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.

Circuit diagramHow to build Loudspeaker Protection with Soft Start - circuit diagramPart list
  • R1=22Kohm
  • R2-3=390Kohm
  • R4=470Kohm
  • R5=1Mohm
  • R6-7-8-9-10-12=10Kohm
  • R11=820 ohm
  • C1-2-3=47uF 63V
  • C4-5=100uF 25V
  • Q1=BC560C
  • Q2-3-4=BC550C
  • Q5=BD139
  • D1-2-3=1N4148
  • D4=Green 5mm Led
  • D5=Red 5mm Led
  • IC1=TL071
  • RL1=Relay 12VDc Omron G2R2
  • J1=3pin connector with 2.54mm step
  • J2=2pin connector with 2.54mm step
  • J3=2pin connector with 3.96mm step

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