Active speaker is an organic combination of power amplifier and passive speaker, which is widely used in multimedia. Active speakers save the power amplifier shell, save space, reduce external lines, and eliminate the functions and circuits (such as karaoke circuits, etc.) that are repeated with VCD and other audio sources, especially the power amplifier and the speaker achieve a better match, so they have a higher Cost-effective. The author refers to relevant information and makes many active speakers. Now I will briefly introduce one of them, for readers' reference.
Active speakers are not a simple combination of power amplifier and passive speakers. The following three issues need to be considered when designing: (1) The selection of speakers. Floor-standing speakers are large in size, easy to place power amplifier components inside, and have a good frequency response, so they are suitable for selection. (2) Selection of power amplifier circuit. Considering the problem of heat dissipation, choose Class A and B amplifiers. Amplifiers made with discrete components need to install a speaker protection circuit, and the relays in the relays will cause malfunction due to the sound of the speaker and affect the performance, so it is not suitable for high power. The excellent performance of the integrated amplifier circuit, such as LM1875, TDA1514A and TDA1521, has perfect overvoltage, overheat and short circuit protection functions, fully meet the requirements of active speaker power amplifier. (3) A speaker is used as the "main speaker", and the input and output connector panel and radiator are installed on the rear panel. Place the transformer and power amplifier circuit in their boxes. Connect one output directly to the speaker (frequency divider) in the main speaker box, and the other power output to another speaker through the panel terminal.
1. Amplifier production Ten years ago, power integrated circuits were mainly used in low-end combined audio. With the maturity of integrated circuit technology, many high-power integrated circuits with excellent performance, stability, and reliability are widely used in audio power amplifiers, and have achieved good results. Effect. I have made integrated circuit power amplifiers such as TDA1514A, LM1875 and TDA1521, etc. The sound quality, as described in many articles, can reach the level of fever and have its own characteristics. Now introduce the TDA1521 integrated circuit power amplifier, because this circuit is a high-fidelity (Hi-Fi) two-channel monolithic 2 × 15W power integrated circuit produced by Philips. It is characterized by extremely simple peripheral circuits (some peripheral circuit components have been designed and manufactured in integrated Within the block), is a "fool" integrated circuit (see Figure 1). The author composed its dual channels into a BTL circuit with an output power of up to 40W, which can be used as the main channel power amplifier circuit for AV power amplifiers (see Figure 2). If the two channels are used separately, the output power is 2 × 15W, which can be used as the center channel and surround channel power amplifier circuits. Therefore, this integrated circuit is very suitable for amateur production by radio enthusiasts.
| Some readers may think that the power of the TDA1521 power amplifier is too small, because many articles introduce that the power of the main channel should be more than 2 × 50W, and the power of other channels also requires more than 30W. The author believes that the general home listening room is about 14-20m2, the room volume is about 40-60m3, and the music power is usually 1/10 of the total power (that is, the power has a margin of 10 times), then the main channel There is a 2 × 4W output, which is large enough. Therefore, as long as the power has a certain margin, it should not be blindly pursuing big, otherwise it will increase costs and cause unnecessary waste. The author mainly considers that the power amplifier is matched with high-quality audio sources such as VCD, and the output voltage of the VCD audio source is higher, so the pre-amplification part can be omitted. The amplifier does not have a tone control circuit, allowing high-quality sound sources to pass through the amplifier without artificial modification, which is also a requirement of high fidelity. The small capacitor in the circuit selects CBB model, the 1Ω resistor selects NEC five-color ring resistance, and the double-connect potentiometer selects ALPS type. Transformer 150W, EI type core. The radiator is made of single-sided teeth, model DL176, and the heat dissipation area is 1300cm2. See Figure 3 for the arrangement of components on the connector panel. The blackened surface of the contact area between the heat sink and the two integrated circuits should be scraped off and coated with thermal grease to reduce thermal resistance. |
| The power amplifier part includes the power amplifier circuit board, radiator, transformer, connector panel and wiring. After the power amplifier part is made, it can generally be powered on for audition without debugging. After normal audition, it is assembled with the speaker. 2. Box production and assembly The box adopts 15mm thick medium density board, and the inverted structure is used. The manufacturing method is the same as that of the passive speaker (see Figure 4 for dimensions), and will not be repeated here. The difference is that one of the speakers as the main speaker should be treated as follows: (1) Two holes should be opened on the rear panel for the installation of the panel and the radiator, and the size of the opening is smaller than each side of the panel and the radiator 1cm, easy to fix the screw. (2) Four supporting wooden blocks are placed in the box for placing transformers. The transformer is placed at a distance from the speaker and close to the inverter hole. |
| When assembling, first fix the transformer, and then fix the panel and radiator from the outside of the back box plate to the back box plate, and put a layer of 2mm thick soft rubber pad on the contact place to ensure the seal. The heat dissipation teeth of the radiator are outward, which is convenient for heat dissipation. Finally, fix the speakers and crossover. The frequency divider is a self-made two-way 6dBLC frequency divider. The speakers are selected from the South Whale brand. One YDQG20-8G8Ω80W and three YD165-8XP8Ω50W speakers are included in each box. LC divider output. |
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