Chairman unit provides 3.5mm unbalanced headphone mini jack and 3.5mm unbalanced record output mini jack with volume control, 32 ohms headphone and 10 kiloohms, –20dB recording. It uses TS-773 or TS-774 gooseneck microphone Controls of chairman unit shall include talk key which shall provide microphone and speaker on-off control. Controls of chairman unit shall also include priority key which provides microphone and speaker on-off control, other microphone off and single-tone chime activation. It provides contact closure output (24Vdc, maximum 50mA) when microphone is active. It also provides built-in speaker (130 ohms, 200mW). It shall be powered by TS-770 central unit supplying 35Vdc, under 30mA line. Case of chairman unit shall be constructed of ABS resin with black finishing. Panel of chairman unit shall be constructed of ABS resin with gray metallic paint and 50% glossy finishing.