The power transistors must be fitted on a heatsink! They have their collectors electrically connected so you don't have to isolate each other. The heatsink should have an area of at least 40 square centimeters. Note that the heatsink voltage is neither ground or supply voltage so do not connect it with anything else besides transistors. Be careful not to connect it with chassis ground. If you build the other channel for stereo use, do not electrically connect the heatsinks of both left and right channels.
|Single channel schematic|
The maximum output power is delivered without distortion with a 5 mVp-p input signal. A LTspice simulation proves ~ 2.5 W medium output power.
|Amplifier simulation in LTspice|
|Built stereo amplifier|
Downloads: LTspice and ExpressPCB files | PCB as PDF.