Using discarded circuit boards to make small speakers

Electronics enthusiasts have a lot of discarded circuit boards. They have used discarded circuit boards to assemble many small speakers below 10W. The circuit shown in the figure below is very suitable for connecting to audio signal sources such as satellite TV receivers, DVDs, and EVDs. Under the conditions of a main power supply of +17V and a load of 4Ω, the power output is more than 5W, which is good for a small home theater and listening to disc music.

　　
The circuit boards and components in the frame were all disassembled from discarded color TVs, obsolete VCDs, scrapped amplifiers, and unwanted telephones.

The specific method is: find out the input, output, power supply and ground of the required circuit board, draw a reserved range (slightly larger), then carefully saw it with a hacksaw, grind the edges and shape it, and drill the fixing holes. Try to install the rectification and filtering circuits of the power supply in the blank space of the power amplifier board.

Although the power amplifier part on many circuit boards can be used, a dual-channel power amplifier with large output power and beautiful sound quality should be preferred. The output capacitor should be replaced with 1000μF, and the components that affect the frequency response characteristics and total gain should also be adjusted, and the heat sink of the power amplifier IC should be enlarged.

In waste amplifiers and VCDs, there are usually independent RC4558 amplifier boards, which can be cut and reused. MIC amplifier boards and MIC sockets can be cut and reused. There are also various potentiometer boards. The specifications of small capacitors and resistors on telephone circuit boards are the most complete.

The tone adjustment and signal input attenuation distribution circuits are designed by me. All resistors and capacitors are soldered on the potentiometers and signal sockets (see the picture below).

　　
When transmitting small signals over long distances, shielded cables should be used. For other connections, thicker cables should be used where necessary, thinner cables should be used where necessary, and shorter cables should be used where necessary.

+17V and +8V voltages are obtained by using a black and white TV power transformer with a center tap on the secondary side and a rectifier filter circuit (see the figure below). Its power is greater than 40VA.

　　
The transformer and AC wiring should be kept away from the signal input part. Each grounding point should be determined by actual test, with the AC interference noise minimized.

Although making small speakers requires a lot of thought and effort, the joy of success is endless.