Speaker protection scheme
The Internet now presents a huge number of different sound amplifiers, for every taste and color, for any needed. As you know, even the most reliable amplifiers tend to fail, for example, due to improper operating conditions, overheating or improper connection. In this case, there is a high probability that the high supply voltage will be at the output of the amplifier, and, therefore, it will be unhindered right on the speakers of the speaker system. Thus, a failed amplifier diminishes behind itself “into the other world” the acoustic system connected to it, which can cost much more than the amplifier itself. That's why it's highly recommended to connect the amplifier to the speakers via a special board called the protection of speakers.One of the variants of such protection is shown in the diagram above.The protection works as follows: the signal from the amplifier output is fed to the IN input, and the speakers are connected to the OUT output. The minus of the amplifier is connected to the minus of the protection circuit and goes directly to the speakers. In the normal state, when the amplifier is working and the protection board receives power supply, the Rel 1 relay closes the board's input to the output and the signal goes directly from the amplifier to the speakers. But as soon as a constant voltage of at least 2-3 volts appears at the input, the protection is triggered, the relay turns off, thereby disconnecting the amplifier from the speakers. The circuit is not critical to the values of resistors and allows scatter. The transistor T1 can be set 2N5551, 2N5833, BC547, KT3102 or any other low-power npn transistor. T2 must be composite with a large gain, for example, BDX53 or KT829G. The LED on the circuit serves to indicate the status of the relay. When it is lit the relay is on, the signal goes directly from the amplifier to the speakers. In addition to protection against DC voltage, the circuit provides a delay in connecting the speaker system. After the supply voltage is applied, the relay does not turn on immediately, but after 2-3 seconds, this is necessary in order to avoid clicks in the speakers when the amplifier is turned on. The supply voltage of the circuit is 12 volts.The relay can be used any with a supply voltage of winding 12 volts and a maximum current through the contacts of at least 10 amperes. The button with the fixation S1 is displayed on the wires, it is needed to forcibly disable the relay, just in case. If this is not required, you can simply close the tracks on the PCB.
Device assemblyAmplifiers are most often designed for two channels, left and right, so the protection circuit must be repeated twice for each channel. For convenience, the board is divorced so that it already provides for the assembly of two identical circuits at once. The printed circuit board is manufactured by the LUT method, its dimensions are 100 x 35 mm.
Protection TestsNow that the board is completely ready, you can start testing. We supply power to the circuit (12 volts), two seconds later the relays must simultaneously click and the LEDs turn on. Now we take some source of constant voltage, for example, a battery, and connect it between the minus circuit and the input. The relay should immediately turn off. Remove the battery - the relay turns on again. You can connect a battery by changing its polarity, the circuit operates regardless of which polarity voltage appears at its input. We perform the same manipulations with the second circuit located on the same board. The protection threshold is approximately 2 volts. Now that the protection board has been tested, you can connect it to the amplifier and not be afraid that the speakers in expensive speakers will deteriorate due to the breakdown of the amplifier.Successful assembly.
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