You should use a speaker protection circuit. To keep your speaker expensive! Sometimes your power amplifier may kill your speaker by accident.
This circuit is simple, small and inexpensive. The main parts are the transistor and relay to cut off the power. You can make it in a short time with pcb layout.
Why use the speaker protection circuit
In now a power amplifier usually build with a direct coupling circuit. The output of the power amplifier connects to the speakers directly.
This types of power amplifiers are good frequency response, high power, and cheap.
But they have an important disadvantage. If they damage.
With this voltage, make a coil of the speaker burns and lack eventually.
So if you do not want to the speaker—most expensive in the audio system—damaged.
You need to cut off this voltage not go out to a speaker with this circuit.
As shown below.
How it Works
How does the speaker protection circuit can prevent the speakers? As shown in this circuit has a lot of parts for a beginner. But you are not worried. I believe you can do it.
DC voltage protection
First of all, both resistors R1 and R2 reduce a lower some signal from the speaker. Then, after the capacitor, C1 serves to bypass this signal to ground.
However, if the power amplifier works error. There is the DC voltage to either positive or negative comes in.
Then, this voltage flows through the bridge diode circuit(D1 through D4) immediately. They rectifier only positive voltage to bias a base of Q1.
Now, Q1 works.
It makes the collector voltage low down. Next, the bias voltage at the base of Q2 will also lower down.
After that, both Q2 and Q3 stops run.
Thus, no current to relay RY1 and it cuts off the signal of a power amplifier from the speaker right away. The speakers are safe from DC power.
When you start the OCL power amplifier circuit. If no time on delay, we will hear noise sound “tup..” at the speaker briefly. It is a DC voltage swing. The speaker does not like it.
In this circuit help this problem.—Surge protection
While beginning power amplifier the relay does not work. So no sound on the speaker.
The first current comes to base Q2 slowly through R3. It does not turn on right away. Since the current charges to C2 until full. Then Q2, Q3, and relay work normally.
Also, Diode D6 protects Q2, Q3 from the high voltage pulse. That is generated in the relay coil when the relay is switched OFF.
Power supply source
You can choose one of the power sources between these 2 options.
- 9V AC—from the AC voltage source, secondary transformer.
- DC +12V—voltage from any source
It may better way you look at circuit below.
You may have two options.
- With transformer—since the speaker protection requires less than 0.2A. We should use one more transformer,0.3A. Here is how easiest.It is normal unregulated 12V supply.
- Without transformer—But if you have limited space. You cannot use a transformer. You may use some voltage of amplifier power supply. Which it has voltage 24V to 65V.We need to reduce voltage down to 12V 0.3A. The transistor and Zener diode regulator is good for this.
- You should use the TIP41C only. Because it can use with high voltage up to 100V
- If Vin is lower than 40V. Not use Rt limited current resistor. But Vin is upper than 40V. You should use Rt to limited current to a safe value.
How to use
- Connect the ground wire from the amplifier to ground of the protection speaker.
- Then, connect the signal output from the amplifier to the speakers. We connected it to the IN of the protection speaker to both the left and right.
- Next, connect the OUT signal from the speaker to the positive terminal of the protection speaker.
Testing this circuit on Multisim 13.0
Building and test circuit
- To produce the correct devices in the PCB. as Figure 2
- Check the soldering is done at every point.
- Test the functionality of the circuit. By connected power supply circuit. And see the LED to stick and hear a click with the relay working.
- Experiments, connected DC voltage at the IN of the anti-speakers, the LED will extinguish along with the relay will stop immediately.
If you do not follow this. Show that a failure occurs. Make sure to found before it is available.
If this circuit is too many hard. You do not need to use it.
Sometimes you may like circuit below.
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