This article mainly introduces the idea of ​​self-made audio power filter, and describes in detail the practical application of self-made audio power filter.
Audio power filterThe audio power filter is divided into inductive and non-inductive. Generally, a non-inductive power filter is used, because the non-inductive filter suppresses the clutter current better, the output current is faster, the sound quality is wider, the details are richer, and the low-frequency dynamic extension is better.
The application of audio power filter has improved the sound quality of low-power appliances such as CD players, DVD players, pre-stages, etc., mainly in the background noise suppression. The application effect for car audio is also quite prominent. However, if it is used in high-end HIFI audio at home, it needs to be equipped with high-quality power filters. Improper configuration of ordinary power filters will restrict the current output and affect the effect. Applied to ordinary audio equipment, it can only make the sound cleaner more, and improving the sound quality more is just a psychological comfort.
For audio products, power supply is very important. It can even be said that the importance of audio equipment power supply cannot be overstated.
The author didn’t have a deep understanding of power supplies when I used to mount motorcycles. Later, after reading an article about power supplies written by Master Zhu in Hangzhou, I became interested in power supplies. Research and practice, and deeply feel that the motorcycle power supply and the surrounding system of the motorcycle power supply, such as the power supply filter and the power line, are the most effective methods of all the methods of the motorcycle power supply.
We know that in an audio equipment, the power supply is the foundation, just like the foundation of a building. If there is a problem with the foundation of a building, it is difficult to build the building. Even if it is built, a lot of remedial work will be required during the construction, and this remedial work has not seen good results. At present, domestic manufacturers are doing exactly the opposite. Take CD manufacturers for example. Most of them tend to ignore the power supply and focus on the DA conversion chip op amp. The manufacturers do this for their insidious purposes. . Because most domestic manufacturers are still unable to produce very good equipment themselves, they have to use conceptual speculation to attract people's attention. However, to speculate concepts, there is obviously more speculation in chips than speculation in power supplies. Just like the domestic computer manufacturers, they always use the CPU as a shame, but the supporting motherboards, hard drives and graphics cards are very poor, which leads to the fact that most domestic computer CPUs are used very well, but the overall performance is very poor.
There are several shortcomings in the power supply of domestic equipment, 1. Simple and backward design, 2. Cutting corners with materials. Listeners who often dissect foreign machines have the feeling that the circuit part of foreign famous devices is more complicated. The reason why they do not use the current "universal" circuit, but design their own power supply according to the requirements of their own equipment. The circuit lies in their deep understanding of the power supply. Among the domestic CDs, the power supply of Dongfang Voice is very unique. In addition to a large number of high-quality components on its power board, there are also a large number of inductances, which can output large currents. In addition, the DVD power supply with high degree is also more distinctive. When the machine provides positive and negative power, it does not use 7812 and 7912 like a through board, but uses two 7812, so that the output current is closer to the current output by the battery.
In the power supply part, the author is most interested in the practice of Hangzhou Master Zhu. Although the power supply we usually use in power amplifiers is also classified, this classification is incomplete. We know that the existing power supply part is first adjusted by a transformer, then through a diode, and then through a filter capacitor, and then the power is sent to the device to be used, but in this way, it is superficially grouped, in fact, due to the classification Not enough, there is still interference. This is like using one canal to irrigate many lands. The canal has many openings to water different lands. In this way, the water flowing into each plot must have a slow flow rate and the amount of water is not enough. In order to solve this problem, we had to use large transformers and high-capacity capacitors, but this can alleviate the current intensity problem, and there is still interference. Moreover, the power supply deviates far from linearity. Master Zhu’s approach is that each level of the power supply uses its own independent path. The power supply begins to subdivide the group in the transformer, and then the different power supplies after the step-down enter their independent filter circuits, and the filtered current directly reaches the power component. Each group of power supplies except for the common transformer, after coming out of the transformer Just part ways and don't interfere with each other. This is like using a special canal to irrigate each piece of land. Although digging ditches and occupying the land is laborious, the effect of irrigating the land will definitely be very good. And when Master Zhu chooses the filter capacitor, he does not use electrolytic capacitors, but connects a large number of EC capacitors in parallel to replace the filter capacitors. According to him, after rubbing the domestic ordinary power amplifier power supply in this way, the effect is very good and the homophony is rich. People think of 300B. However, it must be pointed out that Master Zhu’s design idea is correct, but it is difficult to operate, because EC capacitors are very expensive. In this way, the EC capacitor alone will cost 1,500 yuan. If the CD is used, the amount is It can be less. There is a workaround, which is to follow Master Zhu’s design, but replace the EC capacitors with other high-quality electrolytic capacitors (I will talk about the electrolytic capacitors of the power supply in Section 3). Now the author is working with an electronics factory to develop a high-quality and low-cost decoder. The power supply method used is like this. The electricity of all the electrical components is divided into independent groups, and finally each group of electricity is directly supplied to the electricity consumption. Place.
When we use filter capacitors for filtering, we often like to connect a small-capacity capacitor in parallel, so that high-frequency signals can have its own path, and this small capacitor should be connected in parallel at the root of the entire capacitor bank, which is the place closest to the circuit board. Inspired by this, I used the same series of capacitors with different capacities in parallel when using filter capacitors, such as 10u, 47u, 63u, 100u, 220u, 470u, 660u, and 1000u in parallel. One, the last one with large capacity can be used a few more to ensure capacity. This configuration allows signals of different frequencies to have their own dedicated channels. Of course, small-capacity capacitors should be placed in the front during specific installation, that is, the position closest to the circuit board. The capacitor I use is the RIFA124 series electrolytic capacitor, which can be called the best in the world. The effect is very good, but this method takes up too much space, and there must be a large space in the case before it can be used. If you install a low-capacity oil-immersed capacitor in the place closest to the circuit board, the effect will be better.
If there is a problem with the power supply design, it can be remedied to some extent by using suitable components. From the author's practice, the use of suitable components can greatly improve the sound quality. However, many domestically produced machines are very economical in terms of materials, which leads to the lack of seriousness in the power supply. Among the domestically-made machines, there is a manufacturer who has worked hard on the power supply, but his mind has turned crooked, and this manufacturer is original. Those who are familiar with original products know that its sound is relatively elegant, but in order to make the sound not bloated, and to make the sound more light, the manufacturer began to make a fuss about the power supply. The other components of the power supply section are very good. For example, ultra-fast diodes are used, and even a low-resistance LT317 is used, but the transformer only uses a 20-watt transformer. It achieves the purpose of reducing the sound by using low internal resistance and limiting current supply. In order to make the sound faster and not too bloated, the capacity of the filter capacitor is also low. The filter capacitor used to power the optical drive is 3300u. After I bought it, I found that this new machine was very serious. 15% of the disks could not be read. Check the Internet. I checked it and found that some users on the Internet also reported that original products were picking discs, but when I increased the capacity of the capacitor to 4000u, there was no more picking discs. Due to the lack of power supply, it sounds okay when playing small dynamic works, but the dynamics are slightly larger, and the machine immediately shows up. Therefore, when someone in this forum buys original A6 and A8, I always advise everyone not to buy it because of the machine. The power supply part is not so good.
Better results can also be achieved by taking certain measures on the periphery of the power supply. There are two main ways. One is to add a power filter and an isolation transformer, and the other is to use a better power cord.
According to my own practical experience, it is necessary to use a power filter. When you first use the filter, I just feel that the high frequency is better. The other benefits seem to be hard to find, but when you use the 3- When the filter is removed after 6 months, you will immediately feel that the sound leaving the power filter is very muddy, and at this moment you will feel how different the sound is after the power filter. There are external and built-in filters. Many filters on the market are long, with about 8 universal sockets on them. Among all the domestic filters, the AF-20 of Fengzhisheng left a deep impression on me. The body of this machine is very large, one can top the other 3, and the casing of this machine is very thick, even thicker than most power amplifier casings, and the weight is also very large, but the drawback is that the socket of this machine is not of national standard. , The American plug can no longer be used.
At present, most of the built-in filters are disassembled products, that is, second-hand goods, most of them are aluminum shells, and there are also copper shells. Although they are disassembled products, you can use them with confidence, because the components inside are basically high-quality Film capacitors, resistors and inductances are not easy to break. I install a built-in filter on each machine. The effect is even better than using a large external filter, but the price is higher. Much cheaper. There is also a built-in filter that is a socket type. Its appearance is slightly larger than that of ordinary sockets. The components are installed in the socket. The brand new price is between 6-12 yuan, but I still recommend buying a second-hand one with a sealed aluminum shell. Although the filter is second-hand, the effect is better than the new socket type.
It is absolutely necessary to equip the machine with a good power cord. Now I always have to take a look at the power cord when I listen to the equipment. But it is very rare to buy a good cord now, and most power cords on the market are not worth that money. I once saw a Xindak power cord in an electrical appliance store and asked the boss how much it was. The boss said it was 480. I looked up and said that you know what you are doing. I would buy it for 280. If you leave it to the manufacturer and merchant, I will buy it. , Then the cost of this line is actually very low. The current cables mainly use large plugs and wire diameters to scare people. The cables are made very thick with multi-layer shock absorbers, which makes people feel that it is very good. But in my practice, I don’t mean that a thick power cord is better than a thin sound. According to my practice, the reasonable combination of wires of different materials is a very simple method to obtain good sound. Of course, the reasonable use of magnetic rings and beads is also a very effective method. I will not say how to use it. If you supply power to CD and transistor equipment, I still recommend that you use Teflon silver-plated wire. The effect is very good. If the bass is not enough, you can combine 3 shares into one, of course, the cost will increase. If power is supplied to the electronic tube equipment, copper wires and wires of mixed materials are still used. The speed of the silver thread is relatively fast, the lines are very clear, but a little harder, the simplest way to improve is to make the oil thread. I will launch several power cables and signal cables as soon as possible. Naturally, they are oil cables, Teflon silver-plated materials, and clever use of magnetic rings, and strive to reduce the price of power cables below 300. The cheaper the better.
Another way is to use magnetic beads. You can put the wire on the wire or wind the wire around the magnetic ring first. Friends in Taiwan have a lot of experience in this regard.
Of course, improving the power supply can also directly lead the audio directly from the junction box, but our ordinary listeners have limited conditions, and those methods that we can't do will not be introduced.
Practical application of audio power filter1. Circuit description
This kit is a power amplifier centered on the integrated circuit TDA2030A. It has the characteristics of low distortion, few external components, simple assembly, high power, and high fidelity. It is very suitable for radio enthusiasts and audio enthusiasts to make themselves and students to assemble. In the circuit, D1—D4 are rectifier diodes, C11 is filter capacitor, C12 is high-frequency decoupling capacitor; RP1 is volume adjustment potentiometer; IC1 and IC2 are two-channel power amplifier integrated circuits; R1, R2, R3, C2 ( R7, R8, R9, C7) are the bias circuits at the input of the power amplifier IC. Since this circuit is powered by a single power supply, the circuit can work normally when the DC voltage at the input of the power amplifier IC is 1/2 the power supply voltage; R4, R5, C3 (R10 , R11, C8) constitute a negative feedback loop. Changing the size of R4 (R10) can change the feedback coefficient. C1 (C6) is the input coupling capacitor, C4 (C9) is the output coupling capacitor; when the circuit is connected with an inductive load speaker, R6, C5 (R12, C10) can ensure high-frequency stability. Signal flow: The audio signal is input from X1 through the volume potentiometer RP1, then coupled by C1 (C6), enters pin 1 of IC1 (IC2), amplified by the integrated circuit, output from pin 4, and arrives at the output coupling capacitor C4 (C9) X2.
2. Performance parameters
Input voltage: AC≤15V
Output power: Po=5W＋5W (RL=4Ω)
Output impedance: 4-8 Ω
Component list
Circuit diagram
The following content is the welding process
1. Look at the component list to see if there is any error in the number of component names. It is best to measure each component and confirm that it is correct before welding.
2. Weld the resistor and diode first
3. Welding signal input pin
4. Weld the terminal block, the signal output terminal block should be buckled together and then welded
5. Welding electrolytic capacitors and monolithic capacitors, monolithic capacitors are non-polar, electrolytic capacitors have polarity, and the shaded part on the circuit board is the negative electrode of the capacitor
6. Welding power supply filter capacitor and output coupling capacitor. Pay more attention to the polarity of these three capacitors. Reverse installation may cause the capacitor to overheat and burst.
7. Welding the volume potentiometer, the shell of the potentiometer should be connected with a "grounding" wire, as shown in the figure, when welding this wire, the shell of the potentiometer should be polished with a steel file to make the welding firm.
8. The effect of the "ground" wire on the potentiometer after welding
9. Finally, weld the heat sink and TDA2030A, so that the 2030 dual-channel amplifier kit is welded.
ConclusionThis is the end of the related introduction about the audio power filter. I hope this article can give you a deeper understanding of the audio power filter.
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