Studio Technologies 47 - Manual (Page 22)

Issue 1, August 2010 Model 47 User Guide
Page 22 Studio Technologies, Inc.
47’s interfaces. If the nominal level is set
too low then sufficient audio headroom
might not be available. It can also result
in excessively high audio signals being
sent to 2-wire party-line circuits. Setting
the nominal level for too high a value will
reduce the signal-to-noise performance.
And, as expected, it may also result in
audio signals being sent to the 2-wire
circuits at too low a level. Begin a review
by confirming that the two 4-wire level DIP
switches associated with each interface
are set as required.
If the Model 47’s 4-wire nominal levels
are set correctly but the meters still reflect
sub-optimal levels, the issue may be relat-
ed to incorrect settings on the equipment
connected to the 4-wire inputs and out-
puts. It’s possible that although a connect-
ed 4-wire device’s nominal level matches
the Model 47’s level setting, its actual
nominal level may be significantly differ-
ent. With a digital matrix intercom system
this problem could be due to an incorrect
configuration having been made to a spe-
cific channel or port. For example, the RTS
ADAM system has a published nominal
level of +8 dBu, but using its configura-
tion 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 nominal value. This
should, at least in theory, lead to the best
system performance, including correct
interfacing with the Model 47. But often
it’s impossible to “clean up” the levels of
an existing system. In this case it may be
necessary to revise the Model 47’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 inter-
faces. 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 in-
correctly configured 2-wire nominal audio
level. Confirm that the DIP switch associ-
ated with each interface is set to match the
nominal level of the connected devices.
RTS user devices have a nominal level of
–10 dBu; Clear-Com devices typically have
a –14 dBu nominal level.
It’s also possible that an error is pres-
ent on the 2-wire party-line circuit. Signal
levels associated with 2-wire party-line
circuits depend on a single termination
being present. This termination, typically
200 ohms, 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 circuit,
will cause a “double-termination” condi-
tion. 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 47’s two dual-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 47’s internal 2-wire power sources
have been designated for supporting the
connected user devices.