Studio Technologies 5120 2014 - Manual (Page 10)

Issue 5, October 2014 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
P48 phantom power signal be accidentally
connected.
IFB Output
One or more listen-only broadcast-stan-
dard 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 connect 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 Mod-
el 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/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.