Unit for automatic activation of priority contact of mixers/ amplifiers, to be used to interface telephone exchange boards (PABX) provided with dedicated audio output. A micro/line level audio signal must be applied to the input to trigger the output. Housed in a coated metal box and provided with unbalanced audio input with XLR 3-pole connector, input level adjustment, release time adjustment, status LED and audio output with DIN 5-pin connector for connection to mixers/amplifiers models PRE6, PRE5, A120MD, A240MD and A100M from which it receives 24Vdc power. Supplied with a 1-meter long connection cable with 5-pole DIN connectors at both ends.