DIY Class a Amplifier





Introduction: DIY Class a Amplifier

About: Eletronic, robotics and physics lover

Hi, today I will share with you my little amplifier, is not very powerful but I love it.

Step 1:

You need:

1x Power bank

1x IRF3205

1x 275k,

1x 0,1k

1x 450k

1x 37Ohm

2x 2200uF

1x 100nF




Jumper wires

Step 2:

In the schematic we can see the 37Ohm resistor that has a power of 2W, the other are 1/8W and are enough critical, you should see a voltage of 2,5V across the big resistor if all works correctly.

This is a class A amplifier and use a power n-mos as a switch, but is not very efficient, so the power mos need a heat sink because is get warm quickly as the big resistor.

A 0,1k resistor in parallel to the speaker will give a less inductor and a more resistive load.

Step 3:

I haven't used a clean audio source file, but I hope you like it, bye.



    • Water Contest

      Water Contest
    • Oil Contest

      Oil Contest
    • Creative Misuse Contest

      Creative Misuse Contest

    4 Discussions


    6 months ago

    Amplifiers are so easy to make. And discrete components can be used to build one as well. But if you wanted a small package amp that works very well with very few components, try an LM386 IC and see how that works for you. It can be fitted into a really small package with lots of power. Even works great for a headphone amp.

    1 reply

    Seems very handy chip, thank you

    In the 1960s when power transistors were new and expensive, a Class A amplifier wasn't unusual to find in hobby periodicals. They were simple and inexpensive, and very fun to operate just like the amplifier you built and love.

    Back then, though, the speaker was connected where you have the 33 Ohm resistor. The thinking then was that if you have to waste power when there is no signal, you may as well dissipate it in the speaker coil instead of a resistor. I built your circuit using two 270K Ohm resistors and the speaker in place of the 33 Ohm resistor. Just 5 components. With 0.35Vpp input, the output power from the speaker was almost 1W. Extremely loud.

    The disadvantage is that with no signal, the speaker coil heats up so a power rating of 1W or better is required.

    I'm assuming you used a 0.1uF input coupling capacitor so that your music source wouldn't overload the amplifier. Some of the signal is dropped by the capacitor so that a volume control or resistor divider isn't needed.

    If it's of interest to you, try the changes I described above and see if your "not very powerful" amplifier doesn't blow the doors off. Your amplifier is better than you think :)


    1 reply

    Very good, but I'm still afraid about dc voltage across the speaker that can blow it and the spring effect of the diaphragm of the speaker, more powerful in one side, less in the other, anyway thank you very much I'm glad you like it.