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 diagram
Part 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
