Main Output
The Model 233’s main output is intended to be the “on-air” or primary signal that typi- cally connects to the input of an audio con- sole. The output is transformer balanced with a nominal signal level of –2 dBu. The actual level will depend upon the gain set- ting of the microphone preamplifier, sen- sitivity of the microphone, and how loudly the user speaks into the microphone. The transformer used in the main output is in- tended for professional audio applications. Its source impedance is very low and can drive lengthy cable runs without difficulty. It is capable of driving loads as low as 600 ohms but performs best with loads of 2 k ohms or greater. (This should not prove to be an issue as virtually all contemporary audio equipment has a relatively high input impedance.) As the secondary winding of the output transformer connects directly to the main output connector, care should be taken so that a DC voltage is never present on the interconnecting cable.
The main output is interfaced by means of a 3-pin male XLR-type connector located on the Model 233’s back panel. The inter- connecting cable’s mating connector (female) should be wired so that signal high (+ or hot) is on pin 2 and signal low (– or cold) is on pin 3. The cable’s shield can be connected to pin 1, but it will have no function. Also, the cable’s shield must not be terminated on the metal “shell” con- nection of the mating connector. To limit the chance of grounding interaction be- tween the Model 233 and connected equip- ment, pin 1 on the main output’s connector is isolated from any point in the Model 233. The fact that pin 1 “floats” will minimize the chance of hums, noises, or buzzes being present on the equipment connected to the main output.
Line-Level Talkback Outputs
The two line-level talkback outputs are intended to be connected to control rooms, production trailers, or other loca- tions where talent-originated voice cues are required. The outputs are transformer balanced with a nominal level of +4 dBu. To enhance talkback audio quality, a com- pressor circuit controls the dynamic range of the signal coming from the microphone preamplifier.
For protection against accidental connec- tion to cables that have DC power present, the line-level talkback outputs are capaci- tor coupled. In series with the talkback output leads are 300 ohm resistors, mak- ing the effective output impedance ap- proximately 600 ohms. These resistors create a passive summing network, allow- ing talkback outputs on multiple Model 233 units to be connected (“bridged”) together.
The line-level talkback outputs are con- nected by way of two 3-pin male XLR- type connectors which are located on the Model 233’s back panel. The mating connectors (female) should be prepared so that signal high (+ or hot) is provided on pin 2. Signal low (– or cold) should be provided on pin 3. The cables’ shields can be connected to pin 1. But, like the main output, in order to minimize the chance that ground-interaction problems will arise, pin 1 on the line-level talkback output connectors are isolated from the Model 233’s chassis and circuitry. By making pin 1 “float,” often-feared “ground loop” problems shouldn’t arise. Note that the metal shell of the mating connector must also be “floating.”
The line-level talkback outputs are in- tended to drive the lengthy cable runs that
