Loudspeaker Protection with Soft Start circuit and explanation

Loudspeaker Protection with Soft Start


This is a small protection circuit from loudspeakers, from DC voltage that likely to exist after some damage in the power amplifier. If a DC voltage is presented in the exit of amplifier, RL1 it interrupts immediately the line of loudspeakers preventing thus to reach in he. Parallel it provides a delay time of 3 seconds from the moment where the power supply will be applied. This delay protects the loudspeakers from undesirable bangs that are observed when open the supply switch. The Leds D 4-5 provide a optical indication for the circuit operation [D4 (green)=OK and D5(red)= delay or presence DC voltage]. The supply of circuit becomes from a symmetrical ?12Volts, which we can take from small independent power supply or from afterwards suitable demotion of main power supply. It will be supposed you make a circuit of protection for each final amplifier that you dispose. Proportional attention it should you show for the quality of RL1 that the contacts of will be supposed to bear the current that passes from he.

Part List
R1=22Kohm
R2-3=390Kohm
R4=470Kohm
R5=1Mohm
R6-7-8-9-10-12=10Kohm
R11=820 ohm
RL1=Relay 12VDc Omron G2R2
C4-5=100uF 25V
C1-2-3=47uF 63V

IC1=TL071
Q1=BC560C
Q2-3-4=BC550C
Q5=BD139
D1-2-3=1N4148
D4=Green 5mm Led
D5=Red 5mm Led

J1=3pin connector with 2.54mm step
J2=2pin connector with 2.54mm step
J3=2pin connector with 3.96mm step