ADAM system has a published nominal level of +8 dBu, but using its configuration software it’s possible to set panels or ports to a level different than nominal. The best solution in this case is to adjust the inter- com system so that its levels comply with its own published nominal. This should, at least in theory, lead to the best system performance, including correct interfacing with the Model 46. But often it’s impos- sible to “clean up” the levels of a existing system. In this case it may be necessary to revise the Model 46’s 4-wire nominal level settings to match the reality of the connected signals.
The “to 4-wire” meters display the level of signals that come from the 2-wire party- line circuits and go out the 4-wire inter- faces. An issue may arise if the signals coming from the connected party-line user devices aren’t at a sufficient level so that a normal meter display can be reached. This could be the result of an incorrectly configured 2-wire nominal audio level. Confirm that the DIP switch, associated with each interface, is set to match the nominal level of the connected devices. RTS user devices have a nominal level of –10 dBu; Clear-Com devices typi- cally have a –14 dBu nominal level.
It’s also possible that an error is pres- ent on the 2-wire party-line circuit. Signal levels associated with 2-wire party-line circuits depend on a single termination being present. This termination, typically 200 ohms, is almost always made at the power supply source. But it’s possible that another device, such as a second active power supply on the same circuit, will cause a “double-termination” condi- tion. This leads to a nominal 100 ohm line impedance which will result in a level drop
of at least 6 dB. Removing the unwanted termination is really the only valid means of correcting the problem.
Connecting Party-Line
Devices
The Model 46’s two dual-channel interface circuits allow two sets of user devices to be connected. Depending on the setting of the configuration DIP switches, either an external intercom power source or the Model 46’s internal 2-wire power source has been designated for supporting the connected user devices.
External Power Source
When set for an external 2-wire power source, the Model 46 will not provide power on pin 2 of the 2-wire connectors, nor will the Model 46 use any power from a connected intercom circuit. As expected, audio signals will be sent from, and re- ceived by, each interface’s two audio cir- cuits. In this mode of operation the Model 46 acts as a typical user station on the connected intercom circuit.
As a connection confirmation, hardware and software in the Model 46 monitors pins 2 and 3 of the 2-wire PL intercom connectors for the presence of DC volt- age. A level greater than approximately 18 volts DC on pin 2 will cause the status LED labeled pin 2 to light. A level greater than 18 volts DC on pin 3 will cause the pin 3 status LED to light.
The author is aware that user intercom devices almost always draw power from pin 2 rather than pin 3. However, in many broadcast applications, power is provided on all intercom paths so that flexible chan- nel assignments can be made. In the
