Studio Technologies 5132 2012 - Manual (Page 11)

Model 5132 User Guide Issue 4, September 2012
Studio Technologies, Inc. Page 11
Model 5132
Party-Line Interface Module
two intercom channels. (Technically, in-
dependent nominal 200 ohm AC-coupled
loads are connected from pin 2 to pin 1
and from pin 3 to pin 1.) If user beltpack
devices are going to be directly connected
and powered by the Model 5132 the
internal party-line power function must
be enabled.
If the Model 5132’s party-line intercom
interface is going to be connected to an
existing party-line intercom system the
Model 5132’s party-line power source
should be turned off. In this mode the LED
labeled PL POWER (+28V) will not be lit,
+28 volt DC will not be applied to pin 2,
and 200 ohm audio terminations will not
be provided.
If the Model 5132’s internal party-line
power source is enabled when the inter-
face is connected to an existing party-line
intercom system no damage will result. But
the audio levels will no longer be correct as
the intercom channels will now be “double
terminated.” The Model 5132’s 200 ohm
terminations will be active at the same time
as those of the external intercom circuit.
The intercom “bus” termination will drop
to approximately 100 ohms and the audio
level will drop by at least 6 dB. This will
cause audio level issues for users as well
as preventing satisfactory Model 5132 auto
nulling from being able to take place.
Auto Null
The Model 5132 contains circuitry to
automatically null the two 2-wire-to-4-wire
interfaces. Normally this process is per-
formed at the time of initial Model 5132
user set up and operation, but there’s no
reason why “auto nulling” can’t be initiated
anytime one desires. The only time that
auto null must be performed is if conditions
have changed vis-à-vis the party-line inter-
com user devices, the wiring connected to
a Model 5132’s party-line intercom inter-
face connector, and, if present, an external
party-line intercom circuit. Even a slight
change to a party-line intercom circuit,
such as adding or removing a section of
cable, is sufficient to require that the auto
null process be performed.
A pushbutton switch, located on the Model
5132’s front panel, is used to activate the
auto null process. To initiate auto null re-
quires simply pressing and releasing (“tap-
ping”) the button. An LED provides a visual
indication of the auto null process, flashing
when the auto null process is active. The
sequence takes less than 15 seconds to
complete.
An auto null sequence begins with the
muting of the 4-wire audio input and output
signal paths. This is followed by a short
period of 24 kHz signal that is sent out
both the party-line intercom interface
channels. This will turn off microphones
on those connected user devices that are
compatible with the RTS TW-series “mic
kill” protocol. The actual auto nulling pro-
cess is performed next. A series of tones
will be sent out the party-line interface
channels. Other Model 5132 circuitry,
under software control, will rapidly perform
adjustments to achieve the best null pos-
sible. After the null adjustments have been
made the results are stored in nonvolatile
memory. Once the process is complete
the audio input and output paths are again
activated.
If possible, prior to performing an auto
null it’s polite to warn all personnel who
are actively using the connected party-line
intercom devices. The tones sent to the
party-line intercom channels during the