It can provide much more simply by increasing the power supply voltage. The available output power is limited by the power supply. Up to 70 watts output has been achieved with this topology.
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 shows that I have used polarized capacitors. Modern op-amps,with the same pin-out as the op-amps shown in the schematic, can be used in the pre-amp portion
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