Audio Amplifier | Simple & Powerful

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About: Creative Electrical Projects

This amplifier is simple but pretty powerful, it uses just one MOSFET transistor in it.

Step 1: Watch the Video!

Step 2: Get the Main Components for This Project

  1. MOSFET transistor IRF540N (you can use similar N-Channel MOSFET)
  2. 47K 0.25W or 0.125W (it is not critical, you can use a 10K - 100K resistor)
  3. 12 Volts 21 Watt light bulb. A light bulb works as a powerful resistor. It is difficult to find for example a 21W resistor, that is why I use a lightbulb instead. You can use 1W - 40W light bulb. The more powerful light bulb you use the more powerful amplifier you'll get. But for a powerful amplifier you will need a powerful power source as well, and a big heatsink.
  4. 4.7uF capacitor. (2.2uF to 10uF capacitors will work fine as well)
  5. 1000uF capacitor. (470uF to 2200uF capacitors will work fine as well.

Both capacitors should be 16V or higher!

Step 3: Get Additional Components

  1. Audio jack
  2. Heatsink
  3. Wires

Step 4: Assemble Components According to the Circuit

Step 5: Check the Wiring

Step 6: Connect a Power Source

The power source can be a 12V battery or a 12V DC power supply.

If you use a 21W lightbulb then your power supply has to provide at least 2A of current.

After you connect the power, the lightbulb should turn on.

Step 7: Enjoy Result

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39 Discussions

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samm008

3 days ago

I made your simple but very interesting project last night and it was fantastic. The sound quality is remarkably good and the sound level is big enough to hear from the adjoining room, even after the door is closed. But I did some changes to your original design to suit my expectations after doing some calculations and following trial and error method. I achieved the best result by the following changes,

I did not use 12V power but used only two 18650 batteries (about 7V) as I always prefer to use 18650 in my small projects. I replaced the light bulb with an 8.2 Ohm 7W wire wound resistor. Used a 4700 MFD capacitor to couple the speaker. Used two 3.3 kilo Ohm resistors to make the stereo sound source to the mono amplifier input.

Even at a fairly high volume level, two batteries ran for more than 4 hours to show a noticeable power loss. Heat generated by the resistor and MOSFET was hardly noticeable. Hoping to build the stereo version in the future.

This is truly a good project for kids and Tronics beginners.
Thanks for publishing this wonderful project.

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Chydzim

Question 11 days ago

I made something like this for stereo speakers. Why it doesn't work? :(

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JohnC430Chydzim

Answer 7 days ago

Your power supply and the speakers are more then enough for this project. The G-S threshold voltage for the IRF540 is between 2 and 4 volts. below this the transistor is shut off.
You need to make sure the input signal is not too high or the amp will start clipping and the sound will be distorted.
The light bulb is a good idea to get a high power resistor but its value is also very unstable. Also it should be a 12V light bulb (car brake lights etc) In the video at 3:12 you will notice that the light bulb is on before he connects the signal and another important item is: DONT forget the heatsink.
This is not intended to get Hi-Fi. it is a nice fun project to learn something about electronics. Good luck.

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ChydzimJohnC430

Reply 6 days ago

Actually, I'm new in electronics and I have made this circuit not to get a good quality audio, but to learn something new and turn on old speakers. The next step for me is better stereo amplifier which can handle my speakers. Do you have any circuit diagram like that which costs less than 10-15$? In diagram from this topic, the most expensive ones were MOSFET (~1,7$) and radiators (~1,5$).

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ElectricalProjectsChydzim

Answer 10 days ago

Hi, The circuit is Ok, it should work. How does it behave when you connect it to the power? First, make one channel work, and then add another channel. When you connect this circuit to power the light bulb should turn on (if it doesn't, test your light bulb, if the bulb is OK, then MOSFET is probably dead.)
If light bulb turns on after you connect the power then test your MOSFET more: Connect a piece of wire between "gate" and "source" (labeled as "G" and "S" on the circuit). After connecting the wire, the light bulb should turn off. If it doesn't turn off it means MOSFET is dead. Need more information to tell more...

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ChydzimElectricalProjects

Reply 10 days ago

I use 12V cable from an old 400W PC PSU to power the circuit. Maybe 12V for stereo is not enough? When I connect it to PSU, both light bulbs turn on, and speakers are doing funny noise for a split second (that's normal, it means they turned on). When I plug jack into phone, the same thing happens. But when I play the music, it plays from phone, not from speakers.

After connecting wire, bulbs turn off. So both MOSFETs are working properly. I will try to make it again on the breadboard, maybe I have just done something wrong.

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ElectricalProjectsChydzim

Reply 10 days ago

I got it now, your phone does not recognize this device for some reason... try adding for example 100 Ohms resistors after the audio jack, between ground and right channel and between ground and left channel... I think that maybe your phone needs some real load, that is why I suggest adding resistors. You need to make your phone recognize the audio jack as a device. You did everything correct, but your phone thinks that nothing is connected.

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ChydzimElectricalProjects

Reply 9 days ago

I forced the phone to play audio through jack, and... It works! But I think it's not enough for my speakers, because they are playing quietly (as for them), and I can hear that sound is not 100% clear. Is there a way to extend the circuit to fix it? I have 300W speakers.

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ElectricalProjectsChydzim

Reply 9 days ago

Well, this amplifier is not that powerful, you can try to increase power to some degree by connecting more powerful light bulbs, but then MOSFETs will produce even more heat (don't kill your MOSFETs). This is a simple circuit and of course it has its drawbacks. It is probably the best what you can achieve by using one transistor per channel. If you need something much more powerful then it will be way more complicated.
The main drawback of my circuit that it consumes power even when music is not played. Getting 300W is not that easy, btw, I was using 8 Watts speaker.

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ChydzimElectricalProjects

Reply 8 days ago

My further research have shown that sound's quality is good until I set the volume at ~80% or higher. What do you think is the highest light bulbs' power not to kill the MOSFETs? Or maybe I should go for stronger/better ones (if there are ones)? Sorry for so many questions, but it's actually my new hobby, so I'm newbie :)

Consuming power when music isn't playing is not a problem due to ON/OFF switch in PSU.

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ElectricalProjectsChydzim

Reply 8 days ago

I think there is no need for more powerful MOSFETs, IFR540N will probably handle even 100W light bulb, I think it is not reasonable to go beyond that. A good heat sink is important here.

Well, I am not good at explanations, but I can try. The light bulb charges the capacitor C2, and the MOSFET discharges it. When C2 charges the current flows through it in one direction and when it discharges the current flows in another direction. C2 is connected sequentially with the speaker, so the current flows through the speaker as well and it makes sound... this explanation assumes that you know what MOSFET does.
Suggestion for beginners: replace MOSFET and the light bulb with push-buttons (but never push them at the same time, otherwise it will be short circuit) press one button and then press another, and look how diaphragm of the loudspeaker moves, and in which direction. it should at least help to understand how it works.

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XTLElectricalProjects

Reply 7 days ago

So thelight bulb acts as a resistor. What does your measure as. About 4k ?

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JohnC430XTL

Reply 6 days ago

A 12V 20W light bulb cannot measure 4K. When it is cold the resistance is lower than when it is hot. So we calculate for when it is hot. V^2/R = 20 W. 12^2/20 = 7.2 Ohms.

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trekman

Question 7 days ago on Step 7

Can the light bulb be removed from the circuit?
What would the the power supply need to be if the light bulb is omitted?

1 answer
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ElectricalProjectstrekman

Answer 7 days ago

The light bulb is needed, it limits current, without it something definitely will go wrong. In theory, you can use a DC power supply that can limit its current, but such power supply also should not have capacitors connected on its output, and should very quickly react to curent change... well I've never seen something like that, so the lightbulb is probably the best what you can use here.
It is great if someone will improve the circuit, but frankly speaking, I don't know what else can be improved here. Next step is to use more transistor.