The auto terminate disable function should be used only when absolutely necessary; it’s possible that a significant downside could be experienced. With auto terminate disabled it’s important that properly ter- minated 2-wire party line-intercom circuits be connected to pins 2 or 3 on the Model 46’s 2-wire PL connectors. If they are not connected, it’s likely that audio oscilla- tions, noise, and distortion will be gener- ated in the Model 46’s 2-wire-to-4-wire converter circuitry. These audio artifacts will not cause any damage, but will be sent out the 4-wire line output connectors. Users of the 4-wire equipment may be less than pleased with what they hear!
Auto Null Button Operation
One pushbutton switch is associated with each of the Model 46’s two interface circuits. An advanced configuration pa- rameter allows selection of the button’s operation. The choices are dual auto null mode and independent auto null mode. When dual auto null mode is selected a single “tap” (press and release) of one of the two front-panel pushbutton switches initiates a routine that begins with chan- nel 1’s auto null sequence taking place followed immediately by channel 2’s auto null sequence being performed. Note that the mode selected for auto null button op- eration will also apply to the remote auto null inputs.
The independent auto null mode allows the auto null function to be initiated for each channel as desired. A single “tap” will start the auto null routine for channel
1.Two “taps” will start the routine for channel 2.
When DIP switch 2 is in its off (down) posi- tion the dual auto null mode is selected.
This is provided specifically for cases where the Model 46’s 2-wire party line interfaces will be used with dual channel intercom user devices. As an example: the RTS TW-series provides two independent audio channels, as well as power, over a single 3-conductor cable. In a case such as this it’s useful for both of the hybrid circuits associated with an interface to be auto nulled at approximately the same time. The dual auto null mode allows a single “tap” of the button to initiate nulling of both hybrid circuits.
When DIP switch 2 is in its on (up) posi- tion the independent auto null mode is selected. This would be appropriate for applications in which the two audio paths associated with each interface are used with independent party-line intercom circuits. This situation might arise when two Clear-Com single-channel intercom circuits are connected to one of the Model 46’s dual-channel interfaces. The hybrid circuit associated with each channel can be auto nulled as desired. Another exam- ple would be in an RTS TW-series applica- tion that uses source assignment panels. The “SAP” panels would be used to route multiple intercom channels to various sets of user devices as desired. In this case, the two channels associated with each Model 46 interface will often end up not routed to the same user device; indepen- dent auto nulling is certainly desired.
Refresh Disable
While testing the Model 46 as part of the development process it was found that in cases of extreme ESD (electro-static- discharge or “static”) an integrated circuit in the audio signal path could “latch up.” This would result in the audio signal no
