This project is inspired by the article of the ELEKTOR magazine of july/august 1991. It is based on the basic principle of a loudspeaker delayed turn-on and DC entry detection (+ 1,5 V and - 0,7 V). This module lies between the amplifier output and the loudspeaker output. When the amplifier is powered on, a temporization of engagement of +/- 2,5 seconds delays the starting of the loudspeaker (avoiding power on thumps). If a continuous tension appears on the amplifier output this module immediately interrupts the loudspeaker line.
Leds indicate the working of the module (green = OK, red = temporization and/or DC detection). This project must be supplied with a small symmetrical independent PSU of + 12 V and - 12 V. When the amplifier is powered off, the loudpspeaker line is immediately interrupted. It is possible to place two relays in parallel on the circuit board to reduce the contact resistance and/or permit an important load commutation (from 10 to 20 amperes in the case of a strong power amplifier).
