Make the most beautiful sound with the least money

How to use the least amount of money to make a good-sounding speaker has always been the goal pursued by "welder" enthusiasts. Recently, the author spent three or four hundred yuan to make a set of speakers, which received very good results.

1. Sound Source 

You can buy a second-hand computer optical drive for 100 yuan. The key is to make a power supply. The circuit is shown in Figure I. Because the optical drive driving current is relatively large (12V, SV are about 1A each), a transformer with a secondary of about 15V and 20W should be used for power supply. The rectifier should be a high-current IN54xx series. The three-terminal voltage regulator should be installed on a larger radiator (I chose a 8cm long 8cmx2cm door and window rectangular aluminum material as a radiator).

2. Power Amplifier

It is made by modifying the TA7240AP amplifier board in the radio recorder without spending a penny. This amplifier has moderate power, good sound, and low power consumption. I call it a "green" amplifier. TA7240AP is a dual-channel power amplifier integrated circuit that is widely used in domestic radio recorders. It has the characteristics of low distortion and complete protection circuits. The working voltage is 9~18V. The typical application circuit is shown in Figure 2. It is particularly worth mentioning that the volume potentiometer of this circuit uses the 50kΩx2 type with a middle tap, and an equal loudness circuit is installed:, thereby enhancing the audibility of this combination.

Although the power of this amplifier is slightly smaller, the sound is very pleasant to listen to when it is made according to this circuit. After comparison, I found that the effect is better than TDA2030 and discrete amplifier circuits within 100 yuan. This may be because the internal circuit of this integrated circuit is relatively mature!

3. Speakers

The total cost of the small-sized "Shock 6A" speaker box is 260 yuan (box 100 yuan, speaker unit 120 yuan, crossover 40 yuan). The Yindi YDQG5-2 is selected as the tweeter. This unit uses a soft silk diaphragm, magnetic fluid cooling, and a maximum power of 30W; the Yindi YD178-2P is selected as the woofer. The speaker diaphragm is a glue-coated paper cone, the sound is full and powerful, and the maximum power is 60W. The box costs 100 yuan and a skilled carpenter is asked to use 18mm thick medium-density fiberboard according to the size of "Shock 6A" (215mmx270mmx790mm), see Figure 3. The crossover uses the Huaxin brand HX5-10 model, and the circuit is shown in Figure 4. This speaker occupies a small area, but the bass effect is incomparable to the bookshelf box.

Although the above combination is not expensive, the sound quality is very encouraging. The overall feeling is that the sound is soft, full, elastic and very musical. This may be due to the TA7240AP and the equal loudness circuit realizing their "potential"!