Studio Technologies 5132 2014 - Manual (Page 11)

Model 5132 User Guide Issue 5, October 2014
Studio Technologies, Inc. Page 11
Model 5132
Party-Line Interface Module
on and power off modes. When the LED
located next to the pushbutton is lit 28
volts DC will be applied to pin 2 of the XLR
connector. In addition, audio terminations
(200 ohm AC loads) will be connected to
the two intercom channels. (Technically,
independent 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 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 to be connected to an existing
party-line intercom circuit 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 circuit 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 auto-
matically null the two 2-wire-to-4-wire inter-
faces. Normally this process is performed
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 intercom user
devices, the wiring connected to a Model
5132’s party-line intercom interface con-
nector, and, if present, an external party-
line intercom circuit. Even a small change
to a party-line intercom circuit, such as
adding or removing a section of cable, can
be sufficient to require that the auto null
process be performed.
The Auto Null pushbutton switch, located
on the Model 5132’s front panel, is used
to activate the auto null process. To initi-
ate auto null requires simply pressing and
releasing (“tapping”) the button. An associ-
ated 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.
The auto null function can only be enabled
if the party-line interface is fully active. This
requires a party-line current draw of ap-
proximately 5 miiliamperes or more if the
Model 5132 is selected to provide party-
line power. If the module is selected to
interface with an external party-line circuit
a voltage of greater than approximately
18 must be present on pin 2 of the inter-
face connector. If either of these conditions
is not met the auto null function cannot
be enabled. This will be indicated by the
Auto Null LED flashing rapidly for a few
seconds.
An auto null sequence begins with the
muting of the line-level 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