Studio Technologies 45DR - Manual (Page 17)

Model 45DR User Guide Issue 2, January 2015
Studio Technologies, Inc. Page 17
simple, only requiring the audio null push-
button switch to be pressed and held for
two seconds. The mode will change and
the local power LED will display accord-
ingly. The button can then be released. The
selected operating mode will be stored in
non-volatile memory so that it will restore
after a power-down/power-up cycle.
Local Power Mode Operation
When the local power LED is lit the Model
45DR provides party-line power and 200
ohm termination impedances to create a
2-channel party-line circuit. The party-line
interface supplies 29 volts DC on pin 2
of the 3-pin XLR connectors. A maximum
current draw of 240 mA is available. This
current is sufficient to power various inter-
com user devices such as small user sta-
tions and beltpacks. A common broadcast
application may use RTS BP-325 beltpacks.
Select the connected devices so that their
total maximum current doesn’t exceed
240 mA. That’s not always the easiest
figure to calculate but a web search will
generally find specifications for all com-
monly used devices. For example, a search
finds that the original version of the BP-325
consumes a maximum of 85 mA of current.
According to this figure one or two of these
units can be connected to a Model 45DR.
Newer versions of the BP-325 use surface-
mount component technology and have
a lower maximum current draw of 65 mA.
Up to three of these “modern” BP-325 units
can easily be supported.
The active LED will light when a minimal
amount of current is flowing from the
Model 45DR to the connected user device
or devices. This current, approximately
5 mA, provides a “circuit-active” signal to
the Model 45DR’s firmware, indicating that
normal operation is taking place. This helps
to prevent unwanted audio signals from
passing to and from the Dante audio
channels when no party-line devices
are connected.
The Model 45DR’s party-line intercom
power supply circuit operates under firm-
ware control. This allows detection of fault
conditions and protection of the Model
45DR’s circuitry. Upon initial Model 45DR
party-line intercom power up no monitoring
of the intercom power output takes place
for three seconds. This allows the Model
45DR’s circuitry and the connected inter-
com user devices to stabilize. The active
LED, which monitors the DC voltage on pin
2 of the 3-pin XLR connectors, will light to
indicate that the output is active. After this
initial delay period monitoring becomes
active. A fault condition is detected if the
voltage on pin 2 falls below 24 for a con-
tinuous 1-second interval. The hardware
and firmware responds to this condition by
turning off the power source to pin 2 and
flashing the active LED as a warning. After
a 5-second “cool-down” interval the out-
put returns to the same condition as upon
initial power up. Power is again applied to
pin 2, the active LED will light, and monitor-
ing won’t begin for another three seconds.
A full short-circuit condition applied to the
Model 45DR’s party-line circuit will result
in a continuous cycle of four seconds on
(three seconds for start up and one second
for detection) and five seconds off.
External Party-Line Circuit
Operation
When the local power LED is not lit the
Model 45DR’s party-line interface is intend-
ed to be connected to an external party-line
circuit. The external circuit must provide
power and termination impedances to