This speaker protector circuit serves to protect the loudspeaker from the DC voltage that flows from the power amplifier, especially from the type of OCL power amplifier. In fact, the working system of the protector speaker circuit is simply delaying the connection between the amplifier and loudspeaker output for a few seconds. When the power amplifier is first turned on, there is usually a momentary voltage surge at its output. The problem is this surge voltage is a DC voltage which is, of course, dangerous when it flows on the loudspeaker. Below the circuit diagram of speaker protector, it's using 3 transistors.
82R x 1, 1K x 1, 8K2 x 2, 10K x 1, 47K x 2, 68K x 1, 180K x 1
100uF/35V x 4
1N4148 x 2, 1N4001 x 7, LED x 3
Relay 8 Pin DPDT
Transistor & IC
7812 x 1, 2N5551 x 3
PCB Layout Design:
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The workings of this protector speaker circuit is as a delay or also timer for the speakers that will connect to the amplifier when pwoer amplifier is turned on, as I have explained above. and the above circuit is used for stereo channel which only use 3 transistor as timer controller, and also not less important is the capacitor. If you want to change the working speed of the timer in the circuit you can replace the capacitor 100uF/35V near the 68K resistor, besides you also change the resistor itself. If the capacitor value gets bigger and the resistor gets smaller, the timer will longer work for the relay, and vice versa.