Low power circuit and headphone amplifier designed by NE5532
The NE5532 has been in existence for several years since its introduction. Everyone is very familiar with its circuit and has a variety of gameplay. The amp described here is characterized by simplicity, low power, and a focus on the manufacturing process.
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Speaking of low-power amps, I have to mention the NE5532 of the 20th century op amp, which has appeared in countless excellent preamplifiers and tuning circuits. The intermediate frequency is warm and delicate, bold and cost-effective! Until today we can easily find it in some low-end audio products. Because of its small size and simple circuit, it is the first choice for practical and low-input hands-on.
First, the principle analysis NE5532 is a typical bipolar input operational amplifier, a small power circuit composed of a single NE5532 has many versions, I have constantly modified and thought, to modify those various circuit diagrams, and finally determine the schematic ( figure 1). The magnification is controlled by R3(R4) and R5(R6). Theoretically, if R3(R4) is 1kΩ and R5(R6) is 100kΩ, the magnification is 100 times, but for the amp, This will cause self-excitation, and even if it can really reach 100 times, the effect is not good, so this circuit is best not to be adjusted to 100 times when used in the pre-stage. Of course, for the amp to be 2 to 3 times, the negative feedback can be moderate, the sound quality is soft, clear and transparent, but the magnification can not be too small, otherwise it will affect the sound quality, you can repeatedly debug to achieve your own satisfactory results. The author sets R3 (R4) to 1kΩ and R5 (R6) to 20kΩ, which is 2 times. C5 (C6) is the ground path of the input loop. It should be increased when used in the amp circuit. The value in the schematic is 22 uF, but it should be increased to 100 uF for this amp. 
It is worth mentioning here that the power supply problem, if you are using the regulated power supply, pay attention to the filter of the regulated power supply, because the circuit itself is very simple, then the selection of components is more critical, it is recommended When selecting materials, try to choose components with better quality.
Second, PCB drawing The author used Protel 99 SE for wiring design. The PCB picture (Figure 2) that everyone saw is the third version of my painting. It is also my most satisfying version. The first few versions have flying lines. There is no such version, and there are problems with flying lines in many versions of the Internet. This is not tolerated by the discerning hands-on. Due to the small area, it is necessary to strive for a little grounding in the grounding, and the input and output terminals can also be modified according to the actual situation. Leave all the components in a space, neatly aligned, and look very harmonious. 
Third, the choice of materials for the selection of materials, I believe that friends everywhere have different channels, because the author in the main city of Chongqing, components are better to buy, this time in addition to buying new components, but also bought some old tonic, used Less than 10 yuan.
1. Polar capacitor: choose brand ELNA, C1 (C2) select 10 uF/50V, C5 (C6) select 100 uF/50V, C9 (C10) can choose 47 uF ~ 220 uF. I have used 47 uF for the third edition, which has no effect. You can change it yourself.
2. Non-polar capacitors: the best pairing when buying, I chose the second-hand German WIMA and Swedish EVOX white square MMK film capacitors. C3 (C4) is 200 pF (or 220 pF) and C7 (C8) is 0.1 uF.
3. NE5532: NE5532, which is produced by American Signetics Company, is commonly known as the Big S5532. It is one of the best sound producers in the production of 5532 (has been discontinued for many years) and is the first of the four ace amplifiers of the year. I only found second-hand ones. If you can't find them, you can choose PHILIP. Of course, Tao Feng is also good.
4. All the resistors are all made of five-ring metal film resistors. The domestic Dahongpao that I have collected is also used, and will not be detailed.
5. The copper clad laminate used in the circuit is a scrap of the crucible. (I heard that people used to use it for TV circuit boards, I believe it will not be very bad, and the thickness is enough).
Fourth, after the preparation is sufficient, the PCB is made. There are many methods for hand-made plates, such as a special stereotype machine (available in qualified schools, the cost is high, but the quality of the plate is also the highest). The commonly used methods are Photosensitive plate and thermal transfer. Since the material on hand is limited, the thermal transfer method is used. It is recommended that everyone: after the PCB has been corroded and dried, it is best to punch the hole first, then polish it with sandpaper, and then apply a solution of rosin to alcohol, which can both weld and prevent oxidation.
After the PCB is completed, the soldering can be started. The principle is to first solder the resistor and then solder the capacitor. The soldering is completed after three times and five divisions. It is worth reminding that: my PCB input and output are the plug-ins selected, but in practice, because of the outer casing, I did not solder the plug-in directly on the PCB. Friends who have the material and strong hands-on ability can do it themselves. Make a shell.
Five Beautification Appearance After the welding is completed, first debug, after the previous method is satisfactory, it will be boxed. I rummaged through the cabinet and finally found a box. It was a metal box when I bought a USB flash drive. There was a transparent window on it to make a viewing window. When I placed it, I took it and punched it. Many friends like to listen to pure tone, there is no use of volume potentiometer, so I did not draw on the board, if a friend wants to add a volume potentiometer like the author, the potentiometer is double 50kΩ, the connection is very simple.
Power supply, the voltage of friends who like to use the regulated power supply should be adjusted to double 15V effect will be very good, I use two 9V dry batteries, mainly for convenience.
Cover the box, this small amp can be taken away, the effect is much better than the previous one, and the sound range is wider, the sound quality is softer. Such a simple circuit, interested friends may wish to try.
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