Manual

Issue 3, August 2015 Model 45A User Guide
Page 22 Studio Technologies, Inc.
lit, indicating that power in excess of 20
volts is detected on pin 2. The pin 3 LED
will also light if the same condition is pres-
ent on pin 3.
Level Meters
The Model 45A contains four 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 strength of
the signals coming in from, and going out
to, the 4-wire connections. The meters are
organized in two groups each representing
one input and one output. They are cali-
brated to reflect the level in dB relative to
+4 dBu. This is similar to the way in which
now-legacy VU meters functioned. As an
example let’s take the situation where an
output (“to 4-wire”) LED labeled 0 dB is lit.
(For this example, the level on the 2-wire
party-line circuit is just large enough to light
the 0 LED.) This indicates that a signal with
an approximate level of +4 dBu is present
on the associated 4-wire output connector.
Each level meter contains four green LEDs
and one yellow LED. The four green LEDs
indicate signal levels at or below +4 dBu.
The top LED is yellow and indicates a sig-
nal that is 6 dB or greater than the +4 dBu
nominal level. An audio signal that causes
the yellow LED to light doesn’t necessarily
indicate an excessive level condition, but it
does provide a warning that at some stage
reducing the signal level may be prudent.
Typical 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 typi-
cally indicate a signal level or configuration
problem.
If the meters consistently display lower
or higher levels than their 0 dB points it’s
possible that a configuration issue exists.
This would typically be related to incorrect
settings on the equipment connected to
the 4-wire inputs and outputs. It’s possible
that although a connected 4-wire device’s
nominal level matches the Model 45A’s
level setting its actual nominal level may be
significantly different. With a digital matrix
intercom system this problem could be
due to an incorrect configuration having
been made to a specific channel or port.
For example, the RTS ADAM system has
a published nominal level of +8 dBu, but
using its configuration software it’s possible
to set panels or ports to a level different
than nominal. The best solution in this case
is to adjust the associated port on the inter-
com system so that its levels comply with
+4 dBu. This should, at least in theory, lead
to the best system performance, including
correct interfacing with the Model 45A. But
often it’s impossible to “clean up” the levels
of an existing system.
The “to” 4-wire meters display the level
of signals that come from the 2-wire party-
line circuit and go out the 4-wire interfaces.
An issue may arise if the signals coming
from the connected party-line user devices
aren’t at a sufficient level so that a normal
meter display can be reached. This could
be the result of an incorrectly configured
2-wire nominal audio level.
It’s also possible that an error is present
on the 2-wire party-line circuit. Signal levels
associated with 2-wire party-line circuits
depend on a single termination being pres-
ent. This termination, typically 200 ohms,
is almost always made at the power supply
source. But it’s possible that another de-
vice, such as a second active power supply