Studio Technologies 5120 2011 - Manual (Page 11)

Model 5120 User Guide Issue 3, November 2011
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 de-
signed 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 ap-
ply to most audio equipment. The front-
panel level meters provide an easy means
of confirming that a Model 5120 is being
presented 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 digi-
tal. The analog output level for nominal
level input 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 information
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 protect-
ed so that an overload condition, or even
a complete short circuit, should not cause
damage. Exceeding 120 milliamperes for
more than one second will cause the auto
shut-down mode to become active. A con-
tinuous 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 extreme
cases, such as where the Model 5120 is
located in an environment with elevated
temperatures, a few minutes may be re-
quired from the time an overload condition
is removed to when normal operation will
again take place. Please don’t test the Mod-
el 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. Techni-
cally the LED, under software control, pro-
vides 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.