A ‘four-wire’ communication unit for use ‘in a multitude of TV and radio broadcasting applications’, including talkback / cue, IFB and commentary, the CM-BH4W uses audio transformers at its input and output, providing galvanic isolation from outside interference, ensuring communications are ‘loud and clear, every time’. It has a 3-pole, 6.35mm jack socket for connecting a headset and female and male, 3-pin, XLR connectors for line-level input and output, respectively. There is a rotary, combined, on/off and volume control and a press-to-talk button. A switch on the side selects IFB or four-wire mode.

In four-wire mode, the unit acts as a two-way intercom, with input audio routed to the headset earpiece, and microphone audio is routed to the output upon pressing the talk button. The output level is maintained at +2dBu peak level by a built-in AGC. In IFB mode, the input audio is routed to the output, and is interrupted by the microphone signal when the talk switch is pressed. The talk switch can easily be converted from momentary to latching operation to suit your application.