Simple and practical small amplifier

Because of its convenience in carrying, easy operation and good sound quality, Walkman is favored by music lovers in school. However, Walkman is powered by low DC power supply (such as 1.5V, 2V, 3V, etc.), and the output power is small.

For this purpose, a simple small power amplifier with an output power of up to 1W is specially designed, which has the functions of equal loudness, noise reduction, volume and tone control, and has low cost. The circuit schematic is shown in the figure below.

In the figure, RL is a matching resistor, and its value should be consistent with the nominal load of the Walkman to ensure that the output stage circuit of the Walkman works in the best working state. C3, C4, W2 and C1, C2, W1 are the volume control and equal loudness circuits of the left and right channels respectively, and have a certain inhibitory effect on high-frequency noise. R5~R8, W5, W6, C9-C12 and R1~R4, W3, W4, C5~C8 respectively constitute a simple left and right channel tone control circuit. R13NR16, G14 and R9NR12, C13 respectively constitute a simple noise reduction circuit and low-pass filter for the left and right channels. With the clever combination of the tone control circuit, a signal waveform close to that during recording can be obtained at the input end of TDA2822, so that the fidelity can be improved. R18 and R20 are output protection resistors, which are used to prevent TDA2822 from being damaged due to a short circuit to the ground at the output end. R22, LED1, leg D2, etc. Overcurrent indication circuit, when the working current of the power amplifier is greater than 400mA, LED1 and LED2 will light up. Cl3 and C14 are input DC isolation coupling capacitors, and high-quality electrolytic capacitors with extremely wet drain should be used to facilitate the smooth passage of audio signals without blocking signals. C17 and Cl8 are the ground paths for input playback, which are usually 10μF or 47μF in typical circuits. If the input impedance is too large, it will cause signal blocking or self-excitation. Here, C17 and Cl8 are increased to 100 douF, and the sound quality is improved and the sound range is widened. C26 and C27 are output DC isolation coupling capacitors, which are usually selected as 220μF. This makes the output impedance appear too high, signal blocking, causing distortion, and even self-excitation. Now C26 and C27 are increased to 680μF, and the sound quality is significantly improved, and the sound range is also widened.

This circuit can work normally as long as it is installed correctly and the quality of the components does not need to be debugged.