Here is a reliably high sound quality audio power amplifier project based on the National Semiconductor’s LM1875 IC.
The circuit that we give is a similar form of the application circuit in the datasheet that NS provides. It is really easy to build and low cost.
The voltage gain of the each monolithic channel is 27dB but you can change this value by adjusting the resistors at the feedback path that connects the pin-2 and pin-4.
The supply voltage for the maximum power output (25 Watts) is +/- 25V. It mustn’t exceed +/- 30V at any time. We recommend you to use metal film resistors and electrolytic capacitors that are rated at 50V.