Studio Technologies 42A 2008 - Manual (Page 14)

Issue 1, February 2008 Model 42A User Guide
Page 14 Studio Technologies, Inc.
audio source adjusted as required. The
unit should now be ready for many years
of excellent performance. But before
turning to another task, performing a final
Model 42A “reality check” is highly rec-
ommended. Using the monitor section,
along with a pair of high-quality stereo
headphones, carefully listen to each chan-
nel associated with the four IFB circuits.
Ensure that the correct audio sources are
assigned to the correct IFB circuits. Con-
firm 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 work them out. Present-
ing IFB circuit users with a correctly imple-
mented 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 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 devic-
es must remain free of full or partial short
circuits. And the total current draw of the
connected user devices must remain at
200 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 shut-down function
will help to protect the IFB output circuitry
and connected user devices 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 firmware. This
combination adds “smarts” to otherwise
fairly pedestrian functions.
Using four electromechanical relays, the
audio monitor section accesses the IFB
circuits directly on pins 2 and 3 of the
output connectors. This ensures that the
impact of the actual wiring and connected
user devices is monitored, rather than just
observing something internal to the Model
42A’s circuitry. Pin 2 of each pair of the
IFB output connectors (one connector on
the front panel and one on the back) is
also connected, by way of interface circuit-
ry, to analog-to-digital converter inputs on
the processor. This allows the DC output
voltages to be continuously monitored.
Associated with the audio and DC voltage
monitor functions are four status LEDs,
one pushbutton switch, two 5-segment
LED level meters, a rotary level control,
and a headphone jack. The four monitor
status LEDs are used to indicate which
IFB circuit is currently being audio moni-
tored as well as presenting the status of
the DC output voltages. One of the LEDs
is always lit, indicating which IFB circuit is
currently being monitored by the meters
and headphone output.
Figure 7. Detail of front panel showing four
status LEDs and associated pushbutton switch