Amplifier circuits for computer speakers. Radio circuits electrical circuit diagrams

For computer user A laptop is undoubtedly a convenient, compact and quite functional device. But, unfortunately, this device is not without flaws.

Surely, many users of laptops and netbooks have encountered the problem of quiet sound reproduction through the built-in speakers of these devices.

If at home you can connect an external stereo system, then outside the home walls it is impossible and you have to limit yourself to headphones. In this case, there is no talk of collective viewing of any film or series.

How to fix the situation?

To correct the current situation, portable computer speakers powered by a USB port will help. Now on the shelves of stores there is a huge selection of these devices, but their quality can vary significantly.

The price of portable computer speakers powered by a USB port is quite low and affordable for a wide segment of the population. Despite this, the purchase of this device may be unsuccessful, since the quality of sound reproduction by such a system leaves much to be desired. Oddly enough, but among the cheap devices of this class there are devices of very good quality, both in design and in sound reproduction quality.

We will “open” a portable speaker system powered by a USB port and study the electronic filling of this device. From the point of view of a radio amateur, it is curious to know what electronic components such devices are assembled from. The knowledge gained can come in handy when building USB-powered portable speakers or repairing them yourself.

We will disassemble portable multimedia USB speakers of the brand Sven 315. Despite their cheapness, this model of portable speakers showed good quality reproduction and sound power sufficient for scoring a small room.

Disassembly of computer USB speakers

Portable speakers are easy to disassemble. To open the case, carefully remove the front decorative panel.

In order to get printed circuit board amplifier, you need to unscrew the fixing nut, which is hidden under the plastic knob of the volume control. After that, the electronic board can be freely removed from the housing.

Electronic stuffing

The composition of the electronic filling of the device turned out to be quite simple. On a small printed circuit board, an integrated circuit of a stereo amplifier based on a microcircuit is mounted. LM4863D. With a supply voltage of 5 volts, this microcircuit can produce 2.2 watts of output power per channel with a speaker voice coil resistance of 4 ohms. Based on the description (datasheet) THD + noise ( THD+N) at maximum output power is 1%.

Amplifier board and speaker

Based on these data, we can conclude that based on the LM4863D chip, you can assemble a pretty good stereo amplifier with low-voltage power supply (5V) and an output power of 2 W per channel. Many who are not yet familiar with modern microcircuits believe that TDA2822 is suitable instead of LM4863D. It's a delusion! TDA2822 is very gluttonous (compared to LM4863) and produces strong signal distortion at maximum power. Also, the optimal power supply for the TDA2822 is about 12 volts, which is not good for portable equipment. The TDA2822 can be recommended as a readily available replacement if the LM4863 is not available. This can happen, for example, during repairs.

It is worth noting that the LM4863 chip was developed specifically for compact systems, so the chip requires a minimum of external elements (the so-called strapping). The microcircuit is available in different packages, from the usual DIP to the compact SOIC.

If there is a desire to independently assemble an amplifier based on the LM4863 chip, then you may encounter a problem. Finding this chip on the radio markets is not so easy (as it was at the time of this writing). But it was not difficult to find such a microcircuit on online trading platforms. For example, in the AliExpress.com online store, the LM4863 chip is easy to find in various cases and in any quantity. The price of 1 microcircuit is less than $1, if you buy 10 pieces at once.

How to buy radio components on Aliexpress, I told.

In addition to the amplifier chip itself, the printed circuit board has a connector for connecting a passive speaker (without a built-in amplifier), a dual variable resistor for adjusting the input audio signal and an electrolytic capacitor. On the side of the printed conductors of the circuit board, SMD strapping elements are installed, which are necessary for the operation of the integrated amplifier. The microcircuit is powered from the USB connector, which is connected to any free port of a laptop or desktop computer.

A typical connection diagram for the LM4863 chip is taken from the description (datasheet "a) for this chip and is shown in the figure.

Typical circuit for switching on the LM4863 chip (taken from the description)

According to the typical circuit for switching on the LM4863 chip, it can be seen that it can also work on ordinary headphones ( headphone), the resistance of which is 32 ohms. The microcircuit provides a circuit for determining the connection of headphones, and pin 16 (HP-IN) is assigned to implement this function.

For those who understand electronics and datasheets on English language they are not afraid, LM4863 chips can easily be found on the Internet at alldatasheet.com.

Portable USB speaker amplifier circuit

The circuit diagram of the amplifier was manually reduced from the printed circuit board of computer USB speakers Sven-315. The diagram shows one capacitor C2 instead of two (C7,C9) that are actually present on the PCB (see below). This is because on the PCB the capacitors are connected in parallel (C7 and C9), and in the reduced circuit, the capacitor C2 indicates the total capacitance of these two capacitors.

Schematic diagram of an amplifier based on the LM4863D (hand-mixed)

As you can see, the typical circuit from the description differs from the one that was manually reduced from the printed circuit board of the computer speaker amplifier. There are no elements on the diagram that are installed if a headphone jack is added to the circuit. Otherwise, the circuit corresponds to the typical one given in the description for the LM4863 chip.

Placement of elements on the printed circuit board

If you plan to use portable speakers without a laptop, for example, in conjunction with an MP3 player, then a 5-volt power adapter is quite suitable to power the speakers. The main thing is that the power adapter can provide sufficient load current (as a rough estimate: the standard load current for USB ports is no more than 500 mA). According to the description for the LM4863 chip, the maximum quiescent current (when no sound signal is applied to the chip) is 20 mA. Naturally, during playback, the current consumption will be higher.

The photo shows the option of powering SVEN-315 portable speakers from a 5-volt adapter, which is used to charge the iPod player. The maximum load current of the adapter is 1A, which is more than enough for the regular operation of portable speakers.

As it turned out, high-quality sound reproduction of SVEN-315 portable speakers lies in the rational design of the case. As you know, the quality of sound acoustic systems is affected not only by the loudspeakers used in them, but also by the case. To verify this, just pull the speaker out of the case and turn on playback. The quality and sound power of playback will be much worse. This remark was not made by chance, since we compared the sound reproduction quality of SVEN-315 portable speakers and similar, but more expensive SVEN PS-30 USB speakers.

Despite the fact that SVEN PS-30 sound speakers are mounted on the basis of the CM6120-S integrated USB audio chip, which includes a 16-bit DAC and class D sound amplifiers, the quality of their sound reproduction is subjectively (aurally) much worse due to poor performance of the acoustic system enclosure.

The housing of SVEN-315 portable speakers is made of ABS plastic. Perhaps it is the design of the case that allows you to “squeeze out” all their modest capabilities from small-sized speakers.

My kids love to drive a computer .. And then one fine day the computer speakers blazed with a blue flame, in connection with which my headphones began to disappear from time to time. And since I have two children, I practically did not see my headphones. It couldn’t go on like this for a long time, and then he told them: “I’ll think of something with the speakers.”

Tools used: soldering iron, pliers, side cutters, screwdriver, 8mm drill, stranded wires, solder, screw contacts, amplifier board.

It was decided not to buy new ones, but to adapt unused rear speakers from a 5.1 receiver. But they need an amplifier. There is no finished amplifier. I dug out in the bins a board with a class D amplifier bought for a long time on Aliexpress - I lay for a long time, waiting in the wings.

This is a digital amplifier based on the TA2024 chip from the Korean manufacturer Tripath, a high-quality power amplifier with low non-linear distortion and high efficiency.

Amplifier characteristics specified by the manufacturer:
- class D amplifier;
- supply voltage 9-14V;
- high sensitivity;
coefficient of non-linear distortion:
- 0.1%, 9W, 4Ω;
- 0.1%, 6W, 8Ω;
- 10%, 15W, 4Ω;
- 10%, 10W, 8Ω;
- Efficiency 84%, 15W, 4 Ohm;
- Efficiency 90%, 10W, 8 Ohm;
- overvoltage protection;
- overload protection;
- protection against excess temperature.
Dimensions: 90x53 mm.

Step 1.
Placement of the amplifier board in the computer case
At first, a separate case with a power supply was supposed, but in the process he abandoned this idea and decided to place the amplifier directly in the computer. We will take power from the computer's power supply, since there is +12 v. Now the question is: where and how to fix the amplifier board in the computer case. In my case, I decided to fix the amplifier at the bottom of the case, closer to the source of the sound signal. Racks made of screws with tubes on. I refused to drill the case due to the formation of metal chips during drilling, which can close something. I glued the racks to the body with hot glue.

They also grabbed the amplifier itself to the racks.

Step 2
We make contacts for connecting speakers
To connect the speakers, I found screw contacts from some old device. I placed them on the cover for the PCI slot of the computer. To do this, I marked and drilled four holes with a diameter of 8 mm in the plug. Screwed contacts. I put it in place and fixed the plug.

It remains to make all the connections.

Step 3
Electrical connections
There was a problem where to get the sound signal. In the manual of the motherboard subtracted where it has a sound output.

To connect to the amplifier, I slightly altered the audio cable from the cd-rom drive. I got it like this. On other motherboards, the connection may differ, you need to look at the place.

The amplifier is sensitive, when connected directly at the minimum volume, noise from a running computer is heard. Since the amp does not have an input level control, you need to put a variable resistor on the input. Instead, I soldered the voltage divider as in the diagram.

Here's what happened.

With these parameters, the maximum volume suited me (well, so that the neighbors would not hang themselves), noise from interference is not audible.
To connect to the power supply, I cut off the connector from the old MOLEX computer fan.

All stripped sections of wires were tinned with solder. I soldered pieces of wire to the screw contacts, tried them on in place, off with the excess, cleaned the ends, tinned them. All wiring was clamped with screws on the amplifier terminal block.

This audio amplifier circuit was created by everyone's favorite British engineer (electronics engineer) Linsley-Hood. The amplifier itself is assembled on only 4 transistors. It looks like an ordinary bass amplifier circuit, but this is only at first glance. An experienced radio amateur will immediately understand that the output stage of the amplifier works in class A. It is ingenious that it is simple and this circuit is proof of that. This is a super-linear circuit where the shape of the output signal does not change, that is, at the output we get the same waveform as at the input, but already amplified. The scheme is better known as JLH - class A ultra-linear amplifier, and today I decided to present it to you, although the scheme is far from new. Any ordinary radio amateur can assemble this sound amplifier with his own hands, due to the absence of microcircuits in the design, which makes it more affordable.

How to make a speaker amplifier

Sound amplifier circuit

In my case, only domestic transistors were used, since it was not easy to find with imported ones, and even standard circuit transistors. The output stage is built on powerful domestic transistors of the KT803 series - it is with them that the sound seems better. To build up the output stage, a medium-power transistor of the KT801 series was used (it was difficult to find). All transistors can be replaced with others (KT805 or 819 can be used in the output stage). Changes are not critical.

Advice: who decides to taste this homemade sound amplifier - use germanium transistors, they sound better (IMHO). Several versions of this amp have been made, they all sound… divine, I can't find any other words.

The power of the presented circuit is not more than 15 watts(plus minus), current consumption 2 Amperes (sometimes a little more). The output stage transistors will get warm even without a signal being applied to the input of the amplifier. Strange phenomenon, isn't it? But for class amplifiers. And, this is quite normal, a large quiescent current - business card literally all known schemes of this class.

The video shows the operation of the amplifier itself, connected to the speakers. Please note that the video was filmed on a mobile phone, but the sound quality can be judged in this way. To test any amplifier, you just need to listen to just one melody - Beethoven's "Fur Elise". After turning it on, it becomes clear what kind of amplifier is in front of you.

90% of microcircuit amplifiers will not pass the test, the sound will be “broken off”, wheezing and distortion can be observed at high frequencies. But the above does not apply to John Linsley's circuit, the ultra-linearity of the circuit allows you to completely repeat the shape of the input signal, thus obtaining only pure gain and a sinusoid at the output.

A friend from a neighboring department where they design various electronic devices asked me to create a simple two-channel amplifier for a computer. Due to poor funding and the greediness of the head of the department, they did not allocate money for the purchase of normal computer speakers for the PC (there is nothing to be distracted from work). Therefore, we set a goal - to assemble ULF with zero costs. The idea of ​​an amplifier built into a PC system unit has long been discussed on our forum, so armed with an UMZCH unit on a TDA2005, broken off from an old (even ancient) car radio and an unnecessary floppy, I started assembling it.

As you may have guessed, a floppy drive will be used as a housing for the ULF. It is unlikely that anyone needs it now, and everyone has a bunch of non-working ones. Moreover, the dimensions are optimal, and there is a + 12V power socket on the back, which we connect to the cable from the ATX power supply.

We disassemble the case and pull out everything unnecessary, freeing up space for the amplifier board.

Perhaps some of this will later come in handy in other designs, so do not rush to immediately throw it away.

The front panel is not very well suited for installing volume controls and jacks, so we cover it with an aluminum overlay cut from a piece of 1.5 mm thick plate.

It was possible to simplify the design and abandon the RG, but then when the PC is turned on and off, the speakers will yell at full power - not buzzing. In view of the maximum cost reduction, I did not install a dual volume control, but put a single resistor per channel - I have 100 of them, unlike stereo.

We solder all the necessary connecting wires to the printed circuit board, according to the standard ULF scheme on TDA2005.

If this microcircuit is not available, put any other one designed for power supply from 12V. For example TDA2003, TDA1552, TDA1555, TDA8560 and some others.

External speakers are connected via a regular audio jack, like from headphones. The same is at the line output of the system unit. Looking at the next photo you ask: Why are the regulator caps square? And this is to make it more beautiful :)

After placing the amplifier board in the floppy case (do not forget to provide for cooling - a thick aluminum plate or the drive case itself), we conduct a test. Just in no case immediately apply voltage to the ULF from the computer! First, power it from a small power supply or from batteries, and after making sure that it works normally, connect it to the ATX PSU cable.

We insert the finished amplifier into the proper place for FDD and by connecting the pegs we turn on the power. In the photo it is still before installation - it is being tested.

The sound turned out so loud that now you can arrange a disco in the department, so long as the director does not hear :)

Discuss the article AMPLIFIER BUILT IN A COMPUTER

Using a desktop computer without sound is very problematic. You can't listen to music or watch a movie. Unless in headphones, because. An audio amplifier for connecting external acoustics is not provided in the computer. Of course, stores in our technological age offer a variety of models of various price categories, but you can try to provide yourself with a good sound environment on your own.

Sound amplifier for computer

Consider one of the simplest amplifiers. Collecting which, perhaps, will be possible for anyone who knows how to hold a soldering iron in their hands and understands at least a little the basics of physics.
The basis of the amplifier will be the TDA 1557 chip, which is widely distributed in radio stores,

Chip TDA 1557Q for computer audio amplifier

which is a bridge stereo amplifier with a simple connection diagram, which can be assembled and surface-mounted by soldering the parts directly on the legs of the microcircuit without etching the printed circuit board.

To assemble the amplifier, in addition to the microcircuit itself, you will need: 2 resistors with a resistance of 10 kOhm, 3 film capacitors, 2 of which are 0.22 - 0.47 uF (220n -470n) and one 0.1 uF (100n), an electrolytic capacitor with a capacity of 2.200 - 10.000 uF with an operating voltage of at least 16 V and a button or toggle switch to turn the amplifier on and off. The cost of all parts for assembly varies from $ 10 to $ 15 or 400 - 600 rubles. You will also need some shielded wire and speakers or speakers with a power of 15 - 30 watts, a resistance of 4 - 8 ohms. A visual installation diagram is shown below.

Amplifier connection diagram on TDA1557Q

Sound must be supplied to the amplifier from the headphone output of the computer sound card with a shielded wire to avoid background and extraneous noise from the speakers. electrolytic capacitor solder with the shortest possible wires. The level of voltage drop at power peaks depends on the size of its capacitance, hence the depth and purity of the bass. It is recommended to set at least 2.200 uF. There is no upper capacity limit.
Directly to the legs of this capacitor, you can solder a film 0.1 microfarad. The toggle switch is used to smoothly turn on the amplifier so that there is no click in the speakers when power is applied and the volume is muted, the amplifier sleeps.
The amplifier operates at a voltage of 10 - 18 V, therefore, you can connect it from the computer's power supply from the + 12V output and the COM ground.