Model 42A User Guide
Issue 2, December 2013
Studio Technologies, Inc.
Page 13
when typical audio signals are present.
The desired nominal output level of the
IFB outputs is –10 dBu. This is reflected
in the top green LED being calibrated
to, and labeled, –10. The meters’ yellow
LEDs, labeled –4, should light infrequently,
generally only when signal peaks are pres-
ent. Achieving a precise level calibration is
not critical. But getting the levels within the
optimum range is very important!
It’s likely that the initial levels provided by
analog ports on a digital matrix intercom
system won’t be an exact match with the
Model 42A’s audio inputs. This shouldn’t
pose a problem as the computer control
available on contemporary intercom sys-
tems should make level adjustment very
simple. From our research we found that
the Clear-Com Eclipse™ system speci-
fies a nominal level of 0 dBu. Since their
headroom is listed as greater than 18 dB,
increasing the nominal level of their ana-
log output ports by 4 dB (to achieve the
d4 dBu) should be acceptable.
RTS in their ADAM™ and ZEUS™ systems
specify nominal output levels of +8 dBu.
With these systems correct Model 42A
performance would be provided by reduc-
ing the ports’ output levels by 4 dB. With
the Artist™ system from Riedel, the analog
ports have a nominal level of +6 dBu. A
2 dB reduction in their output level would
be beneficial. In reality, a signal with a
nominal level that deviates somewhat from
pre4 dBu will be acceptable.
But with the flexibility of contemporary
computer-controlled intercom systems,
there’s no reason why a precisely calibrat-
ed system can’t be easily implemented.
Audio Integrity
At this stage the Model 42A should have
been installed and the audio source levels
adjusted as required. The unit should now
be ready for many years of excellent per-
formance. But before turning to another
task, performing a final Model 42A “real-
ity check” is highly recommended. Using
the monitor section, along with a pair of
high-quality stereo headphones, carefully
listen to each channel associated with the
four IFB outputs. Ensure that the correct
audio sources are assigned to the cor-
rect IFB outputs. Confirm that all interrupt
channels have the correct audio levels as
they switch from normal audio to interrupt
content. Overall, the audio quality should
be excellent, with no hum, noise, hiss, or
other objectionable content. Should any
issues be detected, now is the time to
correct them. Presenting users with a
correctly implemented IFB system will
make life better for everyone involved!
Operation
Overall, the Model 42A is designed for
continuous operation with no adjustment
or maintenance required. On the audio
input side, maintaining the correct level
coming from the audio sources is very
important. As for the IFB outputs, the
cabling that connects the Model 42A to
the user devices must remain free of full or
partial short circuits. And the total current
draw of the connected user devices must
remain at 220 milliamperes or less.
The audio and DC voltage monitor func-
tions will assist users in confirming that
correct operation is taking place. In addi-
tion, the under-voltage shutdown function
will help to protect the IFB output circuitry
should a fault condition be detected. The
“heart” of the monitor section is logic
circuitry created by a microcontroller
integrated circuit along with its associated
