Studio Technologies 210 2008 - Manual (Page 27)

Model 210 User Guide Issue 4, October 2008
Studio Technologies, Inc. Page 27
and 3 of the microphone input connector.
The resistors and the power source work
together to provide 48 ±4 volts, up to a
maximum current of 10 milliamperes.
Symptoms of Insufficient
Power
A core part of the Model 210’s internal
circuitry is a switch-mode power supply
that produces +48 volts, +12 volts, +5
volts, and –12 volts. This power supply
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, 105 milliamperes for the IFB input
and 70 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 210
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 210’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 210,
maintaining the required voltage and cur-
rent is more critical. Should the voltage or
current fall below the specified minimum,
the Model 210’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 210’s IFB input, the Model 210’s
power supply will draw a steady amount
of energy. This will not disturb the analog
signals on pin 1 (common for DC and au-
dio) and pin 2 (DC and channel 1 audio).
But if the Model 210’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 situation, no damage will be done
to the Model 210’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 problem. Generally, problems will be
caused by broken or damaged connec-
tor pins, dirty patch points, or damaged
(partially open) cable conductors. Measur-
ing the IFB circuit’s voltage and current
draw directly at the Model 210’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
circuits for broadcast applications use
outdated technology that provides
mediocre performance. That’s why