Studio Technologies 45DC - Manual (Page 17)

Model 45DC User Guide Issue 1, January 2015
Studio Technologies, Inc. Page 17
null pushbutton switch of the desired inter-
face channel to be pressed and held for two
seconds. The mode will change and the lo-
cal power LED will display accordingly. The
button can then be released. The selected
operating mode for each interface channel
will be stored in non-volatile memory so that
they will restore after a power-down/power-
up cycle.
Local Power Mode Operation
When a channel’s local power LED is lit the
Model 45DC provides party-line power and
a 200 ohm termination impedances to cre-
ate a single-channel party-line circuit. The
party-line interface supplies 28 volts DC on
pin 2 of the 3-pin XLR connectors. A maxi-
mum current draw of 150 mA per interface
is available. This current is sufficient to pow-
er intercom user devices such as beltpacks.
A common entertainment or corporate
application might use Clear-Com RS-501
or RS-701 beltpacks. Select the connected
devices so that their total maximum current
doesn’t exceed 150 mA. That’s not always
the easiest figure to calculate but a web
search will generally find specifications for
all commonly used devices. For example, a
search finds that the ubiquitous RS-501 will
consume a maximum of 50 mA of current.
According to this figure up to three of these
units can be connected to a Model 45DC. A
newer version, the RS-701 has a quiescent
current draw of 12 mA and an approximate
maximum of 23 mA. From this information
one could estimate that up to five of these
units can easily be supported.
The active LED will light when a minimal
amount of current is flowing from the Model
45DC intercom interface to the connected
user device or devices. This current,
approximately 5 mA, provides a “circuit-
active” signal to the Model 45DC’s firm-
ware, indicating that normal operation
is taking place. This helps to prevent un-
wanted audio signals from passing to and
from the Dante audio channels when no
party-line devices are connected.
The Model 45DC’s two party-line intercom
power supply circuits operate indepen-
dently under firmware control. This allows
detection of fault conditions and protec-
tion of the Model 45DC’s circuitry. Upon
initial Model 45DC party-line intercom
power up no monitoring of the intercom
power outputs takes place for three sec-
onds. This allows the Model 45DC’s cir-
cuitry and the connected intercom user
devices to stabilize. The active LEDs,
which monitor the DC voltage on pin 2 of
the 3-pin XLR connectors associated with
the intercom channels, will light to indicate
that an 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 continuous
1-second interval. The hardware and firm-
ware responds to this condition by turning
off the associated power source to pin 2
and flashing the active 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 active LED will light,
and monitoring won’t begin for another
three seconds. A full short-circuit condition
applied to either of the Model 45DC’s
party-line circuits will result in a con-
tinuous cycle of four seconds on (three
seconds for start up and one second for
detection) and five seconds off on that
specific circuit.