Studio Technologies 5130 2013 - Manual (Page 16)

Issue 5, July 2013 Model 5130 User Guide
Page 16 Studio Technologies, Inc.
Model 5130
Party-Line Interface Module
Operating Modes
To allow optimal performance in a variety
of applications the Model 5130 can func-
tion in either of two operating modes.
The difference between the two modes
is somewhat subtle, relating to how the
4-wire audio output muting function re-
sponds to the party-line interface’s DC
output current detection function.
When the Model 5130 has been config-
ured for operating mode 1 the two 4-wire
audio outputs will remain muted unless a
DC current of 15 milliamperes or greater
is actively being supplied by the 2-wire
party-line interface. This 15 milliampere
threshold was selected as being represen-
tative of what the smallest amount of DC
current a typical party-line device would
require. Requiring that a party-line device
be connected (as evidenced by DC cur-
rent being drawn) will minimize the chance
that undesirable audio signals will be sent
to the connected 4-wire equipment. These
undesirable signals would typically consist
of a portion of the 4-wire audio input being
“bounced” back through the Model 5130’s
unterminated 2-wire to 4-wire hybrid circuit.
This condition is especially undesirable
for optimal audio performance with 4-wire
intercom systems.
It might be helpful to clarify why operat-
ing mode 1 can be valuable. When the DC
current drawn from the party-line interface
is less than 15 milliamperes the module
determines that no party-line device, such
as a user beltpack, has been connected.
When no user device is connected it’s
probable that the Model 5130’s two 2-wire
to 4-wire hybrid circuits are not fully nulled.
If the circuits are not fully nulled then the
return loss value will be low and a large
percentage of the signal present on the
4-wire audio input will be “returned.” The
automatic muting of the 4-wire audio out-
puts will prevent this signal from being sent
to connected devices.
When the Model 5130 has been selected
for operating mode 2 the two 4-wire au-
dio outputs are always active. In operat-
ing mode 2 there is no requirement that a
minimum amount of DC current be drawn
from the 2-wire party-line interface. This
mode is provided for atypical but legitimate
applications where devices connected to
the Model 5130’s 2-wire party-line inter-
face do not draw DC current. (Or draw an
amount that’s less than the 15 milliam-
peres threshold.) Such devices might be
powered locally but are still intended to be
connected to party-line interface circuits
that have a –10 dBu (nominal) audio
operating level and a 200 ohm (nominal)
terminating impedance on each channel.
An example of this would be connecting
one of the Studio Technologies’ Model
200-Series of announcer’s or producer’s
consoles which is being locally powered.
(The Model 200-Series device can be pow-
ered by the Model 5130 but in most cases
an external source of 24 volts DC will be
connected.) In this case the Model 200-
Series device would be a completely “valid”
connection to the Model 5130 but no DC
current would be drawn by it. Only by
selecting operating mode 2 would it func-
tion correctly with the Model 5130.
Viewing and Changing the Operating
Mode
A Model 5130’s operating mode can be
viewed and, if desired, changed by way
of a power-up/button-press sequence.
With the Model 5130 in the un-powered
state (no source of 12 volt DC applied),
press and hold the auto null button. Then