Circuit diagram of low power headphone amplifier made with NE5532

Speaking of low-power headphone amplifiers, we have to mention the NE5532, the king of op amps in the 20th century. It has appeared in countless excellent preamplifiers and tuning circuits. The intermediate frequency is warm, delicate and thick, full of courage, and very cost-effective! To this day we can easily find it in some mid- to low-end audio products. Because of its small size and simple circuit, it is the first choice for those who value practicality and low investment. Because NE5532 has been around for several years since its introduction, everyone is very familiar with its circuit and has a variety of ways to play it. The amp introduced here is characterized by simplicity, low power, and emphasis on the production process.

1. Principle analysis

NE5532 is a typical bipolar input operational amplifier. There are many versions of low-power circuits composed of a single NE5532. Through constant comparison and thinking, I modified those various circuit diagrams and finally determined the schematic diagram (Figure 1). The amplification factor is controlled by R3 (R4) and R5 (R6). Theoretically, if R3 (R4) is 1kΩ and R5 (R6) is 100kΩ, the amplification factor is 100 times, but for the headphone amplifier, This will cause self-excitation, and even if it can really reach 100 times, the effect will not be good, so when this circuit is used in the preamplifier, it is best not to adjust it to 100 times. Of course, setting the headphone amplifier at 2 to 3 times can provide the right amount of negative feedback, softer, clearer and more transparent sound quality, but the amplification factor cannot be too small, otherwise it will also affect the sound quality. You can debug it repeatedly to achieve the effect you are satisfied with. The author sets R3 (R4) as 1kΩ and R5 (R6) as 20 kΩ, which is 2 times. C5 (C6) is the ground path of the input circuit and should be increased when used in an amp circuit. The value in the schematic diagram is 22 uF, but it should be increased to 100 uF when used in this amp circuit.

What is worth mentioning here is the power supply issue. If you are using a regulated power supply, you should pay attention to the filtering of the regulated power supply. Because the circuit itself is very simple, the selection of components will be picky. It is recommended that When selecting materials, try to choose components with better quality.

2. PCB drawing

The author uses Protel 99 SE for wiring design. The PCB diagram you see (Figure 2) is the third version I drew, and it is also the version I am most satisfied with. There are flying lines in the previous versions, and this version is No, many versions on the Internet have the problem of flying cables, which cannot be tolerated by picky hands-on people. Due to the small area, try to get some grounding when it comes to grounding, and the input and output terminals can also be changed according to the actual situation. Leave space for all components, arrange them neatly, and look harmonious.

3. Material selection

Regarding the selection of materials, I believe friends from all over the country have different channels. Because the author is in the main urban area of ​​Chongqing, it is easier to purchase components. This time, in addition to buying new components, I also bought some old supplements, which cost less than 10 yuan. .

1. Polar capacitor: Choose the brand ELNA, choose 10 uF/50V for C1 (C2), 100 uF/50V for C5 (C6), and 47 uF ~ 220 uF for C9 (C10). I use 47 uF in all three versions, it has no impact, everyone can change it by themselves.

2. Non-polar capacitors: It is best to match them when purchasing. 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: Use the NE5532 produced by the American Signetics company, commonly known as the big S5532. It is the best-sounding one among the many manufacturers of 5532 (it has been discontinued for many years). It is the first of the four ace op amps of the year. The author only found second-hand ones. If you can’t find them, you can also choose the PHILIP ones. Of course, the Taofeng ones are also good.

4. All resistors must use five-ring metal film resistors. The domestic Dahongpao in my collection is also used, so I won’t go into details.

5. The copper-clad laminate used for the circuit is scrap scraps (I heard that others used it to make TV circuit boards. I believe it will not be bad and the thickness is enough).

4. Processing

After being fully prepared, it’s time to make PCBs. There are many methods for manual board making, such as special molding machines (available only in schools with qualified conditions, high cost, but the quality of board making is also the highest). Commonly used methods include photosensitive board making. and heat transfer. Since the materials on hand were limited, I used thermal transfer printing. Here is a suggestion: after the PCB is corroded and dried, it is best to drill holes first, then polish them with sandpaper, and then apply a solution of rosin and alcohol, which can not only help soldering but also prevent oxidation.

After the PCB is ready, you can start welding. The principle is to solder the resistor first, then the capacitor, and the welding is completed. It is worth reminding: I use this kind of plug-in for my PCB input and output, but in practice, because of the shell, I did not solder the plug-in directly on the PCB. Friends who have the materials and strong hands-on ability can do it themselves. Make a crust.

Five beautify the appearance

After the welding is completed, debug it first. After debugging is satisfactory according to the previous method, it is time to pack it. After rummaging through boxes and cabinets, I finally found a box. It was a metal packaging box from when I bought a USB flash drive. There was a transparent window on it for viewing. I arranged the location and punched holes. Many friends like to listen to pure tone and do not use the volume potentiometer, so I did not draw it on the board. If any friend wants to add a volume potentiometer like the author, the potentiometer is double 50kΩ, and the connection method is very simple.

In terms of power supply, those who like to use a regulated power supply should adjust the voltage to about double 15V for good results. The author uses two 9V dry batteries, mainly for convenience.

Close the box and this little amp is ready to go, sounding much better than anything previously made, with a wider range and a softer sound. Friends who are interested may wish to try such a simple circuit.