Sunday, March 04, 2018

Speaker Protector 3 Transistors

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 transistor.
Speaker Protector Circuit 3 Transistor

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:
Speaker Protector PCB Layout
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.

Video Assembling

Electronic Circuit is a good site for hobbyist also who would like to try DIY because it shared good circuits. If you have a personalized circuit requirement you may feel free to request it through the comment box or contact me.


Led at connect with collector transistor is indicate the relay on, and the other led is indicate signal output from amplifier.

Led at connect with collector 2n5551 transistor represent protect indicator while the two other led represent signal indicator

No, the led connect with collector that indicate the relay ON.