• We make a portable sound amplifier for headphones. Op-amp headphone amplifier circuit with double output current

    Introduction

    I’ll frankly say right away that this was my first audio amplifier, and this is my first such article, and if any of the more experienced and knowledgeable datagorians see the weak points of this project, please let me know about them, I will be very grateful!
    It all started with the fact that New Year I decided to give myself a small gift, namely headphones from a well-known German company. Since I’ve been listening to music all my life either through inexpensive Chinese multimedia speakers or in a Korean car, the new acquisition seemed like a fairy tale to me! I listened to music on my new headphones all evening long. Further - more, if “ears” for 50 bucks produce such sound quality that if I buy something more serious, I’ll be hooked!?
    After surfing the Internet, I found out that “serious” headphones have a resistance of more than 32 Ohms (which I considered the standard for all headphones), along the way I found out that for such instances it is better to acquire a special telephone UMZCH in order to unlock their potential. But buying an amplifier was not part of my plans. I’ll do it myself, I thought, since my profession is directly related to electronics.

    Rice. 4 Customized amplifier circuit

    I also corrected my signet, here is the final version - Fig. 5. I placed all the transistors under one heatsink (they still don’t get very hot), freeing up space for my modifications.


    Fig.5 Final version amplifier circuit board


    Two black paths are with reverse side boards (I cut them out with a knife after etching and drilling). The board turned out to be two-layer; otherwise it would not be wired normally; the size is 90x110 mm.

    Fig.6 Power supply diagram


    Several questions immediately arose:
    - why are there no film or ceramic capacitors in the rectifier?
    - is there any real benefit from capacitors in parallel with bridge diodes?
    - for what purpose were these particular resistor values ​​chosen in the stabilizer kit?
    I'll collect it and see, I thought. Well, in general - not a fountain. As I thought, without film capacitors in the rectifier, capacitors in parallel with the diodes in theory reduce the level of RF interference, but without them it’s not bad, I didn’t notice the difference either by ear or by instruments. But I liked the work of the stabilizer switching circuit, I should take note. When connecting the amplifier, a 100 Hz background was heard. I won’t spoil my experiments, the final circuit of the power supply, with my adjustments (Fig. 7)

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    Fig. 7 Power supply diagram with my adjustments


    Now I am satisfied with the power supply, the background noise from the headphones is gone. At maximum load(1A on both shoulders), the voltage at the output of the stabilizers drops by 10 mV.

    My signet in Fig. 8

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    Rice. 8 Power supply signet

    A ready-to-use power supply installed on the chassis is shown in Fig. 9.


    Rice. 9 Amplifier power supply

    A little about the design. The mole rat BP is made of double-sided 3 mm fiberglass, because after etching the tracks there was copper foil left on the back side, I decided not to tear it off (a nasty task), there will be additional shielding. One radiator for two stabilizers, again from the old one motherboard. On the right side of the board there is a connector for connecting a blue LED (for LEDs of a different color, you need to reduce the value of resistor R1, see Fig. 7). The output voltages are output through wires soldered directly into the board (blue harness in Fig. 9). The transformer is screwed to the board with an M6 pin. Board size 90x200 mm.

    Frame

    As always, the most time-consuming part of the project is the body. The case is completely dismountable (my specific requirement, whoever works in a sensitive enterprise will understand) is made of 2.5 mm aluminum and 3 mm fiberglass. M5 brass nuts are soldered to the rectangular fiberglass plate that serves as the chassis for the device. The power supply board is screwed to the chassis with 4 hexagonal posts and 2 screws (see Fig. 9). The amplifier board is screwed to the racks, the connector from the power supply is connected (Fig. 10.


    Fig. 10 Amplifier assembly.

    The front and back panels are made of sheet aluminum, bent on a machine. The top cover is made of fiberglass. Side panels made of aluminum are screwed at the end of the assembly to the corners on the chassis and on the top cover; they form peculiar legs.
    Assembled amplifier(Fig. 11) turned out to be completely shielded, screw connections ensure reliable electrical contact between the housing parts. Rear panel contains a standard 3-pin plug from a computer power supply, and a switch from there.


    Fig. 11 Assembled device

    I will briefly describe the important aspects of the assembly.

    1. All wires are twisted, and those that go from the power supply to the amplifier are shielded (just in case).
    2. IMPORTANT! The power supply housing is connected to the chassis at one point, where the transformer is screwed on (that’s why the pin securing the transformer is brass)
    3. IMPORTANT! The nuts of the headphone connectors on the front panel (the signal housing hangs on them) are insulated from the front panel with dielectric washers.
    4. The potentiometer shaft is electrically connected to the body of the device; if this is not done, touching the potentiometer shaft will cause interference in the headphones.
    The design turned out to be restrained. The body is painted with matte black spray paint (2 pieces were used for 3 layers). The handle on the potentiometer shaft is made from a perfume cap. All screws and ends of the side panels are polished to a mirror finish.

    Conclusion

    I am 200% satisfied with the amplifier. Huge power reserve, complete absence of background, by the way, there is no clap when turned on either, clear neutral sound, introducing no embellishments or artifacts into the sound path. I don’t even know what else you can expect from such a device.

    P.S.: I recently installed it in my amp instead of the NE5532, operational amplifier LM4562, and I realized that it could be better. As they say, there is no limit to perfection!

    If you have cool monitor ears and an old mobile phone with an MP3 player that is not able to “pump up” the headphones, then this article is for you!

    Actually, what is needed to assemble the amplifier:

    Minimum set:

    1. Micra itself TDA 2822(can also be modified 2822 M/S or its equivalent KA 2209)
    2. 4 electrolytic capacitor 16v – 100 mf(well, in general, Conders are like butter in porridge - bigger is better, but for 100 mf headphones there is an excellent size/quality ratio)
    3. Wiring is lighter, multi-colored 20-25 cm is enough for the head.
    4. Soldering iron and everything for soldering
    5. straight hands and a sober head are welcome :)

    Expanded set (optional):

    • headphone jack (can be torn from a Chinese radio)
    • small switch (from the same radio)
    • ferrite rings (can be torn out from amplifiers from “grid” antennas)
    • Textolite and everything for its etching
    • Old iron
    • Drill with thin drill bit

    laser printer, textolite and everything for etching it (if there is a desire for assembly on a board)

    Let's move on to the assembly: For those who don't want to bother with printed circuit boards, you can assemble the amplifier by surface mounting, that is, floating without a board, but the structure will be fragile and you will either have to hide it in a box or still assemble it on a board.

    We assemble using hinged installation according to the diagram

    To collect it on the board you will need textolite, first clean it with alcohol or any other degreasing liquid and set it to dry.

    Having drawn it, we simply copy our diagram several times.

    I do this so that after transferring it to textolite, I can choose the most successful version and etch it so as not to print it again.

    We trim the edges so that they do not interfere with us.

    It is advisable not to touch the side where there is a seal.

    Next, we apply the printed side of the paper to the cleaned side of the PCB and press it all down with a heated iron (set the iron to max) for 20 - 25 seconds. Do not think that holding it for a long time will make the toner better; on the contrary, it will become brittle and crumble.

    As the paper gets wet, remove the paper with light circular movements using kind of balls.

    Once again, thoroughly rinse the board (to remove any lint).

    Next, we dilute a solution of ferric chloride (sold on radio markets). Sorry, but at that moment the charge on my body died..... and I was too lazy to wait for it to charge when the CJ solution was already cooling down...
    We throw our board into the solution.

    The etching time depends on the temperature of the liquid and its saturation with liquid liquid.

    Nevertheless, the board after etching looks like this:

    We wash off the toner from the tracks and tin (for those who are in the tank, we cover it with a layer of tin) it.

    Before tinning I coat the board
    After this, the board can be tinned perfectly with an alcohol-rosin solution. The photo clearly shows how terrible my board looks, all because when I washed off the toner after etching, I rubbed it a couple of times with sandpaper, so that some of the tracks were torn in places, and so that there was no break in the circuit, I left a thick layer of tin (but when it’s thinner it still looks more beautiful). Next we punch holes and assemble.

    I think there will be no further problems. The photo shows that the microcircuit is installed on the side of the tracks, this is not entirely correct, I did this because we came across a lot of non-working microchips on the market and it was not very convenient to solder them on the other side (you would tear the track or something else) I had to pervert . I use this amplifier for computer ears, it is invisible, so I didn’t try very hard to make it beautiful.

    Every novice radio amateur, after the first successful experiments, having felt the sweetness of his victories, wants to try to do something real. Not a toy, but a real working full-fledged thing. A simple homemade one that can be assembled with skillful hands in just a few minutes is perfect for this.

    Where can it be used? Firstly, for its intended purpose, namely to amplify the signal from a tone control unit or preamplifier, that is, where it is too weak and impossible to connect headphones. In this case, you can make a headphone amplifier with your own hands.

    Secondly, it will be useful as an additional tool. A portable headphone amplifier is quite suitable for testing circuits. After all, it often becomes necessary to find the place where the signal breaks in new scheme, which you collected, but it just doesn’t want to work. For example, you made the same headphone amplifier with your own hands. It will help in finding the cause of the malfunction. With it you can very quickly find the point where the signal disappears. After all, this often happens because of a trifle: a part is poorly soldered, a faulty capacitor, etc. It can be difficult to find the cause visually or using a tester.

    Making a headphone amplifier with your own hands is easy, because the mono circuit consists of only five parts. It is based on the TDA7050 chip, which costs 30-80 rubles. But I think that in your stocks of radio components, which anyone who is passionate about this business always has, there will be such a microcircuit. It was often used in cassette players and other simple devices reproducing sound.

    Using the same chip, you can make a stereo headphone amplifier with your own hands. To do this, you will have to add two polar capacitors to the output (one common one is possible), and the input can be made from a double

    The microcircuit itself is in a package normal size(DIP8). Operating supply voltage is from 1.6 to 6 volts. Doesn't consume much energy. The output signal power depends on the supply voltage. In the stereo version, with a load of 32 ohms and a voltage of three volts, you will get about 130 milliwatts of output on each channel. When connected via a bridge circuit in the mono version, the power is doubled. The output of the microcircuit is protected from

    Schematic diagram is given in Figure 1. The input signal is supplied to pins 1 and 3, and 32 Ohm headphones are connected to pins 7 and 8. According to technical conditions, in bridge mode the load should not be less than 32 Ohms. To smooth the voltage, capacitors C1 and C2, 100 and 0.1 μF, respectively, are connected to the power bus. The resistance of resistor R1 is 22 kOhm. Well, that’s probably all the description of our first model.

    The second circuit from Figure 3 is often used in small-sized factory-made devices. It's not much more difficult to make it. The diagram shows all the necessary details. Figure 2 shows the same diagram for connecting speakers. As you can see, the difference is small. The speaker circuit uses polar capacitors in each output channel, and for headphones - it costs common capacitor at the point where the circuit housing is connected to them.

    Dissatisfaction with playback quality musical compositions sound card computer forced me to start making a desktop amplifier. I decided it would be simple. homemade amplifier for headphones, assembled according to the classical scheme on one .

    However, there is a note. This amplifier is suitable only when input signal does not require voltage amplification (for example, an MP3 player or computer provides a sufficient output). Also, any noise generated in the power supply will go straight through the amplifier. For this reason, it is necessary to use only a stabilized power supply. Output voltage range 10-20V and current 750mA. Here we use an N-channel MOS transistor with reverse diode for work in key and linear mode IRF610. During the manufacturing process of the amplifier, the use of other transistors was tested: IRF510, IRF611, IRF612 and IRF710, all without exception worked well. I recommend not using IRF530 and IRF540 (commonly found in power supplies). The used LM317 stabilizer with adjustable output voltage allows you to very accurately adjust the output parameters of the power supply.

    Since this amplifier will be sitting on a desk in a production office, it needs to fit in with the work environment. I was lucky that there was a failed external CD-ROM, its design was perfect. In addition, its case already had a switch, power adapter, RCA socket and inputs on the rear panel, as well as a headphone jack on the front panel.

    In the manufacture of the amplifier, only those electronic components and components that were available. Conventional resistors and film capacitors. Capacitors with a capacity of 1 µF, 0.47 µF and 0.1 µF are polypropylene. But no one is stopping you from using higher quality parts.

    Cooling radiators have a relatively small volume of cooling area, but I draw your attention to the fact that they are screwed directly to the metal body, which also takes part in heat dissipation. The smaller radiator has a volume of approximately 1.75 square inches. Be sure to isolate the MOSFET and regulator from the heatsinks.

    The operation of the amplifier was tested using adjustable block power supply, it turned on at low voltage. The bias is set using a 100 kOhm variable resistor. The amplifier showed good job throughout the entire voltage range from 10 to 20 V, but still high-quality sound reproduction began at a supply voltage of more than 13 volts.

    Next, the operation of the amplifier was checked at USB help oscilloscope. This is DSO-2150 with 60 MHz throughput And maximum frequency sampling rate 150 μ/s. The sine wave we saw showed itself at its best from 20 Hz to 20 kHz.

    Square wave 100 Hz

    Square 4800 Hz

    Green is the input signal, and yellow is the output. The signal power of my generator is not high and this is reflected in the quality of the original waves. If you compare the input voltage and output voltage you will see that the circuit gain is about 0.8. It can be seen that at 100 Hz there is a slight slope. The slope gradually decreases and the frequency increases and beyond about 300 Hz the squared wave response is excellent up to 20 kHz - the limit of the oscillator signal. Since the music consists mostly of sine waves this is not a problem. Since an MP-3 player or computer will be used to adjust the volume, there is no need for a potentiometer. Another ULF, but using lamps, is possible.


    I’ve been wanting to make a separate headphone amplifier for a long time - I haven’t had the time, although I’ve already bought headphones for two years. Nothing special, Sennheiser HD 558, but the sound is at an acceptable level for me.
    I reviewed a lot of diagrams and read a lot of information and forums. I wanted the circuit to be simple and of high-quality sound. Thinking about what I wanted, I came to the conclusion that the headphones needed relatively little power and some kind of op-amp powered by transistors or just a powerful op-amp with a low THD+N, a “driver” so to speak, should be suitable. And then a microchip from TI turned up, specially designed for these purposes, TPA6120.

    At its core, it is a very powerful and very fast op-amp with a monstrously low THD+N (well, at least for me). Having surfed a little on Google about various microcircuit inclusions and designs, I found a good option for myself on one website of Czech radio amateur Pavel Ruzicka. The microphone is connected using a non-inverting circuit, with a 50 kOhm potentiometer from the well-known Japanese company ALPS at the input. I decided to implement just this option.

    Headphone amplifier circuit based on TPA6120 and power supply


    My version of the scheme



    power unit


    After studying the datasheet on the TPA6120, I still made some changes to the circuit. The so-called blocking capacitors are originally film capacitors, but the datasheet strongly recommends using SMD ceramic capacitors, and also as close as possible to the power terminals - to eliminate possible excitation of the amplifier.
    As a matter of fact, I was most excited and afraid, the microcircuit is very fast-acting.

    That dreaded PowerPAD has been defeated.

    Due to the lack of experience in manufacturing double-sided PCBs, it was decided to make the board single-sided. And then another problem emerged. Due to the fact that the microchip is very powerful for its size, it has a heat sink pad on its “belly” - PowerPAD, which is soldered to the pad under the microcircuit and also serves as a common wire.
    I somehow brushed aside the unpleasant thoughts and decided that I would solder it somehow. But first things first.

    I started looking for the necessary components, and it immediately became clear that the locals didn’t have the TPA6120, not to mention the ALPS. The Great Chinese Brother helps out once again, he ordered a TPA6120 chip and an ALPS potentiometer on Aliexpress.
    I bought the housing, transformer and other small items from the locals. After everything was in hand, another 4 months passed before I picked up... an iron.


    When designing the amplifier board, I paid special attention to the location of the resistors in accordance with the datasheet, so that there were the shortest distances from the legs of the inputs and outputs to the resistors, so that there was no excitation. And now the boards are etched, drilled and tinned. And here I seriously began to think about how to solder this tricky PowerPAD and what to do with it in general.


    Back on the Internet. I found an interesting solution on one of the forums. Without a soldering gun and double-sided PCB with metalized holes, there is only one way out: drill a hole under the microcircuit and through it try to solder a homemade radiator to the PowerPAD of the microcircuit.

    I tried this suggested option: drill a 1.5 mm hole, take copper wire, tin and wind it in a spiral around a 0.8 mm drill (I wound it around a needle) 2-3 cm long. The microcircuit is positioned and grabbed, the spiral is lowered into the hole and the whole thing is fried with a 40-watt soldering iron, naturally with the addition of solder and flux. The goal is not just to solder the spiral, but also to ensure that the edges of the PowerPAD pad are also soldered to printed circuit board.


    Here it is, my cooling system for the TPA6120. Do you see the strange “spring” in the center?


    I held the soldering iron for a few seconds and everything worked out! Everything turned out to be simpler than I thought. Thank you good man for the idea!

    Sound

    The boards are ready, I connect everything with wires, quick check. There is no constant output, I connect my DAC, Senheisers, turn on “The Dark Side Of The Moon” and enjoy... Probably, describing the sound and especially its quality is a thankless task, you just have to hear it for yourself.
    In general, I will say that I really liked the sound throughout the entire frequency range. By ear there is a minimum of distortion, for me there is simply none. I used to listen to mine Sennheiser headphones HD 558 with built-in sound card. Now I simply didn’t recognize them! Bass appeared and the sound was very detailed.

    Total

    Us sings. There is no excitement, and thank God, fortunately, all measures were taken for this. I doubted that the coil would dissipate heat well, so I left it for an hour with music at a decent volume, touched the microcoil - it felt like 30-35 degrees. The coil is warm, the pad on the reverse side is also slightly warm, which means the microcoil is soldered normally, the heat is dissipated well, and that’s where I calmed down.


    And the most difficult and painful thing for me began - to collect everything into the case. A couple of evenings with a drill, pliers, screwdrivers, files and a lot of obscene language! Hurray, I stuffed the boards into the case. The case turned out to be too big for the amplifier, but it is convenient to mount and looks more solid in a large box. There is only one task left: to make inscriptions on the front panel. But that's a completely different story.
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