Manual

Issue 3, March 2016 Model 45DC User Guide
Page 18 Studio Technologies, Inc.
mode is simple, only requiring the audio
null pushbutton switch of the desired in-
terface channel 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 for each
interface channel will be stored in nonvola-
tile 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
create a single-channel party-line circuit.
The party-line interface supplies 28 volts
DC on pin 2 of the 3-pin XLR connectors.
A maximum current draw of 150 mA per
interface is available. This current is suffi-
cient to power 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 fig-
ure to calculate but a web search will gen-
erally 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 cur-
rent 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 mini-
mal 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
firmware, indicating that normal operation
is taking place. This helps to prevent un-
wanted audio signals from passing to 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 protection
of the Model 45DC’s circuitry. Upon initial
Model 45DC party-line intercom power up
no monitoring of the intercom power out-
puts takes place for three seconds. This
allows the Model 45DC’s circuitry and the
connected intercom user devices to sta-
bilize. The active LEDs, which monitor the
DC voltage on pin 2 of the 3-pin XLR con-
nectors associated with the intercom chan-
nels, will light to indicate that an output is
active. After this initial delay period moni-
toring 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 firmware 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 continuous cycle of four seconds
on (three seconds for start up and one
second for detection) and five seconds
off on that specific circuit.