unbalanced source in this manner results in hum or noise, connect XLR pin 2 to high (+ or hot) and pin 3 to shield; leave pin 1 unterminated.
4-Wire Line Outputs
The Model 45’s dual-channel interface pro- vides two analog line-level audio outputs. These outputs are intended to be connect- ed to inputs on the devices associated with the 4-wire audio signals. The outputs are capacitor coupled, transformer balanced with a nominal level of +4 dBu. The 4-wire line outputs are capable of driving inputs that have impedances as low as 600 ohms, however connecting to loads of 2 k ohms or greater is preferred. The line outputs are connected by way of 3-pin male XLR-type connectors which are located on the Model 45’s back panel. Refer to Figure 4 for a detailed view.
The mating connectors (females) should be prepared so that signal high (+ or hot) is expected on XLR pin 2. Signal low (– or cold) should be expected on XLR pin 3. The cables’ shields can be connected to XLR pin 1. However, in order to minimize the chance that ground-interaction prob- lems will arise, pin 1 on each of the line output connectors is isolated from all Mod- el 45 circuitry and ground points. “Floating” pin 1 virtually eliminates the chance that a “ground loop” problem will occur.
2-Wire Party-Line Intercom Connections
The Model 45’s 2-wire party-line intercom interface is designed to connect with a standard single- and dual-channel party- line intercom circuit. This type of circuit typically has positive 28 to 32 volts DC on pin 2 and common on pin 1. The Model
45’s 2-wire party-line interface can also serve as an intercom power source and 200 ohm impedance generator, allowing intercom user devices to be directly con- nected. The Model 45’s internal 30 volt DC intercom power source is limited to 300 milliamperes of current. This moder- ate amount of power requires that the type and number of connected user devices be selected appropriately.
For convenience, the 2-wire party-line intercom circuit or user devices can be connected to the Model 45 by way of either a male or female 3-pin XLR-type connector, both of which are located on the back panel. Refer to Figure 4 for a detailed view. The two connectors are wired in parallel (“multed”) and provide access to the identical signals.
Dual-Channel Intercom Systems
If compatibility with RTS TW-series is desired the mating connector (one male or one female) should be wired so that common is on pin 1, DC with channel 1 audio is on pin 2, and channel 2 audio is on pin 3. This wiring scheme applies whether the connected devices are to be powered by an external source or by the Model 45’s internal 2-wire intercom power source.
Single-Channel Intercom Systems
There are two ways of connecting to the Model 45’s 2-wire (PL) intercom connec- tors when compatibility with Clear-Com single-channel intercom devices is de- sired. The most direct method is to pre- pare a male or female 3-pin XLR mating connector so that common is on pin 1, power is on pin 2, and audio is connected on pin 3. With this connection scenario only audio channel 2, associated with
