This is an AB class audio power amplifier which is based on the TDA2009. The circuit is a bridge-type amplifier, as described in the TDA2009 datasheet from ST microelectronics.
The amplifier can be powered from 12 to 14V and it may deliver up to 18W in a 2 ohm load, or up to 12W or 8W at 4 ohm or 8 ohm, respectively. An Overload at the output (even if it is permanent), or an excessive ambient temperature can be easily withstood. The TDA2009A can also withstand an accidental short circuit from the output and ground made by a wrong connection during normal operation.
The power dissipated in the circuit must be re-moved by adding an external heatsink to the TDA2009. Between the heatsink and the package it is better to insert a layer of silicon grease, to optimize the thermal contact All resistors in this circuit, apart from R1, R11 and R12, are of 1/4W type. R1 must withstand up to 2W and R11 and R12 are resistors of 1/2W type.
The circuit can be easily assembled and soldered in the printed circuit board provided below. Assembly instructions are also provided in figure 2. The PCB is very small. Its actual size is 51x56mm.
The amplifier circuit is mono. This means that to make a stereo amplifier you should use two identical circuits, one for the right and one for the left audio channel, respectively.
PCB artwork for the 18W audio amplifier