Studio Technologies 5120 2011 - Manual (Page 10)

Issue 3, November 2011 Model 5120 User Guide
Page 10 Studio Technologies, Inc.
Model 5120
Line/IFB Output Module
The line output circuitry is protected from
damage should a moderate DC voltage be
applied. For example, no damage will occur
if a Model 5120’s IFB output (28 volts DC)
is accidentally connected. This protection
would also be effective should a party-line
intercom circuit or microphone phantom
power signal be accidentally connected.
IFB Output
One or more listen-only broadcast-standard
IFB devices can be connected to the IFB
output. The only restriction on the number
of units that can be connected is that the
total current draw must be equal to or less
than 120 milliamperes. Devices such as
the Studio Technologies’ Models 32A,
33A, or 34 are directly compatible and will
provide excellent performance. While not
cost-effective, it’s also possible to con-
nect intercom beltpacks such as the RTS®
BP325 as listen-only devices.
An interesting Model 5120 characteristic
is that its IFB output maintains a 200 ohm
impedance on both pin 2 and pin 3. This
effectively creates a low-current party-line
intercom power supply. With this capability
two BP325 beltpacks connected to a Model
5120 IFB output cannot only listen to the
IFB signals but also communicate between
themselves; a very small party line indeed,
but possibly a useful one too.
To clarify, the signals that are present on
the IFB output’s 3-pin male XLR connector:
pin 1 is power and audio common; pin 2 is
28 volts DC with channel 1 audio modulated
on it; pin 3 is channel 2 audio. The nominal
audio output level on the IFB output chan-
nels is –10 dBu, no matter if the module
is a 5120S or a 5120E. The maximum
current draw from pin 2 to pin 1 is 120
milliamperes. The circuitry associated with
pin 3 is protected from damage should pin
2 (nominal 28 volts DC) be connected to it.
DC Voltage Monitoring
The Model 5120’s microcontroller inte-
grated circuit, under software control,
“watches” to ensure that the DC voltage
present on pin 2 of the IFB output is at an
acceptable level. The low-voltage threshold
for the Model 5120’s nominal 28 volt DC
output is 24 volts. The DC Pin 2 status LED
provides an indication of the DC voltage
on the IFB output’s XLR connector. The
LED will “flash” at a moderate cadence if
the voltage on the IFB circuit falls below
the acceptable value. This can be caused
by a temporary over-current or short-circuit
condition, such as when interconnecting
user devices to the IFB circuit using por-
table cabling.
An under-voltage condition that’s pres-
ent for a continuous 1-second period will
cause a fault condition to be recognized.
The status LED will indicate this condition
by flashing at a faster rate. In addition, the
output voltage on the IFB circuit will auto-
matically shut down to an essentially off
condition. A 5-second “cool-down” period
will then take place, after which the output
voltage will again become active. As soon
as the output is enabled normal output
voltage monitoring will again take place.
A continuous short-circuit presented to
the IFB output will result in a continuous
4-seconds-on, 5-seconds-off error cycle.
It’s important to note that during the
5-seconds-off period no voltage monitoring
takes places. Removing the fault condition
will not result in the output voltage immedi-
ately turning on again; the 5-second shut-
down period must first elapse.