Studio Technologies 45DC - Manual (Page 16)

Issue 1, January 2015 Model 45DC User Guide
Page 16 Studio Technologies, Inc.
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-compatible)
port such that it results in a nominal level of
–20 dBFS on the associated Dante chan-
nels. This should lead to the best perfor-
mance of the Model 45DC and associated
party-line user devices.
Audio Levels and Party-Line Termination
The FROM meters display the level of sig-
nals that come from the party-line circuit.
These signals are then sent as digital 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 (resistance 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 termination. This termina-
tion, 200 ohms nominally, is almost always
made at the power supply source. But it’s
possible that another 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. Remov-
ing the unwanted termination is the only
valid means of correcting the problem.
In most cases this will be simple to solve.
It’s easily possible for the Model 45DC’s
local power source, which also provides
200 ohm termination networks for the
audio channel, to be enabled when the
Model 45DC is connected to an externally-
powered party-line circuit. This would
be incorrect, leading to the “double-
termination” condition. Turning off the
Model 45DC’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 45DC’s operating power.
Party-Line Operating Mode
Selection
As discussed previously in this guide, the
Model 45DC provides two main operating
modes. One mode is used when a Model
45DC channel is required to create a par-
ty-line circuit, providing 28 volts DC and
a 200 ohm termination impedance. 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 45DC to be connected to an exist-
ing powered party-line intercom circuit. In
this mode the local power status LED will
not be lit. To select the desired operating
mode is simple, only requiring the audio