NE5532 designed small power circuit and headphone amplifier

The NE5532 has gone through several years from its launch to the present, and everyone is very familiar with its circuits, and has a variety of ways to play it. The characteristics of the amp introduced here are simple, low power, and focus on the manufacturing process.

When it comes to low-power amps, I have to mention the NE5532, the emperor of the 20th century. It has appeared in countless excellent pre-amplifier and tuning circuits. The mid-frequency is warm and delicate, full of boldness, and the price is very high! 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.

1. Principle analysis NE5532 is a typical bipolar input operational amplifier. There are many versions of a small power circuit composed of a single NE5532. I have made constant comparisons and thoughts to modify the various circuit diagrams, and finally determined the schematic diagram ( figure 1). The magnification is controlled by R3 (R4) and R5 (R6). In theory, if R3 (R4) is 1kΩ and R5 (R6) is 100kΩ, the magnification is 100 times, but for the amp, This will cause self-excitation. Besides, even if it can achieve 100 times, the effect may not be good, so it is best not to adjust this circuit to 100 times when used in the pre-stage. Of course, 2-3 times the amp can make the amount of negative feedback moderate, the sound quality soft, clear and more 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. I set 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 diagram is 22 uF, but it should be increased to 100 uF for this amp.

It is worth mentioning here is the problem of power supply. If you are using a regulated power supply, pay attention to the filtering of the regulated power supply. Because the circuit itself is very simple, the selection of components is more picky. It is recommended to When selecting materials, try to choose components with better quality.
Second, the PCB drawing author uses Protel 99 SE for wiring design. The PCB picture (Figure 2) you see is the third version of my drawing and the most satisfactory version. The first few versions have flying wires, and This version is not available, and many versions on the Internet have the problem of flying lines, which is not tolerated by the discerning hands-on. Due to the small area, it is necessary to strive for a little grounding in terms of grounding. The input and output terminals can also be modified according to the actual situation. Leave all the components with space, neatly arranged, and look very harmonious.

3. Material selection For the selection of materials, I believe that friends from all over the world have different channels, because the author is in the main urban area of ​​Chongqing, the components are better purchased, this time in addition to buying new components, I also bought some old supplements, used Less than 10 yuan.
1. Polarity capacitor: choose brand ELNA, C1 (C2) choose 10 uF / 50V, C5 (C6) choose 100 uF / 50V, C9 (C10) can choose 47 uF ~ 220 uF. I use 47 uF in all three editions, no effect, you can change it yourself.
2. Non-polar capacitors: It is best to pair them at the time of purchase. The author chose second-hand German WIMA and Swedish EVOX white square MMK film capacitors. C3 (C4) is 200pF (or 220pF), and C7 (C8) is 0.1 uF.
3. NE5532: The NE5532 produced by the American SigneTIcs company, commonly known as the big S5532, is the best-sounding one among many manufacturers producing 5532 (it has been discontinued for many years), and was the first of the four ace op amps that year. I only found second-hand ones. If you ca n’t find them, you can choose PHILIP. Of course, the pottery seals are also good.
4. All the resistors use five-ring metal film resistors, and the domestically produced Dahongpao collected by the author is also used, which will not be described in detail.
5. The copper clad laminates used for circuits are scraps of picking up (I heard that others used to be used for TV circuit boards, I believe it will not be bad, and the thickness is enough).
Fourth, after the preparation is fully prepared, it is time to make PCBs. There are many methods for manual board making, such as special engraving machines (only available in conditional schools, high cost, but the quality of the board is also the highest), commonly used methods are Photosensitive plate and thermal transfer. Because the materials on hand are limited, I use the method of thermal transfer. Here I suggest everyone: After the PCB is corroded and dried, it is best to punch holes first, then polish with sandpaper, and then apply a solution of rosin to alcohol, which can both help soldering and prevent oxidation.
After the PCB is ready, you can start soldering. The principle is to solder the resistor first and then the capacitor. It is worth reminding: my PCB input and output are the selected plug-ins, but in practice, because of the shell, I did not solder the plug-in directly on the PCB. Friends who have materials and strong hands-on ability can do it by themselves. Make a shell.
Five beautification appearance After welding is completed, first debug, after the debugging is satisfactory according to the previous method, it is time to pack. Turning over the box and turning over the cabinet, I finally found a box, which was the metal packing box when I bought the U disk. There was a transparent window on the top to make a viewing window. Many friends like to listen to pure tone, they don't use volume potentiometer, so I didn't draw on the board. If a friend wants to add a volume potentiometer like the author, the potentiometer is double 50kΩ, the connection method is very simple.
In terms of power supply, the voltage of a friend who likes to use a regulated power supply should be adjusted to about 15V. The effect will be very good. The author uses two 9V dry batteries, mainly for convenience.
Cover the box, and this small amp can take over and take over. Its effect is much better than the previous production, and the sound range is wider and the sound quality is softer. Such a simple circuit, friends who are interested may wish to try.

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