[Photo] Micro active power amplifier

Computer active speakers sold on the market are huge in size and single in function, and the prices are all above one hundred yuan. The active speakers on the computer do not have too high requirements for sound quality, and are generally used for learning multimedia educational discs. The author recently made a cheap computer active speaker, which not only satisfies the above-mentioned functions, but also can be built into the case. A volume switch can control the on and off of the speaker and the power supply and the volume.

working principle:

TDA2002 is an audio power amplifier integrated circuit (Figure 1 ). It can output about 3W of undistorted power on an 8- ohm load. It has a variety of internal protection circuits, which are strong against abnormal conditions such as current surge, overvoltage and load short circuit. Adaptability, working voltage 8-18V , The quiescent current is 4 mA, which was very popular in the past few years. It is widely used for power amplification of surround channels. If you were an audiophile, you might have a few pieces on hand. Figure 2 refers to the typical wiring diagram of TDA2002 and connects to an audio power amplifier. In the figure, C2 is the input Coupling capacitor, which plays the role of coupling the audio signal while blocking the DC component. I didn't connect to C2 at the beginning , so there was a strong exchange sound from the speaker. C1 is also an input coupling capacitor, which isolates the audio signal of the sound card to the volume potentiometer. The volume potentiometer uses a commonly used 4.7K potentiometer with a switch . When the volume is turned to the minimum, the power switch can be turned off. C7 and C6 are power supply filter capacitors, which can filter and store the 12V voltage provided by the computer's switching power supply . C7 is helpful to reduce the high-frequency internal resistance of the power supply. The internal interference of the computer is very large, and audio interference will be generated when the switching power supply and digital circuit work. In order to improve the signal-to-noise ratio of the active speaker, the pass band of the audio amplifier can be reduced; C8 can bypass some high-frequency noise and improve Noise ratio.

Commissioning and installation:

When working in TDA2002 , you need to install a 10 * 10 (cm) aluminum heat sink, and apply an appropriate amount of thermal grease to facilitate heat dissipation. After the circuit assembly is completed, first connect an external 12V regulated power supply to turn on the volume potentiometer to the maximum. At this time, the speaker will emit a slight soft: "sand" current sound, when the speaker touches the signal input terminal, the speaker will emit a loud " "Woo" hum, which shows that the circuit is working properly. Connect the audio signal output from the sound card to the input terminal of the power amplifier with a double-core shielded wire, and then find an unused four-hole power plug, connect the 12V positive power supply ground wire to the power terminal of the power amplifier, and the volume potentiometer can be fixed At the panel of the computer case. Generally, the chassis has an idle full-high CD reserved position, which is usually covered with a plastic baffle, and the potentiometer can be fixed at the plastic baffle.

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