawn only from the exter-
nal source. This minimizes the chance
that lengthy cable runs or other IFB circuit
issues will impact Model 220 operation.
Whichever device is providing power,
audio signals from the IFB circuit can still
serve as the audio sources for the head-
phone output.
Pushbutton Labeling
The three pushbutton switches used in
the Model 220 were selected for several
reasons. Foremost was the fact that they
are highly reliable, using gold-plated con-
tacts for long life in less-than-ideal environ-
ments. A second reason was that applying
customized labels to the button caps
would be very simple. The labels, text
printed on clear material, are placed under
the clear caps on the top of the buttons.
From the factory the left button is labeled
COUGH, the center button is labeled
TALKBACK 1, and the right button is
labeled TALKBACK 2. This was selected
to be appropriate for many on-air applica-
tions in English-speaking locations. But
it’s expected that these may need to be
changed to meet the needs of specific
applications.
As a “head start” for some applications,
a clear sheet with a number of commonly
used button designations printed on it
is included in the shipping carton. These