Studio Technologies 220 2004 - Manual (Page 13)

Issue 2, August 2004 Model 220 User Guide
Page 14 Studio Technologies, Inc.
With 4000-series IFB circuits channel 1
(XLR pin 2) provides program audio that
is “interrupted” with cue signals. This
channel is sometimes referred to as
“program-with-interrupt.” It’s important
to note that the program audio source
fully mutes whenever directors or produc-
ers are communicating with on-air talent.
Channel 2 (XLR pin 3) of the IFB circuit
provides a “program-only” audio feed.
It is never interrupted with cue signals.
While the Model 220’s IFB input was
designed for connection to a “wet” IFB
circuit, it’s also possible to connect line-
level audio sources. Please refer to the
Technical Notes section of this user guide
for details.
Line Inputs
The Model 220 allows two line-level audio
sources to be connected. These sources
can be individually routed to the left-chan-
nel, right-channel, or both the left- and
right-channel headphone outputs. The
inputs are balanced, transformer-coupled
with a nominal impedance of 10 k ohms.
Capacitors, in series with the transformer’s
input leads, prevent DC voltage that’s
present on a connected source from im-
pacting performance. The line inputs are
compatible with signals that have a nomi-
nal level of –12 dBV to +6 dBu. Two trim
potentiometers, located on the bottom of
the Model 220’s enclosure, allow 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 5.0 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,