This is the circuit design of 21W class AB audio amplifier uses power transistors as the main part. It is a simple design, and simple to set up. Set the 10k trimmer to about half way and the 470 ohm trimmer to 0 resistance. Power up and set the quiescent current to 30mA by trimming the 470 ohm trimmer. Once done, measure the offset voltage. Trim the 10k so that between -30 and 30mV is measured. The amplifier should now be able to pump out just over 21W.

Technical Data:

Frequency response: 2Hz – 17kHz flat
THD: Once again, very low (I haven’t measured it yet). It won’t be audible
Gain: 29.87dB (600mV for 21W into 8 ohms)

The gain can be modified by changing the 100k feedback resistor to a 470k resistor and the 10k in series with the input to a 33k. This will increase the input impedance significantly and the new gain will be 21.58dB (~1.6V input for 21W into 8 ohms). This suits my application for the amp. Just remember that changing these resistors will change the output offset voltage, so if you’re going to experiment by changing the feedback loop, do it with a cheap, single driver speaker if you’re experimenting with a speaker connected. Also readjust the offset and quiescent current!

Power Supply for 21W Class AB audio Amplifier Circuit

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As you can see on the circuit, this class AB amplifier IC requires only a few external components. And this 10 W audio amplifier circuit is also very easy to build. This 10W stereo amplifier circuit requires a stable power supply with a voltage of 18 V and 1A current needs.

High quality 10W Audio Amplifier parts list :

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On figure 1 is a simple, inverting amplifier with class AB output signal amplitude value 1 kV, which uses two identical amplifying cells. Frequency response amplifier gain full located in the region from DC to 20 kHz.

You can provide gain and higher frequencies, but at a lower value of gain. Ratio of resistors R1 and R2 set the gain. This scheme eliminates the need for multiple components to the level shifts, which are commonly used in standard construction of the scheme. Positive and negative cells gain controlled in opposite phase.

Resistors R4 and R5, connected to the source of 15 V and -15 V, provide the required voltage shift guarantee always on the state of the output transistors. Fine tuning the value of resistors R4 and R5 can eliminate distortion output signal of the “step”. Zener D1 and D2 provides reverse bias photodiodes magnitude 6.2 V.

Resistors R10, R11, R12, and R13 form a local negative feedback to the output transistors. You must install four STW8N80 N-channel MOSFET transistor with a suitable heat sink to prevent overheating. The scheme does not require active protection against short circuits. One pair of 125 mA fuse high-voltage power lines is enough to protect circuits from damage.

Above shows the response to the scheme on a square wave of 10 kHz. The signal has no distortion at the top of the pulse and the front and rear edges are virtually identical. Below pic shown on the scheme in response to sine wave frequency of 20 kHz. Signal in both figures has an amplitude of 1 kV.

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