Studio Technologies 45DR, User Manual

Page: 16 / 23

Issue 2, January 2015 Model 45DR User Guide
Page 16 Studio Technologies, Inc.
port. For example, the RTS ADAM system
has a published nominal level of +8 dBu,
but it’s not clear how this translates into a
digital audio level on an associated Dante
channel. Using its configuration software
it’s most likely possible to set the nominal
level of intercom key panels or ports to
something different than +8 dBu. The best
solution in this case would be to adjust
the associated OMNEO (Dante-compat-
ible) port such that it results in a nominal
level of –20 dBFS on the associated Dante
channels. This should lead to the best per-
formance of the Model 45DR and associ-
ated party-line user devices.
Audio Levels and Party-Line Termination
The FROM meters display the level of
signals that come from the party-line cir-
cuit. These signals are then sent as digi-
tal audio to the associated Dante output
channels. An issue may arise if the signals
coming from the connected party-line
circuit or user devices aren’t at a sufficient
level so that a normal meter display level
can be reached. For a party-line circuit to
function correctly the impedance (resis-
tance to AC signals such as audio) must
be approximately 200 ohms. Typically to
achieve this depends on a single piece of
equipment providing a single audio termi-
nation. This termination, 200 ohms nomi-
nally, is almost always made at the power
supply source. But it’s possible that anoth-
er device, such as a second active power
supply on the same party-line circuit, will
cause a “double-termination” condition.
This will result in a 100 ohm party-line
circuit impedance and an audio level drop
of about 6 dB. Removing the unwanted
termination is the only valid means of cor-
recting the problem.
In most cases this will be simple to solve.
It’s easily possible for the Model 45DR’s
local power source, which also provides
200 ohm termination networks for the two
channels, to be accidentally enabled when
the Model 45DR is connected to an exter-
nally-powered party-line circuit. This would
be incorrect, leading to the “double-termi-
nation” condition. Turning off the Model
45DR’s local power source by pressing
and holding the auto null button is all that
is required.
Power Status LEDs
Two green LEDs are located on the front
panel and are associated with operating
power. The PoE LED indicator will light
whenever an Ethernet connection with
Power-over-Ethernet (PoE) capability is
connected. The DC power LED will light
whenever an external DC voltage has
been applied. The acceptable range is 10
to 18 volts DC. If both power sources are
present the PoE source will provide the
Model 45DR’s operating power.
Party-Line Operating Mode
Selection
As discussed previously in this guide, the
Model 45DR provides two main operating
modes. One mode is used when the Mod-
el 45DR is required to create a party-line
circuit, providing 29 volts DC and 200 ohm
termination impedances. In this mode user
devices such as beltpacks can be directly
supported. When this mode is selected
the local power status LED will be lit. The
second mode allows the Model 45DR
to be connected to an existing powered
party-line intercom circuit. In this mode
the local power status LED will not be lit.
To select the desired operating mode is