20 Watt Stereo Audio Power Amplifier by LM1875

Description:

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.

Mini Metronome by 555 Timer/Oscillator IC

This mini metronome gives a linear scaled output and 40 to 208 beats per minute.

Circuit Operation: 1- Q1 and Q2 transistors provide linear frequency variation of IC1 depending on the changes of P1 value. 2- Q3 amplifies the click sound output and gives louder beats. 3- To provide a higher output , a 12V micro battery is used. It also makes the circuitry more compact. 4- Rotate the P1 potentiometer fully towards R2, then set R1 to obtain 40 beats per minute by the help of another metronome.