Studio Technologies 220 2004 - Manual (Page 31)

Issue 2, August 2004 Model 220 User Guide
Page 32 Studio Technologies, Inc.
circuit works very well as long as it is “fed”
with sufficient input voltage and current.
“Sufficient” is defined as a minimum of 24
volts on the IFB input and 20 volts on the
external 24 volt DC input. The necessary
current, 125 milliamperes for the IFB input
and 80 milliamperes for the external input,
must be supplied over their respective
voltage ranges.
It’s worth discussing what will happen
if either power source falls below its speci-
fied minimum. Typically, if the Model 220
is being powered by an external 24 volt
nominal power source, normal operation
will continue until the input falls to the
18-20 volt range. As the input voltage
drops below this range the Model 220’s
internal power supply will have reduced
stability, operating in this manner until its
low-voltage shutdown circuit halts opera-
tion. Note that as the input voltage moves
down from 24 volts the input current will
rise proportionately to make up for the
loss of power.
If an IFB circuit is powering the Model 220,
maintaining the required voltage and cur-
rent is more critical. Should the voltage or
current fall below the specified minimum,
the Model 220’s power supply circuit will
again become unstable. This will become
an issue as noise will be induced into
the IFB circuit’s audio signals. The reason
is simple: an IFB circuit “multiplexes”
3-conductors so that they carry both pow-
er and audio signals. If sufficient amounts
of voltage and current are supplied to the
Model 220’s IFB input, the Model 220’s
power supply will draw a steady amount
of energy. This will not disturb the analog
signals on pin 1 (common for DC and
audio) and pin 2 (DC and channel 1 au-
dio). But if the Model 220’s power supply
is not supplied with sufficient energy (volts
x amps) it will try to draw what it needs from
the IFB circuit, becoming unstable in the
process. The IFB circuit’s audio signals will
be corrupted by the power supply’s attempt
to draw enough power. Instead of nice
clean audio there will be squeaks, squeals,
and some awfully funky noises added.
Again, in a low-voltage or low-current situa-
tion, no damage will be done to the Model
220’s circuitry but correct operation will not
be possible.
In most cases maintaining the IFB circuit’s
required voltage and current shouldn’t
be a problem. But issues may arise due
to malfunctioning IFB circuit sources or
poor interconnect cabling. Typically, ex-
cessive cable length won’t be the cause
of a problem. Generally, problems will be
caused by broken or damaged connector
pins, dirty patch points, or damaged
(partially open) cable conductors. Measur-
ing the IFB circuit’s voltage and current
draw directly at the Model 220’s IFB input
connector will quickly identify if there’s a
power issue.
And now for another shameless “plug”
for other Studio Technologies products:
Frankly, most devices that supply IFB cir-
cuits for broadcast applications use out-
dated technology that provides mediocre
performance. That’s why Studio Tech-
nologies’ developed high-performance IFB
interface units. These products do an excel-
lent job of providing power and audio to
connected devices such as the Model 220.
However, unlike other products, the power
supplied by these units’ IFB circuits main-
tain their output voltage all the way to their
full rated current. The result is being able to
power more devices over longer cable runs.
In addition, the audio quality of these units
is superior. For further information please
refer to the Studio Technologies website.