Studio Technologies 5121 - Manual (Page 12)

Issue 3, October 2014 Model 5121 User Guide
Page 12 Studio Technologies, Inc.
Model 5121
Line/IFB Output Module
digital input or one of the analog inputs. The
ability to adjust the audio level can be use-
ful when the sources being supplied to the
Model 5121 are not optimal for the applica-
tion. For example, users of the line-level or
IFB outputs may need additional gain to
clearly hear their talent cues.
The Model 5121’s gain values can only be
viewed and adjusted using a Model 5190
Remote Access Module. But the actual
values are stored in non-volatile memory
that is part of the Model 5121’s circuitry.
Upon power up the Model 5121 will always
use these stored gain values, whether or not
a Model 5190 is currently connected and
communicating.
The data LED, located on the Model 5121’s
front panel, will light whenever data activity
is taking place over the local RS-485 signal
bus that is used to link the Model 5121 to a
Model 5190 Remote Access Module. The
LED will flash on and off each time data
associated with this specific Model 5121 is
present. Not all applications will include a
connection to the data bus so it’s certainly
possible that the data LED may never flash
except during module power up.
Technical Notes
Maintaining Correct Input
Signal Levels
The Model 5121’s two audio inputs are
designed for either SMPTE (5121S) or EBU
(5121E) audio level compatibility. Apply-
ing 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. Applying signal
levels significantly higher than nominal will
reduce the headroom and greatly increase
the chance of reaching audio “clipping.” Ob-
viously, these cautions are not unique to the
Model 5121, but apply to most audio equip-
ment. The front-panel level meters provide
an easy means of confirming that a Model
5121 is being presented with the correct
audio levels.
For the Model 5121S the nominal input
signal level is +4 dBu for an analog source
and –20 dBFS for a digital source. For
the Model 5121E the nominal input level is
0 dBu for analog and –18 dBFS for digital.
The analog output level for nominal level
input signals is +4 dBU for the Model 5121S
and 0 dBu for the Model 5121E. 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 5121
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 5121’s IFB output is designed to
provide up to 120 milliamperes of DC cur-
rent. By design, the IFB circuit is protected
so that an overload condition, or even a
complete short circuit, should not cause