Studio Technologies 220 2013 - Manual (Page 14)

Issue 5, February 2013 Model 220 User Guide
Page 14 Studio Technologies, Inc.
only have one audio channel. In this case,
audio will generally be on pin 3 with pin 2
providing only DC power.
The power supplied by an IFB circuit,
normally in the range of 28 to 32 volts DC,
is usually sufficient to operate the Model
220’s circuitry. The acceptable input range
is 24 to 32 volts, with a required current
of 125 milliamperes. Note that the speci-
fied input voltage is given when measured
directly at the Model 220’s IFB input con-
nector, not at the source of the IFB circuit.
The one or two audio signals provided
by the IFB circuit can serve as the audio
sources for the headphone outputs.
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 con-
nected to the line inputs by way of 3-pin
female XLR 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 elimi-
nate the issue. With an unbalanced 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 re-
sults 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 requirement 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 Switchcraft® S760K
coaxial power plug. This “locking” type of
plug correctly mates with the Model 220’s
24 Vdc input jack. The locking feature is im-
portant, 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 redundancy,
both the IFB circuit and the external source
can be connected at the same time. If
one or the other becomes inoperative,
the remaining source will provide all
Model 220 power.