Operation, Wire Mute during Auto Null

the Model 45’s 2-wire-to-4-wire converter circuitry. These audio artifacts will not cause any damage but will be sent out of the 4-wire line outputs. Users of the 4-wire equipment may be less than pleased with what they hear!

4-Wire Mute during Auto Null

As part of the auto nulling process audio tones are generated and sent out the

2-wire intercom interfaces. These tones, depending on the nulled state of the hybrid circuits, will also appear on the outputs of the 4-wire interface circuits. To prevent these unwanted tones from being sent to the inputs of the connected 4-wire devices by default the 4-wire outputs mute when the auto nulling process is active.

There may be cases, primarily at the fac- tory, where it’s desirable to have the null- ing tones appear on the 4-wire outputs.

Configuration DIP switch 5 allows the mut- ing of the 4-wire outputs to be disabled.

When switch 5 is in its off (down) posi- tion the Model 45 operates in its standard fashion. When switch 5 is in its on (up) position the 4-wire outputs will not mute during the auto nulling process. As ex- pected, when the Model 45 is deployed in the field switch 5 should remain in its off (down) position. However, no damage to the Model 45 or connected equipment will occur when muting during auto null is disabled.

Operation

Upon power-up the Model 45 will always go through a short initialization sequence before normal operation will begin. The LEDs will light sequentially and, upon

completion, the applicable input power LED will light. The null settings for the two hybrid circuits are recalled and used, hav- ing been previously stored in nonvolatile memory.

Significant user intervention is typically not required during normal Model 45 opera- tion. The unit is designed for continuous operation with no routine adjustment or maintenance necessary. Assuming that the desired configuration has been select- ed using the DIP switches, only occasion- ally activating the auto null function should be necessary. The latter may be warranted should connected user devices or wiring associated with the 2-wire party-line inter- com circuit be changed.

External 24 Volt DC Power Source

In many applications an external source of 24 volts DC will be connected to the Model 45. Typically this will be in the form of the external power supply provided with the unit by Studio Technologies. The 24VDC input power status LED will light whenever the external source is providing power for the unit’s circuitry. In this sce- nario the Model 45 can be configured as to whether or not it acts as a power source for the 2-wire party-line interface circuit.

When the Model 45 is not Serving as the 2-Wire Intercom Power Source

When an external source of 24 volts DC is connected and the Model 45 is configured to not provide 2-wire party-line intercom power (configuration DIP switch 2 set to off), the unit will not provide power to, nor take power from, pin 2 of the 2-wire (PL) connectors. The 4-wire inputs and out- puts, as well as the internal power supply,

Model 45 User Guide	Issue Preliminary 2, March 2009
Studio Technologies, Inc.	Page 19