High quality headphone amplifier circuit. Headphone amplifier on a specialized chip TPA6120. Actually what is needed to collect the amplifier

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

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

Secondly, it will come in handy as an additional tool. A portable headphone amplifier is quite applicable for testing circuits. After all, it often becomes necessary to find the place where the signal breaks in new scheme, which you have collected, but it does not want to work in any way. For example, you made the same headphone amplifier with your own hands. He will help in finding the cause of the malfunction. With it, you can very quickly find the point at which the signal disappears. After all, this often happens because of a trifle: a part was badly soldered, a faulty capacitor, etc. Visually or with a tester, the cause can be difficult to find.

Making a headphone amplifier with your own hands is simple, 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 is such a microcircuit. It was often used in cassette players and other simple devices reproducing sound.

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

The microcircuit itself is in a normal size package (DIP8). Operating supply voltage from 1.6 to 6 volts. Consumes not much energy. The power of the output signal 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 against

circuit diagram is given in Figure 1. The input signal is applied to pins 1 and 3, and headphones in 32 ohms are connected to pins 7 and 8. According to the specifications in bridged mode, the load should not be less than 32 ohms. To smooth the voltage, capacitors C1 and C2, 100 and 0.1 uF, respectively, are connected to the power bus. The resistance of the resistor R1 is 22 kOhm. Well, that's probably the whole description of our first model.

The second circuit in Figure 3 is often used in small-sized factory-made devices. Make it a little harder. The diagram shows all the necessary details. Figure 2 - the same diagram for connecting speakers. As you can see, the difference is small. In the circuit for speakers, polar capacitors are used in each output channel, and for headphones, there is a common capacitor at the point where the circuit case is connected to them.

If you are the proud owner tube amplifier, then, most likely, if you want to listen to your favorite songs alone, through headphones, you are faced with the inconvenience caused by the lack of an output to the headphones.

Yes, and the owners of expensive or not very smartphones and tablets also have a hard time - these devices are most often not able to shake quality high-impedance headphones. Therefore, your favorite compositions do not sound at all the same as on professional equipment.

Of course, if you are a true music lover and you value music more than money, then nothing will stop you from buying a $6,000 preamplifier, a $5,000 headphone amplifier, and $2,000 headphones themselves. And immerse yourself in nirvana... However, if the money situation is not so rosy, or you like to do everything yourself, then it turns out that you can assemble a high-quality headphone amplifier for only... 30$.

Why do you need him???

Do you need a precision amplifier? It depends on your musical tastes and habits. If you are used to listening to music "on the run", that is, from portable devices while walking, jogging, gym and other similar places, then the project described below is not for you. Just try to choose the most suitable headphones for your device in terms of characteristics and sound.

The same should be done if you love musical styles where there is strong signal distortion, such as rock, heavy metal, and the like.

However, if you prefer to listen to music in a quiet, comfortable environment at home or in the office, and your tastes gravitate towards live and natural music such as classical, jazz, or clean vocals, then you will be able to appreciate the sound quality and accuracy of the link. precision amplifier plus high quality headphones.

Options

Let's say you decide that you need a headphone amplifier. What's the next step? On the Internet you can find a lot of projects using the ubiquitous LM386. The microcircuit became popular due to its high reliability, low cost, ability to work with single supply and a small number of external elements. Such amps usually do well with inexpensive headphones, but all these advantages pale in comparison to the level of noise and distortion of the LM386 and a well-designed amplifier based on discrete elements or on special microcircuits.

If you have about $ 30 and are not afraid of working with surface mount elements (SMD elements), then the project presented here is exactly what you need.

Ideas and scheme

When designing this scheme, the following points were taken into account:

• The amplifier should be driven from the relative high-impedance output of a tube preamp or electric guitar amp. In other words, the input impedance must be easily adjustable for sources with different output impedances.
• a small number of components. Therefore, microcircuits were chosen instead of transistors.
• small amplification and power. Required to rock sensitive dynamic headphones and not the speaker system.
• The amplifier must be able to handle high-impedance headphones. The author uses a Sennheiser HD 600 (300 ohm resistance).
• achieve the lowest possible noise and distortion.

circuit diagram precision headphone amplifier shown in the figure:

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When developing this design, microcircuits from such manufacturers as National Semiconductor, Texas Instruments and others were considered. Weight useful information was found on Headwize resources and DiyAudio forums.

As a result, the choice fell on a precision headphone driver from Texas Instruments. TPA6120A2 And operational amplifiers AD8610 from Analog Devices for the input buffer.

The circuit turned out to be relatively simple, with bipolar power. If you are sure that there is no constant component at the output of your signal source, then the coupling capacitors (C24 and C30) can be excluded from the path using jumpers H1 and H2.

The power supply provides ± 12V at the output voltage at a load of up to 1A. Its scheme is shown in the figure:

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Often in audiophile designs, the cost of the power supply is several times higher than the cost of the amplifying part itself. It turned out a little better here - the cost of elements for the power supply is about $ 50 and the most expensive elements here are a transformer and electrolytic capacitors. You can save some money by replacing toroidal transformer to a conventional W-shaped, abandon the LEDs and fuses at the output of the unit.

A version with separate regulators for each channel TPA6120A2 was tested (the microcircuit has separate power outputs for each channel). The difference could not be heard or measured, which made it possible to significantly simplify the power supply.

Since all microcircuits used in the amplifier have low sensitivity to noise and interference in the power circuits, as well as high level suppression of common mode noise, then the use of typical power supply integral stabilizers turned out to be sufficient to obtain high performance.

TPA6120A2

The TPA6120A2 IC from Texas Instruments is a high quality, high fidelity headphone amplifier. It uses an amplifier architecture with differential input, single-ended output, and current feedback. It is thanks to the latter to a greater extent that low distortion and noise, a wide frequency band, and high speed are obtained.

The microcircuit contains two independent channels with separate power outputs. Each channel has the following characteristics:

• output power 80 mW into a load of 600 ohms at ± 12V power supply at distortion + noise 0,00014%
• more than 120 dB dynamic range
• signal/noise level 120 dB
• supply voltage range: ± 5V to ± 15V
• output voltage slew rate 1300V/µs
• protection from short circuit and overheating

For comparison, the level of distortion + noise for the "folk" LM386 chip is 0.2%. Although, of course, high parameters still do not guarantee high-quality sound. To obtain the maximum result, it is necessary to take into account the manufacturer's recommendations for the choice of external elements and topology. printed circuit board. All this can be found in the technical documentation for this chip.

AD8610

The AD8610 chip from Analog Devices is an operational amplifier with field effect transistors at the input, resulting in low offset and drift voltages, low level noise, low input currents. In terms of noise level and slew rate, these op amps are in perfect harmony with the TPA6120A2.

However, do not be lazy and try to replace them with other op-amps. The pinout of the AD8610 is compatible with other audiophile ICs. Moreover, many music lovers claim that they hear the difference in the sound of the op-amp!

Passive Components

Not all resistors are the same! And if your budget allows, use metal film resistors in this design, which are somewhat more expensive, but have lower noise and higher stability. If you want to save money, metal-film resistors should be installed at least in the input circuits (for the AD8610), where the sensitivity to noise is the highest.

It is better to put film capacitors on the signal path C23, C24, C29, C30. The manufacturer recommends ceramic capacitors for power circuits of microcircuits.

The main requirement for signal connectors is reliable contact. In his design, the author used the usual "jack" to connect headphones and gold-plated RCA-connectors with Teflon insulation to connect the signal cable.

The circuit diagram shows an amplifier version for operation from a tube preamplifier in which volume is controlled. If the design is supposed to be made more flexible and universal, then, of course, it is desirable to provide its own volume control at the input. To achieve maximum quality and in order not to degrade the characteristics of the amplifier, a high-quality potentiometer should be used here.

A budget version might be Alpha or RadioShack for about $3. For $40, you can already purchase an audiophile-grade product from ALPS. The best solution would be to use a hard disk attenuator from DACT or GoldPoint. Their cost is approximately $170. By the way, you can find similar Chinese-made attenuators on eBay for only $30. The value of the potentiometer can be in the range of 25-50 kOhm. The use of a step attenuator, in addition to the convenience of adjusting the volume, additionally guarantees the identity of the adjustment in both stereo channels, which is especially important in a headphone amplifier.

Design

All structural elements (except for the power transformer) are placed on one printed circuit board. If you decide to use an external power supply or assemble it in a different way, about 70% of the printed circuit board will remain free.

The layout of the elements is shown in the figure:

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The figure shows a drawing of the printed circuit board from the side of the parts:

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The figure shows a drawing of the bottom side of the printed circuit board:

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Drawings of printed circuit boards in the popular SLayout format can be picked up

The main feature of the installation: on the bottom side of the TPA6120A2 case there is a contact area of ​​approximately 3x4mm. She must be soldered to the area on the printed circuit board under the microcircuit, which serves as a heat sink.

Photo of the finished structure:

When you first turn on, you should remove the two fuses at the output of the power supply and make sure it works. If the output voltages are correct, replace the fuses. The amplifier itself does not need adjustment.

You can place the board in a case of suitable dimensions, preferably metal for shielding from external interference.

Conclusion

Subjectively, the amplifier sounds on par with professional studio equipment. Compared to the LM386, this design showed a smoother, clearer and more detailed sound.

The scheme turned out to be quite flexible and easily customizable for various needs. So, for example, the author himself assembled two copies of the amplifier. One according to the above scheme for operation in conjunction with a tube preamplifier. The second copy was designed to work with a smartphone and a guitar amplifier, so it was supplemented at the input with a high-frequency noise filter and a volume control. In addition, to increase the gain (the smartphone gave out an insufficient signal level), the values ​​of the resistors R6 and R14 were changed to 2 kOhm.

By changing the values ​​of these resistors, you can change the gain over a wide range.

A variant of the amplifier printed circuit board from our “Martian friends”, designed for installation of elements in “standard” packages (there are no DIP packages used in the design of microcircuits):

Animated demonstration of the board from all angles

from available materials. Everyone knows the situation when you need to turn up the volume a little. For example, from a phone or computer, so that you can comfortably listen to music or talk. The problem is that it is not always possible to find a low-power amplifier on sale that could meet your needs. Therefore, you need to make it yourself. Thankfully, this is very easy to do.

transistor design

It will turn out to be simple, but finicky - a lot depends on the parameters of the resistors and capacitors used in the design. In addition, the transistor circuit will be quite cumbersome. But it's not that scary. As a rule, the simplest two-stage amplifier circuit is used, in which there are only two transistors. Often this is CT 315 or similar. These transistors have gained popularity among radio amateurs. You can make absolutely everything from them, including a headphone amplifier with your own hands.

But there are drawbacks to such structures. It is necessary to accurately select the supply voltages of the emitter, base and collector. Please note that two types of voltages are suitable for the base, for example:

1. Positive (through resistance from plus supply).
2. Negative (through resistance from minus power).

The main thing is to accurately select the resistors in order to provide the minimum required voltage value at the base.

Chip amplifier

The above design is quite demanding in terms of nutrition. More than 5 volts is needed for it to work stably. But if you use a small chip, for example, TDA 2822, you will get following characteristics devices:

1. The supply voltage can fluctuate in the range: from 1.8 to 15 V.
2. Output power - no more than 1.5 watts.

And the whole structure will fit on a small printed circuit board. The case of the device will be very small - about a little more than two AA batteries, which will be used to power the entire circuit. In addition, small speakers can be connected to this amplifier. He will easily work with them.

Amplifier Parts

To make a high-quality and simple headphone amplifier, you need the following materials:

1. Chip - TDA 2822.
2. Variable resistor - 10 kOhm.
3. Constant denominations of 4.7 kOhm - 2 pieces; 10 kOhm - 1.
4. Electrolytic capacitors 10 uF - 2 units.
5. Film capacitors (non-polar) with a capacity of 100 nF - 3 pieces.
6. Two sockets - 3.5 mm.
7. Batteries.
8. A small piece of foil material.
9. Suitable body.

Outline the location of the parts on the board and draw the tracks. Cover them with varnish or use a printout of the picture on laser printer. This should be discussed separately.

Printed circuit board

The main thing is to make a printed circuit board. Only in this case will it work stably and efficiently portable amplifier for headphones. You can make a high-quality board with your own hands without much difficulty. To do this, you need a program for drawing such devices. You can even, in the absence of such, use the standard Paint application. It is only important to comply with all sizes. Draw the location of the tracks and conclusions of all elements, then you need to print the resulting image on glossy paper.

This is where various prospectuses come in handy, which are given out for free on the street and in stores. Print with the maximum degree of boldness. The paper should be saturated with toner. To make a DIY headphone amplifier, you need a quality board. Therefore, fasten glossy paper from the side of the foil so that it fits snugly. A well-heated iron should be driven for several minutes on the board. This will cause the toner and paper to adhere to the foil. Of course, the board must be degreased before starting work. That's all. Now it remains only to get rid of the paper. warm water wash it off, and the toner remains on the surface of the foil.

Prepare a solution of ferric chloride. This best option for etching printed circuit boards. Immerse your workpiece in the solution - in a few minutes all excess copper will be destroyed (if the concentration of the solution is good). If not, you'll have to wait. After drilling holes for the elements, cover the tracks with tin and proceed with the installation. The last step is connecting the power wires. Do this only after you are sure that the installation is correct.

Introduction

Rice. 4 Amplifier circuit corrected for itself

I also corrected my signet, here is the final version - fig.5. I put all the transistors under one radiator (they still don’t heat up much), freed up space for my improvements.

Fig. 5 The final version of the amplifier circuit board

Fig.6 Power supply diagram

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Fig. 7 Power supply circuit with my adjustments

My seal in fig. 8

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Rice. 8 Signet power supply

The ready-to-work power supply unit 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, copper foil remained on the reverse side, I decided not to tear it off (nasty occupation), 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 the resistor R1, see Fig. 7). Output voltages are output through wires soldered directly to the board (blue cable in Fig. 9). The transformer is screwed to the board with an M6 pin. Board size 90x200 mm.

Frame

Fig. 10 Assembly of the amplifier.

The front and back panels are made from machine-bent aluminum sheet. The top cover is made of fiberglass. The aluminum side panels are screwed at the end of the assembly to the corners on the chassis and on the top cover, they form a kind of legs.
The assembled amplifier (Fig. 11) turned out to be completely shielded, screw connections provide reliable electrical contact between the body parts. The back panel contains a standard 3-pin plug from a computer PSU, 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 (therefore, the stud that secures the transformer is brass)
3. IMPORTANT! The nuts of the headphone jacks on the front panel (the signal housing hangs on them) are isolated from the front panel by dielectric washers.
4. The potentiometer shaft is electrically connected to the body of the device, if this is not done, when touching the potentiometer shaft, there will be interference in the headphones.

Not all sound cards can provide loud and high-quality sound, and then a headphone amplifier will come to your aid. The reason for assembling a headphone amplifier may be insufficient volume (the main reason), or poor sound quality (large distortion in sound / music). To increase the volume and sound quality, simply connect an additional output stage in series with the sound card, which we see in the diagram below:

The harmonic coefficient with a linear frequency response from 20 Hertz to 20 kHz of such an amplifier is only 0.1% and such an amplifier can be used not only for a computer sound card, but also for low-power devices such as radio, mobile phone, mp3 players, laptops and netbooks.

Now consider the power supply to power the amplifier. If you are going to power from the mains, then you will definitely need to assemble a power supply unit (power supply). The transformer is any small secondary current of at least 250 mA and a secondary voltage of 16-24 volts. Next, we assemble a voltage rectifier, which can be assembled from any 4 diodes that are designed for currents of at least 250 mA and a voltage of 25 volts (but is it always better to take with a margin?). And you can buy a ready-made diode bridge on the radio market. Next, after the diode bridge, we assemble a voltage stabilizer. A voltage stabilizer is needed so that the sound in the headphones does not sag during bass, i.e. so that the voltage does not jump and at the same time the sound is not distorted. Transistors install any medium power, for example: KT805, Kt817, KT815, KT803. The transistor must be attached to the radiator. Further, capacitors C4, C5, C6 serve as a filter that removes noise. Resistors R4 and R5 play the role of limiting the current to the base of the transistor, thereby setting a certain gain. To the base of the transistor we see zener diodes. If we need a voltage of 15 volts at the output, then we set the zener diode to 15 volts, if it is 20 volts, then we set it to 20 volts, but in this case to 15 volts. We see 2 zener diodes of the D814A brand, which are connected in series and each of which is designed for a voltage of 7.5 volts (that is, in total we get 15 volts (7.5 + 7.5 = 15)). Also note that the voltage supplied to the zener diodes must exceed 1-1.5 volts for their normal operation. PSU diagram below: