are often part of broadcast and production audio applications. While the output cir- cuitry is not intended to be “on-air” quality, overall audio performance should be very good. Devices connected to the line-level talkback outputs can range from amplified loudspeakers, analog inputs on intercom systems, and input channels associated with audio consoles. Connecting the out- puts to devices that allow easy control of the signal level can be helpful. For exam- ple, connecting to spare input modules on an audio console provides the flexibility to add gain or attenuate as required. Dedi- cated talkback-associated outputs on the audio console can then be routed to the final destination(s).
As previously mentioned, the line-level talkback outputs on multiple Model 233 units can be directly connected together. Using a simple “Y” or “W” cable, this pas- sive summing (adding together or “bridg- ing”) of talkback signals allows one audio cable to serve as a master talkback path. A side effect from using this passive sum- ming technique is that signal attenuation will occur. The audio quality won’t suffer, but an audio “pad” is created. If two line- level talkback outputs are connected to- gether, a signal attenuation of 6 dB can be expected. Connecting three talkback out- puts together will result in 9.5 dB of atten- uation. And four talkback outputs “multed” together will lead to 12 dB of attenuation. In most cases this attenuation won’t pose a problem. Typically a device that receives the talkback signal, such as an amplified loudspeaker, will have an adjustable input sensitivity so this attenuation won’t prove to be a problem.
Line Inputs
The Model 233 allows two line-level audio sources to be connected. These sources
can be individually routed to the left chan- nel, right channel, or both the left and right channel of the headphone outputs. The inputs are balanced, transformer-coupled with a nominal impedance of 10 k ohms. Capacitors, in series with the transformer’s input leads, prevent a DC voltage present on a connected source from impacting performance. The line inputs are compat- ible with signals that have a nominal level of –12 dBV to +6 dBu. Two trim poten- tiometers, located on the bottom of the Model 233’s enclosure, allow signals over this wide nominal level range to be effec- tively utilized.
Audio sources are connected to the line inputs by way of 3-pin female XLR-type connectors which are located on the unit’s back panel. Prepare the mating connec- tors (males) so that pin 2 is signal high (+ or hot), pin 3 is low (– or cold), and pin 1 is shield. If connecting a source in this manner results in hum or noise, it’s pos- sible that removing the shield connection from pin 1 can eliminate the issue. With an unbalanced source connect pin 2 to signal high (+ or hot) and both pins 1 and 3 to shield. If connecting an unbalanced source in this manner results in hum or noise, connect pin 2 to high (+ or hot) and pin 3 to shield; leave pin 1 unterminated.
Intercom Interface
The Model 233’s intercom interface is designed to directly connect with standard single- and dual-channel party-line inter- com lines. The one or two audio signals provided by the intercom line can serve as audio sources for the headphone outputs. Each signal can be individually assigned to the left channel, the right channel,
or both the left and right channels. The Model 233 can also be configured to send talkback audio to either or both of the
