User manual ASL INTERCOM PS 19

[. . . ] ASL has taken great care to ensure this product reaches you in flawless condition. 3. 0 INSTALLATION To connect the PS 19 onto the intercom system, use professional flexible microphone cable with 2 wires and 1 shield only. Connect the system intercom cable into the LINE connector socket on the rear panel. Finally connect the listening headset plug into the HEADSET connector, also on the rear panel. The PS 19 is fully protected against mis-wiring (reverse power) or short-circuit in the interconnecting cables. This PS 19 will form part of an existing or new intercom system, and connection to it is straightforward. [. . . ] The male connector is for extending the intercom line to other user stations. 7 HEADSET connector An XLR-4 type connector for the connection of the local headset. This must have a can impedance of 200 ohms (or greater), or each 400 ohms minimum when in parallel. phones - 6. 0 INTERNAL CONTROLS MIC GAIN The mic gain can be adjusted internally by a trimmer. To decrease mic gain turn counterclockwise. User Manual PS 19 / Issue 1 © 1994 ASL Intercom, Utrecht, Holland. 5 7. 0 CABLING For the PRO Series Intercom system the interconnecting cables are of the shielded two-conductor microphone cable type and the intercom line connectors are of the XLR-3 type. XLR pin 1 is connected to the shield of the cable which functions as the common return for audio and power. Since the audio signal is transferred in an unbalanced Ú way, certain rules have to be obeyed when installing the cables of an intercom network. This is to avoid earth loops and to minimize power loss and the possible effect of electromagnetic fields. For interconnecting user stations, power supplies and accessories in an ASL Intercom network, use high quality shielded two-conductor (minimum 2x 0. 30 mm2) microphone cable only. In case of a multi channel intercom network, use high quality microphone 'multipair' cable only, each pair consisting of two conductors (minimum 2x 0. 15 mm2) with separate shield. Use flexible single and multipair microphone cable instead of cable with solid cores, especially when the cable is subjected to bending during operation or installation. The screen of each separate microphone cable and/or the screen of each single pair in a multipair cable, should be connected to pin 1 of each XLR-3 connector. Do not connect this cable screen to the metal housing of the connector or to metal wall boxes (outlets). Cable trunks, connection boxes and overall multipair cable screen to clean earth. Metal cable trunks, metal connection boxes and overall multipair cable screen should be interconnected and, at one point (the 'central earthing point') in the intercom network only, be connected to a clean earth or a safety earth. Keep metal connection boxes and cable housings isolated from other metal parts. Metal housings for intercom cables and connectors should be mounted in such a way that they are isolated from other metal cable and connector housings and from any other metal construction parts. When two (multi channel) units in a network are connected by more than one cable, make sure that these cables are parallel to each other over the whole distance between those units. When using multipair cable, parallelism is ensured in the best possible way. [. . . ] One wire is used as an audio line, one as a power line and the screen of the cable functions as earth/return. Each station utilises a current amplifier to amplify the microphone signal and place it on the common audio line where, due to the constant line impedance (situated in the power supply between XLR pin 3 and 1), a signal voltage is developed which can be further amplified and sent to headphones or loudspeakers. This principle has three advantages: - the use of a single audio line allows several stations to talk and listen simultaneously. - due to the high bridging impedance offered by each station, the number of stations 'on line' has no influence on the level of the communications signal. [. . . ]