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Issue 1, September 2007 Model 233 User Guide
Page 16 Studio Technologies, Inc.
intercom channels. In addition, the inter-
com line can provide the DC power re-
quired to operate the Model 233’s circuitry.
An intercom line is connected to the
Model 233 by way of a 3-pin female XLR-
type connector which is located on the
back panel. The mating connector (male)
should be wired so that common is on
pin 1, DC with channel 1 audio is on pin
2, and channel 2 audio is on pin 3. With
single-channel intercom lines common is
on pin 1, DC power is on pin 2, and audio
is connected to pin 3.
The Model 233’s intercom interface is
directly compatible with broadcast and
production party-line intercom lines as-
sociated with systems from manufactures
such as RTS and Clear-Com. Intercom
lines associated with other systems
should be equally compatible. RTS TW
series systems are normally interfaced
using 3-pin XLR-type connectors. These
connectors are wired with common on
pin 1, DC power and channel 1 audio on
pin 2, and channel 2 audio on pin 3. With
many Clear-Com systems, common is on
pin 1, DC power is provided on pin 2, and
audio is provided on pin 3.
The DC power supplied by the connected
intercom line is generally sufficient to
operate the Model 233’s circuitry. The
acceptable input range is 24 to 32 volts,
with a required current of 125 milliam-
peres. Note that the specified input volt-
age is given when measured directly at
the Model 233’s intercom input connec-
tor (with the connector terminated on the
Model 233) and not at the source of the
intercom system’s power.
External Power Input
An external source of 24 volt DC power can
be connected to the Model 233 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 233 requires
90 milliamperes at 24 volts DC for correct
operation. Included with each Model 233
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 233’s
24 Vdc input jack. The locking feature is im-
portant, allowing the external power source
to be securely attached to the Model 233.
As previously discussed in this user guide,
an intercom line connected to the Model
233 can serve as the unit’s power source.
Alternately, an external 24 volt DC source
can be connected. For redundancy, the in-
tercom line and the external source can be
connected at the same time. If one of them
becomes inoperative the remaining source
will provide power for the Model 233.
The Model 233’s circuitry establishes the
priority in which the unit draws its operating
power. If an external source of 24 volt DC
power is connected, it will always serve as
the primary source. This minimizes the im-
pact that the unit’s power draw could have
on a connected intercom line. If no external
source of 24 volt DC is connected then
power will be drawn from the intercom line.
And, of course, no matter which source is
providing power full operation of the inter-
com interface can take place.