Many electronics circuits and projects for learning in simple ways.

Speaker protection circuit

Is the speaker expensive? Sometimes your power amplifier may kill your speaker by accident. So, you need to use the speaker protection circuit.   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.  But it can maintain your speakers.

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.

An OCL amplifier pattern uses a Dual power supply. It has three wire power, positive, negative and ground.

This types of power amplifiers are good frequency response, high power, and cheap.

But they have an important disadvantage. If they damage.

Sometimes, their output may have a positive or negative higher voltage to immediately the speakers.

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.

The speaker protection circuit

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.

Soft start

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.

While beginning power amplifier the relay does not work. So not sound on the speaker. Why?

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 works normally.

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

How to use

  1. Connect the ground wire from the amplifier to ground of the protection speaker.
  2. 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.
  3. Next, connect the OUT signal from the speaker to the positive terminal of the protection speaker.


Building and test circuit.

  1. To produce the correct devices in the PCB. as Figure 2
  2. Check the soldering is done at every point.
  3. 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.
  4. 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.

PCB-of-the-speaker-protection
Figure 2 The PCB layout and components layout of this project

If this circuit is too many hard. You do not need to use it. Sometimes you may like circuit below.

Simple delay speakers

This circuit is small-sized circuit at can build easy, and usable get easy between a loudspeaker with an amplifier. By have relay be switch edit during opening-time switch that stereo will hear the sound “tlub” come out from the loudspeaker.

Simple delay speakers

Which this sound is sound the electricity will pull sharply to flow enter still a loudspeaker and may make a loudspeaker can are damaged therefore then necessary to must have time drag while open switch for a moment.

For speak, this part disappears before then build enter still a loudspeaker.

When receiving power supply come in, The C1 will charge thereafter C2 begin charge change R1. When C2 charge full until go to bias give Q1 work go to current driver give relay. Which use relay model double contract, make contract switch touch.

From that time build a loudspeaker suits power amplifier the period will delay to depend on the value C2. If want to give can delay long ago enhance the value C2. But if give can delay short down devalue C2.

This Post Has 12 Comments

  1. This website contents is very old. However is a very helpful to my students.
    Thank you.

  2. This circuit is very simple to make and very useful.
    Thank you for help us.

  3. very nice and simple circuit

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  5. so if we need the same circuit for 5.2 Audio System means , how we can modify the circuit , And y we r connecting the speakers in serious , output line of the speaker should be in parallel to each other …

  6. Sureshkanna: you missed the ground that’s between the speakers, i.e Parallel in the end.

    for 5.1 just add 5.2K resistor in series as currently, and add how much output you want.

    I run simulations on it seems to be working fine, will try practically, Going to use it for DIY 5.1 Amplifier.

  7. Hi. Will this circit work with amp which have +-56V at output transistors?

  8. Than you for the circuit. u tested this circuit perfectly working for dual DC components positive dc component and negative dc component. i want to add 5 sec delay to this circuit. Please suggest.

    1. Hi L Srinivasa Murthy A,
      Thank you too, for visiting. I am so happy your project works. You can adjust delay time with C2-100uF. You may try to increase capacitance up to 220uF take longer time. I hope it will work well.

  9. What does AC9V, DC12 mean on the first schematic?
    Would the above mean I can use either a 9VAC voltage or a 12VDC voltage.

    1. We use the power supply of this circuit in two ways of choosing.  
      9V AC—from the AC voltage source, secondary transformer. 
      DC +12V— voltage from any source 

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