The audio amplifier shown below provides 14 watts of power, but can provide much more simply by increasing the power supply voltage. This amp was built in 1975 and has worked reliably ever since. The power amp portion was published in Popular Electronics in the mid-1975s. I added a preamp and bass and treble controls. This amp has extremely low distortion and is relatively insensitive to the choice of components.
The power amplifier is actually a discrete power op-amp. As such the gain is set by R18/R23. The pre-amp has a voltage gain of 10, for an overall gain of approximately 150. I recommend non-polarized capacitors for C2 and C9, even though the schematic show