Power supply unit with dual note generator for intercom systems for 4+n system

Power supply unit for 4+n audio systems with both traditional and electronic call function. The power supply unit handles 2 inputs or one input and intercom service in automatic switching. It is equipped with protection in case of short circuit, 2 differentiated and enhanced call generators to call 4 electronic door phones in parallel without adding any additional device and 3 switches to allow switching between services and ensure conversation privacy.