Because the Clearcom type intercom bus runs at a significantly lower level than the Sony bus, the signal to the camera operator's headset must be boosted and the signal from the camera operator's microphone must be attenuated. To do this a very small circuit board is added to the camera containing this circuitry.
The earphone level is boosted with an LM386 integrated circuit which has a fixed gain of 20 dB. A potentiometer is provided to allow the camera operator to adjust the earphone volume. The rest of the circuit is derived from the manufacturer's data sheet. The LM386 is powered from a camera internal power bus.
Another potentiometer is provided to attenuate the microphone level. This is an internal screwdriver adjust pot since it is adjusted once at installation and not changed by the camera operator. Also provided is a microphone mute switch.