Studio Technologies 47A - Manual (Page 20)

Issue 1, September 2014 Model 47A User Guide
Page 20 Studio Technologies, Inc.
Operation
Technician intervention is typically not
required during normal Model 47A opera-
tion. The unit is designed for continuous
operation with no routine maintenance
necessary. Activating the auto null func-
tions may be warranted should connected
user devices or wiring associated with the
2-wire party-line intercom be changed.
Upon power-up the Model 47A will go
through a short initialization sequence
before normal operation will begin. The
power and status LEDs will each light
sequentially and, upon completion, the
power LED will light steadily. The settings
for the four hybrid circuits are stored in
non-volatile memory and will be recalled
during the power-up process.
Level Meters
The Model 47A contains eight 5-segment
LED level meters. These meters are pro-
vided as a support aid during installation,
configuration, operation, and troubleshoot-
ing. The meters represent the signals com-
ing in from, and going out to, the 4-wire
connections. The meters are organized in
four groups each representing one input
and one output. They are calibrated to
reflect the level in dB relative to the config-
ured nominal operating level. This is similar
to the way in which now-legacy VU meters
functioned. As an example let’s take the
situation where the nominal operating level
of interface 1 is configured for +4 dBu. The
LEDs labeled –18, –12, –6, and 0 of the TO
4-wire ch 1 meters are lit. (For this exam-
ple, the level on pin 2 of interface 1’s 2-wire
PL circuit is just large enough to light the
0 LED.) This indicates that a signal with the
approximate level of +4 dBu is present on
the associated 4-wire output connector.
Another example would be a Model 47A
interface configured for +8 dBu opera-
tion and –18 and –12 dB LEDs are lit. This
would indicate that a signal with an audio
level of approximately –4 dBu is present on
its associated output.
Each level meter contains four green LEDs
and one yellow LED. The four green LEDs
indicate signal levels at or below the con-
figured nominal level. The top LED is yel-
low in color and indicates a signal that is
6 dB or greater than the nominal level.
An audio signal that causes the yellow LED
to light doesn’t necessarily indicate an ex-
cessive level condition, but it does provide
a warning that at some point reducing the
signal level may be prudent. Operation with
normal signal levels should find the meters
lighting near their 0-dB point. Signal peaks
may cause the yellow LEDs to flash. But a
yellow LED that lights fully during normal
operation will typically indicate a signal
level or configuration problem.
If the FROM 4-wire meters display consis-
tency lower or higher levels than their 0-dB
points it’s possible that a configuration
issue exists. One potential problem is in-
correctly set 4-wire nominal audio level
DIP switches for one or both of the Model
47A’s interfaces. If the nominal level is set
too low then sufficient audio headroom
might not be available. It can also result
Figure 9. DIP Switch 4—Factory Test