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Model 45 User Guide Issue Preliminary 2, March 2009
Studio Technologies, Inc. Page 21
pin 2 falls below 24 volts for a continuous
1- second interval. The hardware and
software responds to this condition by
turning off the power source to pin 2 and
flashing the pin 2 LED as a warning. After
a 5-second “cool-down” interval the output
returns to the same condition as upon
initial power up. Power is again applied
to pin 2, the pin 2 status LED will light, and
monitoring won’t begin for another five sec-
onds. A full short-circuit condition applied
to the Model 45’s 2-wire connectors will
result in a continuous cycle of six seconds
on (five seconds for start up and one sec-
ond for detection) and five seconds off.
As a diagnostic aid the 2-wire (PL) power
status LED associated with pin 3 always
remains active, even when the Model 45
is supplying power to the 2-wire party-line
intercom circuit. Whenever DC in excess
of approximately 18 volts is present on
pin 3 the LED will light. This condition will
typically not exist but could prove useful
in special circumstances.
2-Wire Circuit Serves as the
Unit’s Power Source
If no external source of 24 volts DC is
connected and configuration DIP switch 1
is in its on (up) position, the connected
2-wire party-line circuit can provide power
for the Model 45. If this condition is active
the 2-wire (PL) input power LED will light.
The 2-wire (PL) power status LED will also
be lit, indicating that power in excess of
18 volts is detected on pin 2. The pin 3
LED will also light if the same condition
is present on pin 3.
Level Meters
The Model 45 contains four 5-segment LED
level meters. These meters are provided
as a support aid during installation, con-
figuration, operation, and troubleshooting.
The meters represent the strength of the
signals coming in from, and going out to,
the 4-wire connections. The meters are or-
ganized 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 sig-
nal 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
typically indicate a signal level or configu-
ration 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 incor-
rect settings on the equipment connected
to the 4-wire inputs and outputs. It’s pos-
sible that although a connected 4-wire