Here is a simple 10-watt audio amplifier using IC LM1875. The IC has five pins and can deliver a maximum of 18-watt output power depending upon the supply voltage and load. The author’s prototype is shown in Fig. 1.
Circuit and working
The circuit diagram of the audio amplifier is shown in Fig. 2. It is built around popular amplifier LM1875 (IC1), an 8-ohm, 10-watt speaker (LS1) and a few other components.
Connect the audio input from your mobile/laptop/PC to CON1. Connect 15V battery and switch on S1. You should hear amplified sound in speaker LS1.
Construction and testing
Use a 25-watt soldering iron for soldering LM1875 and other components. A 2-pin connector should be used for input and output connections to make the prototype safe and clean. Use a suitable heat-sink for LM1875 to prevent its overheating.
An actual-size, PCB layout for the amplifier is shown in Fig. 3 and its components layout in Fig. 4. After assembling the circuit on the PCB, enclose it in a suitable box. Fix LS1 on the rear side of the box.
For testing the circuit, connect a 6V battery to this circuit along with an 8-ohm, 10-watt speaker.
Take a metal screwdriver and gently touch at the input terminal. If your prototype is working, you will hear a humming sound from the speaker. You may connect a 100-kilo-ohm potmeter between audio input and ground and middle pin of potmeter to pin 1 for volume control. Your circuit is now ready to use.
You can use the power supply from a 5V to 15V battery, which will give you clear and noise-free audio signal output.
The LM1875 is a monolithic power amplifier offering very low distortion and high-quality performance for consumer audio applications.
The LM1875 delivers 20 watts into a 4Ω or 8Ω load on ±25V supplies. Using an 8Ω load and ±30V supplies, over 30 watts of power may be delivered. The amplifier is designed to operate with a minimum of external components. Device overload protection consists of both internal current limit and thermal shutdown.