Studio Technologies 5120 2014 - Manual (Page 11)

Model 5120 User Guide Issue 5, October 2014
Studio Technologies, Inc. Page 11
Model 5120
Line/IFB Output Module
Technical Notes
Maintaining Correct Input
Signal Levels
The Model 5120’s two audio inputs are
designed for either SMPTE (5120S) or EBU
(5120E) audio level compatibility. Applying
signal levels significantly lower than the
intended nominal will reduce the signal-
to-noise ratio (raising the perceived noise
floor) and can prevent the connected user
devices from operating optimally. Apply-
ing signal levels significantly higher than
nominal will reduce the headroom and
greatly increase the chance of reaching
audio “clipping.” Obviously, these cautions
are not unique to the Model 5120, but apply
to most audio equipment. The front-panel
level meters provide an easy means of
confirming that a Model 5120 is being pre-
sented with the correct audio levels.
For the Model 5120S the nominal input
signal level is +4 dBu for an analog source
and –20 dBFS for a digital source. For the
Model 5120E the nominal input level is
0 dBu for analog and –18 dBFS for digital.
The analog output level for nominal level in-
put signals is +4 dBU for the Model 5120S
and 0 dBu for the Model 5120E. For both
versions the nominal output level of the two
channels associated with the IFB output is
–10 dBu. (Of course pin 2 on the IFB output
has both DC and audio present on it.)
To confirm correct IFB circuit operation at
locations away from where the Model 5120
is installed, it’s possible to use the Model
72 Level Meter/Interface, also available
from Studio Technologies. The Model 72
is a compact, portable device that plugs
directly into an IFB or intercom circuit
and provides two useful functions. Two
5-segment LED meters display the audio
levels present on pins 2 and 3. In addition,
“dry” line-level audio outputs are provided,
one for each channel. Complete informa-
tion on the Model 72 is available on the
Studio Technologies website.
Maintaining Correct IFB
Circuit Current Draw
The Model 5120’s IFB output is designed
to provide up to 120 milliamperes of DC
current. By design, the IFB circuit is pro-
tected so that an overload condition, or
even a complete short circuit, should not
cause damage. Exceeding 120 milliam-
peres for more than one second will cause
the auto shut-down mode to become ac-
tive. A continuous overload condition will
cause the output voltage to cycle through
a 1-second-on, 5-seconds-off sequence.
Restoring the output load to be within the
rated 120 milliamperes will allow the IFB
output to again operate normally. In ex-
treme cases, such as where the Model
5120 is located in an environment with
elevated temperatures, a few minutes may
be required from the time an overload con-
dition is removed to when normal opera-
tion will again take place. Please don’t test
the Model 5120’s ability to sustain frequent
overload or short-circuit conditions! The
long-term reliability of the unit can be
impacted by the stresses caused by these
fault conditions.
The DC Pin 2 status LED makes it simple
to know if an excessive load, or a short
circuit, is being placed on the IFB circuit.
Technically the LED, under software con-
trol, provides a direct indication of the IFB
circuit’s DC output voltage. And the output
voltage is directly related to the amount of
current being drawn.