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Issue 2, September 2007 Model 46 User Guide
Page 18 Studio Technologies, Inc.
Advanced
Configuration
Four DIP switches are provided on the
Model 46’s back panel. They allow the two
interfaces to be configured for several ad-
vanced operating modes. Refer to Figure
7 for a detailed view of these DIP switches.
The available modes include auto termi-
nate disable, auto null button operation,
refresh disable, and factory test.
are connected to the Model 46. In this lat-
ter case only one of the Model 46’s audio
channels will be used.
There may be situations where it’s nec-
essary for the two channels associated
with each Model 46 interface be used
with separate 2-wire party-line circuits.
An example of this might be where two
“loops” of single-channel belt packs,
such as units from Clear-Com, need to be
connected. Adapter cables as shown in
Figure 2 would be used. In this case the
intercom circuit’s DC power will not be
connected to the Model 46, but only to the
user devices. In this scenario, a DC volt-
age won’t be present on pin 2 or pin 3.
Another example of this might be where
adapter boxes with DC blocking are used
to interconnect intercom circuits with the
Model 46. In both these cases a DC volt-
age won’t be present on either pin 2 or 3
and the Model 46 will automatically apply
200 ohm terminations. In both these cases
the termination will be in error and will re-
sult in incorrect audio levels due a double-
termination condition.
To prevent this problem the auto termi-
nate function can be disabled. When DIP
switch 1 is in its off (down) position the
auto terminate function is active. When
switch 1 is in its on (up) position the auto
terminate function associated with each
interface is disabled. Repeating for clarity,
the auto terminate disable function applies
to both interfaces 1 and 2. With the auto
terminate function disabled the two 46
interfaces, when set for external power,
will operate normally with the exception
that pins 2 and 3 will never be terminated
by the Model 46’s circuitry.
Figure 7. Detail of back panel showing the
Advanced Mode DIP switches
Auto Terminate Disable
The auto terminate function is designed to
ensure that each 2-wire-to-4-wire interface
circuit remains stable under most oper-
ating conditions. Specifically, 200 ohm
impedances are automatically applied to
both pins 2 and 3 of a Model 46 2-wire
party-line interface when that interface is
configured for external power and no ex-
ternal source of intercom power is detect-
ed on pins 2 or 3. This function is directly
compatible with RTS TW-series intercom
applications in which the three conductors
of a cable support both DC power and two
channels of audio. It’s also compatible in
situations where all three conductors of a
Clear-Com single-channel intercom circuit