Studio Technologies 46A - Manual (Page 21)

Model 46A User Guide Issue 1, September 2014
Studio Technologies, Inc. Page 21
If the Model 46A’s 4-wire nominal levels are
set correctly but the meters still reflect sub-
optimal levels, the issue may be related to
incorrect settings on the equipment con-
nected to the 4-wire inputs and outputs. It’s
possible that although a connected 4-wire
device’s nominal level matches the Model
46A’s level setting, its actual nominal level
may be significantly different. With a digital
matrix intercom system this problem could
be due to an incorrect configuration having
been made to a specific channel or port.
For example, the RTS ADAM system has
a published nominal level of +8 dBu, but
using its configuration software it’s possible
to set panels or ports to a level different
than nominal. The best solution in this case
is to adjust the intercom system so that its
levels comply with its own published nomi-
nal. This should, at least in theory, lead to
the best system performance, including
correct interfacing with the Model 46A. But
often it’s impossible to “clean up” the levels
of a existing system. In this case it may be
necessary to revise the Model 46A’s 4-wire
nominal level settings to match the reality
of the connected signals.
The TO 4-wire meters display the level of
signals that come from the 2-wire party-line
circuits and go out the 4-wire interfaces. An
issue may arise if the signals coming from
the connected party-line user devices aren’t
at a sufficient level so that a normal meter
display can be reached. This could be the
result of an incorrectly configured 2-wire
nominal audio level. Confirm that the DIP
switch, associated with each interface, is
set to match the nominal level of the con-
nected devices. RTS user devices have a
nominal level of –10 dBu; Clear-Com devic-
es typically have a –14 dBu nominal level.
It’s also possible that an error is present on
the 2-wire party-line circuit. Signal levels
associated with 2-wire party-line circuits
depend on a single termination being pres-
ent. This termination, typically 200 ohms,
is almost always made at the power sup-
ply source. But it’s possible that another
device, such as a second active power
supply on the same circuit, will cause a
“double-termination” condition. This leads
to a nominal 100 ohm line impedance
which will result in a level drop of at least
6 dB. Removing the unwanted termination
is really the only valid means of correcting
the problem.
Connecting Party-Line Devices
The Model 46A’s two 2-channel interface
circuits allow two sets of user devices to
be connected. Depending on the setting
of the configuration DIP switches, either
an external intercom power source or the
Model 46A’s internal 2-wire power source
has been designated for supporting the
connected user devices.
External Power Source
When set for an external 2-wire power
source, the Model 46A will not provide
power on pin 2 of the 2-wire connectors,
nor will the Model 46A use any power from
a connected intercom circuit. As expected,
audio signals will be sent from, and re-
ceived by, each interface’s two audio cir-
cuits. In this mode of operation the Model
46A acts as a typical user station on the
connected intercom circuit.
As a connection confirmation, hardware
and software in the Model 46A monitors
pins 2 and 3 of the 2-wire PL intercom
connectors for the presence of DC voltage.
A level greater than approximately 18 volts