Studio Technologies 240 - Manual (Page 27)

Model 240 User Guide Issue 1, August 2013
Studio Technologies, Inc. Page 27
main output audio can be effectively sent
to the IFB circuit due to its one-way nature.
(Technically, a powered IFB circuit has a
low-source-impedance and a high-input-
impedance circuit arrangement.)
The power supplied by an IFB circuit, nor-
mally in the range of 28 to 32 volts DC, is
usually sufficient to operate the Model 240’s
circuitry. The acceptable input range is 24
to 32 volts, with a required current of 150
milliamperes. Note that the specified input
voltage is given when measured directly at
the Model 240’s intercom interface connec-
tor, not at the source of the IFB circuit.
In North American field and in-studio broad-
cast applications it is possible to find RTS
4000-series IFB equipment being used to
provide the IFB circuits. The Model 240 can
be directly connected to, and function cor-
rectly with, one of these circuits. For reliable
operation, especially when using lengthy
cable runs, it’s strongly recommended that
no other device be connected to a 4000-
series IFB circuit that is specified for con-
nection to a Model 240. This requirement
is due to the current-limited DC source that
is supplied by the 4010 IFB Controller.
Symptoms of Insufficient
Power
A core part of the Model 240’s internal
circuitry is a switch-mode power supply
that produces +12 volts, +5 volts, and
–12 volts. This power supply circuit works
very well as long as it is “fed” with suffi-
cient input voltage and current. “Sufficient”
is defined as a minimum of 24 volts on
the intercom interface and 20 volts on the
external 24 volt DC input. The necessary
current, 150 milliamperes for the intercom
circuit and 125 milliamperes for the external
source, must be supplied over their respec-
tive voltage ranges.
It’s worth discussing what will happen if
either of these power sources fall below
their specified minimum. Typically, if the
Model 240 is being powered by an external
24 volt nominal power source, normal oper-
ation will continue until the input falls to the
18-20 volt range. As the input voltage drops
below this range the Model 240’s internal
power supply will have reduced stability,
operating in this manner until its low-voltage
shutdown circuit halts operation. Note that
as the input voltage moves down from 24
volts the input current will rise proportion-
ately to make up for the loss of power.
Using the intercom circuit to provide Model
240 power shouldn’t prove to be a problem.
Power supplies associated with broadcast
and production intercom systems are de-
signed to support multiple beltpack and re-
lated devices. In the “big scheme of things,”
connecting a Model 240 shouldn’t add a
significant load.
Travel Case
For portable applications it may be desir-
able to store and transport each Model 240
in a protective case. After much travel with
prototype units, Studio Technologies per-
sonnel learned to appreciate the Pelican
Model 1450 case. Purchased with the foam
interior option, it does an excellent job of
holding one Model 240, its associated 24
volt DC power supply, and documentation.
Some applications may benefit from select-
ing a larger case that would also hold a
related headset, cables, etc. A larger case
could also be selected that would hold
multiple Model 240 units. Pelican sells their
products through a dealer network, many
of which can be located via a web search.
Spare Connector Locations
Four spare connector locations are pro-
vided on the Model 240’s back panel. From