4 Watt audio Amplifier


Posted on Apr 15, 2012

The circuit is very simple and incorporates darlington output transistors that will provide more than enough output current than is needed to drive a 3-ohm speaker. The gain may be pre-set for a variety of input levels, making it suitable for amplifying computer and cassette-deck Line-output levels. The input level is also suitable for use with the TDA7000 receiver. All components are easily available and I will shortly be making this project available as a kit. Naturally, the project will be built on a PCB which will also be available separately. Here is the first PCB, assembled and working.


4 Watt audio Amplifier
Click here to download the full size of the above Circuit.

The completed unit is 60mm x 75mm and only 30mm deep. The depth could be reduced to 10mm if the output capacitor is mounted at the speaker and the on-board electrolytics are mounted horisontally. Here are the typical performance figures that may be expected from the finished amplifer using a 3-ohm load with a 13.8-volt supply. No heatsinking is required for the output transistors when running at a modest output level with either speech or music. A small heatsink should be fitted to the two TIP41 transistors if running a constant tone level. The heatsink could be bolted directly to the TIP41s without electrical isolation if the heatsinks are not going to touch anything. A heatsink with a 15-square surface area is all that is required. Here is the circuit of the amplifer. The distortion and noise levels may increase at higher gain levels, but the test board was measured with Vgain = 10 and was driving a 3-ohm car Hi-Fi speaker. With higher-impedance speakers the frequency response will become wider but the output power will reduce a little. There was no trace of instability throughout the AF range and up to 150KHz so I thought it unncecssary to include a Zobel network. Incidentally, four-watts of AF will have the wife banging on the workshop walls, so do not underestimate QRP AF!




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Jakub K.   Apr 3, 2019

Hello , why are you leading 220uf through the 1K resistor into output? Whats the purpose? Thank you.

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