AT 40T volume control is made of a control circuit having a selector and a separated transformer. It can be used in 100V line systems to adjust the volume level of a loudspeaker group having a total power not exceeding 40W. All connected loudspeakers shall have 100V line matching transformers. It includes a 24V dc override relay to either bypass the 6 position (5 + off) selector or insert a second 100 V line (not affected by the volume control) for paging. It can operate with 3 wire lines as well (in order to make emergency announcements without using the internal 24V dc relay). AT 40T can be installed on whichever supporting frame for home / office electrical systems by drilling a hole in a blank key and fixing the control circuit. 3 knobs are included in 3 different colours: white, silver, anthracite.