There were already publications on Habré about DIY tube amplifiers, which were very interesting to read. No doubt, they sound wonderful, but for everyday use it is easier to use a transistor device. Transistors are more convenient because they do not require warming up before operation and are more durable. And not everyone dares to start a lamp saga with anode potentials under 400 V, and transistor transformers for a couple of tens of volts are much safer and simply more affordable.
I chose John Linsley Hood's 1969 circuit as the circuit to reproduce, taking the author's parameters based on the impedance of my speakers 8 ohms.
The classic circuit from a British engineer, published almost 50 years ago, is still one of the most reproducible and collects exceptionally positive reviews about itself. There are many explanations for this:
- the minimum number of elements simplifies installation. It is also believed that the simpler the design, the better the sound;
- despite the fact that there are two output transistors, they do not need to be sorted into complementary pairs;
- output of 10 watts with a margin is enough for ordinary human dwellings, and an input sensitivity of 0.5-1 volts is very well consistent with the output of most sound cards or players;
- class A - it is also class A in Africa, if we are talking about good sound. About comparison with other classes will be a little lower. 
Internal design
The amplifier starts with power. Separation of two channels for stereo is best done from two different transformers, but I limited myself to one transformer with two secondary windings. After these windings, each channel exists on its own, so we must not forget to multiply by two everything mentioned below. On the breadboard we make bridges on Schottky diodes for the rectifier.
It is possible on ordinary diodes or even ready-made bridges, but then they need to be shunted with capacitors, and the voltage drop across them is greater. After the bridges, there are CRC filters of two 33,000 microfarad capacitors and a 0.75 ohm resistor between them. If you take both the capacitance and the resistor less, then the CRC filter will become cheaper and heat up less, but the ripple will increase, which is not comme il faut. These parameters, IMHO, are reasonable in terms of price-effect. A powerful cement resistor is needed in the filter, with a quiescent current of up to 2A it will dissipate 3 W of heat, so it is better to take it with a margin of 5-10 W. For the rest of the resistors in the power circuit, 2 W will be enough.
Next, we move on to the amplifier board itself. A lot of ready-made kits are sold in online stores, but there are no less complaints about the quality of Chinese components or illiterate layouts on the boards. Therefore, it is better to do it yourself, under your own “loose”. I made both channels on a single breadboard, so that later I can attach it to the bottom of the case. Run with test items:
Everything except the output transistors Tr1/Tr2 is located on the board itself. Output transistors are mounted on radiators, more on that below. To the author's scheme from the original article, you need to make the following remarks:
Not everything needs to be soldered right away. It is better to put resistors R1, R2 and R6 first with trimmers, after all the adjustments, unsolder them, measure their resistance and solder the final fixed resistors with the same resistance. The setting is reduced to the following operations. First, using R6, it is set so that the voltage between X and zero is exactly half of the voltage + V and zero. In one of the channels, I lacked 100 kOhm, so it's better to take these trimmers with a margin. Then, with the help of R1 and R2 (keeping their approximate ratio!) the quiescent current is set - we put the tester to measure direct current and measure this very current at the input point of the plus supply. I had to significantly reduce the resistance of both resistors to get the desired quiescent current. The quiescent current of the amplifier in class A is maximum and, in fact, in the absence of an input signal, everything goes into thermal energy. For 8 ohm speakers, this current, according to the author's recommendation, should be 1.2 A at 27 volts, which means 32.4 watts of heat per channel. Since it can take several minutes for the current to be applied, the output transistors must already be on cooling heatsinks or they will quickly overheat and die. Because they get hot most of the time.
It is possible that, as an experiment, you will want to compare the sound of different transistors, so you can also leave the possibility of a convenient replacement for them. I tried on the input 2N3906, KT361 and BC557C, there was a slight difference in favor of the latter. In the pre-weekend, we tried KT630, BD139 and KT801, settled on imported ones. Although all of the above transistors are very good, and the difference can be rather subjective. At the output, I immediately put 2N3055 (ST Microelectronics), since many people like them.
When adjusting and lowering the resistance of the amplifier, the cutoff frequency of the low frequencies may increase, so for the capacitor at the input it is better to use not 0.5 microfarads, but 1 or even 2 microfarads in a polymer film. The Russian picture-scheme “Ultralinear Class A Amplifier” is still circulating on the Web, where this capacitor is generally proposed as 0.1 microfarads, which is fraught with a cutoff of all basses at 90 Hz:
They write that this circuit is not prone to self-excitation, but just in case, a Zobel circuit is placed between the X point and the ground: R 10 Ohm + C 0.1 microfarad.
- fuses, they can and should be installed both on the transformer and on the power input of the circuit.
- it would be very appropriate to use thermal paste for maximum contact between the transistor and the heatsink.
Locksmith and carpentry
Now about the traditionally most difficult part in DIY - the case. The dimensions of the case are set by radiators, and in class A they should be large, remember about 30 watts of heat on each side. At first, I underestimated this power and made a case with average radiators 800cm² per channel. However, with a set quiescent current of 1.2A, they heated up to 100 ° C in just 5 minutes, and it became clear that something more powerful was needed. That is, you need to either install larger radiators, or use coolers. I didn’t want to make a quadcopter, so I bought giant handsome HS 135-250s with an area of 2500 cm² for each transistor. As practice has shown, such a measure turned out to be a little redundant, but now the amplifier can be safely touched by hands - the temperature is only 40 ° C even in rest mode. Drilling holes in the radiators for fasteners and transistors became some problem - the originally purchased Chinese metal drills were drilled extremely slowly, it would take at least half an hour for each hole. Cobalt drills with a sharpening angle of 135 ° from a well-known German manufacturer came to the rescue - each hole is passed in a few seconds!I made the body out of Plexiglas. We immediately order cut rectangles from glaziers, make the necessary holes for fastenings in them and paint the reverse side with black paint.
The plexiglass painted on the back looks very nice. Now it remains only to assemble everything and enjoy the music ... oh yes, during the final assembly, it is also important to properly dilute the ground to minimize the background. As it was found out decades before us, C3 needs to be connected to the signal ground, i.e. to the minus of the input-input, and all other minuses can be sent to the "star" near the filter capacitors. If everything is done correctly, then no background can be heard, even if you bring your ear to the speaker at maximum volume. Another "ground" feature that is typical for sound cards that are not galvanically isolated from the computer is interference from the motherboard, which can creep through USB and RCA. Judging by the Internet, the problem is common: in the speakers you can hear the sounds of the HDD, printer, mouse and the background of the system unit's power supply. In this case, the easiest way is to break the ground loop by taping the ground on the amplifier plug with electrical tape. There is nothing to fear here, because. there will be a second ground loop through the computer.
I didn’t make a volume control on the amplifier, because I couldn’t get any high-quality ALPS, and I didn’t like the rustling of Chinese potentiometers. Instead, a conventional 47 kΩ resistor was installed between the “ground” and the “signal” of the input. Moreover, the regulator of an external sound card is always at hand, and each program also has a slider. Only the vinyl player does not have a volume control, so to listen to it, I attached an external potentiometer to the connecting cable.
I can guess this container in 5 seconds...
Finally, you can start listening. The sound source is Foobar2000 → ASIO → external Asus Xonar U7. Speakers Microlab Pro3. The main advantage of these speakers is a separate block of their own amplifier on the LM4766 chip, which can be immediately removed somewhere far away. Much more interesting with this acoustics sounded the amplifier from the Panasonic mini-system with the proud inscription Hi-Fi or the amplifier of the Soviet player Vega-109. Both of the above devices work in class AB. The JLH presented in the article outplayed all of the above comrades in one wicket, according to the results of a blind test for 3 people. Although the difference was audible to the naked ear and without any tests, the sound is clearly more detailed and transparent. It's quite easy, for example, to hear the difference between 256kbps MP3 and FLAC. I used to think that the lossless effect is more like a placebo, but now the opinion has changed. Similarly, it became much more pleasant to listen to files not compressed from loudness war - dynamic range less than 5 dB is not ice at all. The Linsley Hood is worth the time and money, as a similar branded amp will cost a lot more.Material costs
Transformer 2200 rub.Output transistors (6 pieces with a margin) 900 rubles.
Filter capacitors (4 pcs) 2700 r.
"Rose" (resistors, small capacitors and transistors, diodes) ~ 2000 rubles.
Radiators 1800 r.
Plexiglas 650 rub.
Paint 250 rub.
Connectors 600 rub.
Boards, wires, silver solder, etc. ~1000 r.
TOTAL ~12100 rub.
After mastering the basics of electronics, a novice radio amateur is ready to solder his first electronic designs. Audio power amplifiers tend to be the most repeatable designs. There are a lot of schemes, each differs in its parameters and design. This article will look at some of the simplest and most fully working amplifier circuits that can be successfully repeated by any radio amateur. The article does not use complex terms and calculations, everything is simplified as much as possible so that there are no additional questions.
Let's start with a more powerful scheme.
So, the first circuit is made on the well-known TDA2003 chip. This is a mono amplifier with an output power of up to 7 watts into a 4 ohm load. I want to say that the standard switching circuit of this microcircuit contains a small number of components, but a couple of years ago I came up with a different circuit on this microcircuit. In this scheme, the number of components is minimized, but the amplifier has not lost its sound parameters. After the development of this circuit, I began to make all my amplifiers for low-power speakers on this circuit.
The circuit of the presented amplifier has a wide range of reproducible frequencies, the supply voltage range is from 4.5 to 18 volts (typical 12-14 volts). The microcircuit is installed on a small heat sink, since the maximum power reaches up to 10 watts.
The microcircuit is capable of operating at a load of 2 ohms, which means that 2 heads with a resistance of 4 ohms can be connected to the amplifier output.
The input capacitor can be replaced with any other, with a capacitance from 0.01 to 4.7 uF (preferably from 0.1 to 0.47 uF), both film and ceramic capacitors can be used. All other components should not be replaced.
Volume control from 10 to 47 kOhm.
The output power of the microcircuit allows it to be used in low-power PC speakers. It is very convenient to use a chip for stand-alone speakers for a mobile phone, etc.
The amplifier works immediately after switching on, it does not need additional adjustment. It is advised to additionally connect the minus power supply to the heat sink. All electrolytic capacitors are preferably used at 25 volts.
The second circuit is assembled on low-power transistors, and is more suitable as a headphone amplifier.
This is probably the highest quality circuit of its kind, the sound is clear, the entire frequency spectrum is felt. With good headphones, it feels like you have a full subwoofer.
The amplifier is assembled on only 3 reverse conduction transistors, as the cheapest option, transistors of the KT315 series were used, but their choice is quite wide.
The amplifier can operate on a low-impedance load, up to 4 ohms, which makes it possible to use the circuit to amplify the signal of a player, radio receiver, etc. A 9 volt battery was used as a power source.
KT315 transistors are also used in the final stage. To increase the output power, you can use KT815 transistors, but then you will have to increase the supply voltage to 12 volts. In this case, the power of the amplifier will reach up to 1 watt. The output capacitor can have a capacitance from 220 to 2200 uF.
The transistors in this circuit do not heat up, therefore, no cooling is needed. When using more powerful output transistors, you may need small heatsinks for each transistor.
And finally - the third scheme. A no less simple, but proven version of the amplifier structure is presented. The amplifier is capable of operating from low voltage up to 5 volts, in which case the output power of the PA will be no more than 0.5 W, and the maximum power when powered by 12 volts reaches up to 2 watts.
The output stage of the amplifier is built on a domestic complementary pair. Adjust the amplifier by selecting the resistor R2. To do this, it is desirable to use a 1 kOhm trimmer. Slowly rotate the knob until the quiescent current of the output stage is 2-5 mA.
The amplifier does not have a high input sensitivity, so it is advisable to use a preamplifier before the input.
A diode plays an important role in the circuit; it is here to stabilize the output stage mode.
The output stage transistors can be replaced with any complementary pair of appropriate parameters, for example, KT816/817. The amplifier can power low-power autonomous speakers with a load resistance of 6-8 ohms.
List of radio elements
| Designation | Type | Denomination | Quantity | Note | Shop | My notepad | |
|---|---|---|---|---|---|---|---|
| Amplifier on a TDA2003 chip | |||||||
| Audio amplifier | TDA2003 | 1 | To notepad | ||||
| C1 | 47uF x 25V | 1 | To notepad | ||||
| C2 | Capacitor | 100 nF | 1 | Film | To notepad | ||
| C3 | electrolytic capacitor | 1uF x 25V | 1 | To notepad | |||
| C5 | electrolytic capacitor | 470uF x 16V | 1 | To notepad | |||
| R1 | Resistor | 100 ohm | 1 | To notepad | |||
| R2 | Variable resistor | 50 kOhm | 1 | From 10 kΩ to 50 kΩ | To notepad | ||
| Ls1 | dynamic head | 2-4 ohm | 1 | To notepad | |||
| Transistor amplifier circuit number 2 | |||||||
| VT1-VT3 | bipolar transistor | KT315A | 3 | To notepad | |||
| C1 | electrolytic capacitor | 1uF x 16V | 1 | To notepad | |||
| C2, C3 | electrolytic capacitor | 1000uF x 16V | 2 | To notepad | |||
| R1, R2 | Resistor | 100 kOhm | 2 | To notepad | |||
| R3 | Resistor | 47 kOhm | 1 | To notepad | |||
| R4 | Resistor | 1 kOhm | 1 | To notepad | |||
| R5 | Variable resistor | 50 kOhm | 1 | To notepad | |||
| R6 | Resistor | 3 kOhm | 1 | To notepad | |||
| dynamic head | 2-4 ohm | 1 | To notepad | ||||
| Transistor amplifier circuit No. 3 | |||||||
| VT2 | bipolar transistor | KT315A | 1 | To notepad | |||
| VT3 | bipolar transistor | KT361A | 1 | To notepad | |||
| VT4 | bipolar transistor | KT815A | 1 | To notepad | |||
| VT5 | bipolar transistor | KT816A | 1 | To notepad | |||
| VD1 | Diode | D18 | 1 | Or any low power | To notepad | ||
| C1, C2, C5 | electrolytic capacitor | 10uF x 16V | 3 | ||||
Circuit diagram of a simple transistor audio amplifier, which is implemented on two powerful composite transistors TIP142-TIP147 installed in the output stage, two low-power BC556B in the differential path and one BD241C in the signal pre-amplification circuit - only five transistors for the entire circuit! Such a UMZCH design can be freely used, for example, as part of a home music center or to drive a subwoofer installed in a car, at a disco.
The main attraction of this sound power amplifier lies in the ease of assembly even by novice radio amateurs, there is no need for any special settings, there are no problems in purchasing components at an affordable price. The PA circuit presented here has electrical characteristics with high linearity of operation in the frequency range from 20Hz to 20000Hz. p>
When choosing or self-manufacturing a transformer for a power supply, the following factor must be taken into account: - the transformer must have a sufficient power margin, for example: 300 W per one channel, in the case of a two-channel version, then naturally the power doubles. You can use your own separate transformer for each, and if you use the stereo version of the amplifier, then you will generally get a “double mono” type device, which will naturally increase the efficiency of sound amplification.
The operating voltage in the secondary windings of the transformer should be ~ 34v alternating, then the constant voltage after the rectifier will be in the region of 48v - 50v. In each power supply arm, it is necessary to install a fuse rated for a working current of 6A, respectively, for a stereo when working on one power supply - 12A.
I want to present the design of a simple but powerful low-frequency amplifier, made on modern inexpensive transistors. The main advantages of this amplifier are ease of assembly, affordable and cheap radio components, and the finished amplifier does not need to be adjusted and works immediately. The amplifier develops very high power compared to similar circuits. Of the electrical parameters, I would like to note a very high linearity in the operating frequency range from 20Hz to 20kHz. True, it was not without drawbacks either. This circuit has an increased noise level at high volume, but given the simplicity and affordability, it’s still worth assembling an amplifier, I especially advise motorists for a powerful subwoofer, since the power of such a circuit makes it possible to swing high-power imported heads. From the diagram it is clear that nowhere is easier. The circuit uses only 5 transistors and several additional radio components.
To reduce the noise level of the amplifier, you will need to put a variable resistor at the input, with a resistance of 20 to 100 kOhm, they also adjust the volume. In this case, at a low volume, there will be practically no noise, and at a high volume, the noise is almost inaudible, and if the amplifier works with a low-pass filter at the input (under the subwoofer), then there will be no noise at all.
The amplifier is capable of delivering about 100 watts into an 8 ohm load! if a head with a resistance of 4 ohms is used, then the power increases to 150 watts! UMZCH parameters:
Voltage Gain .............................................................................. ........20
Supply voltage Up.................................................... ................................+-15…+-50V
Rated power P at Upit = +-30V at 4 Ohm .............................................. ....100W
Maximum power Pmax Upit=+-45V at 4Ω.................................................. ..150W
Sensitivity at the input Uin.................................................... .........................1V
The total coefficient of all types of distortion at P=60W 4Ohm, Kd.........................0.005%
Amplifier quiescent current Ixx.............................................. ....................................20-25mA
Output stage quiescent current ............................................................... ...............................0mA
Bandwidth of reproducible frequencies by level -3 dB, Hz, .............................. 5-100 000
The parameters are good enough, the only obstacle to using the circuit as a car amplifier is an increased bipolar power supply, but this is not such a big hindrance, since a lot of voltage converter circuits are known today, one of such circuits is performed on the TL494 chip. The circuit is standard and allows you to get up to 200 watts of power at the output of the transformer, which is quite enough for the full operation of this home-made amplifier. I don’t cite the converter circuit, since this is a completely different topic.
Evgenia Smirnova
To send light into the depths of the human heart - this is the purpose of the artist
Content
Connecting speakers to a laptop, TV, or other music source sometimes requires amplifying the signal with a separate device. The idea of building an amplifier is a good one if you are prone to PCB work at home and have some technical skills.
How to make a sound amplifier
Getting started on assembling an amplifying device for speakers of one type or another consists of finding tools and components. The amplifier circuit on a printed circuit board is assembled using a soldering iron on a heat-resistant support. It is recommended to use special soldering stations. If DIY assembly is for circuit testing purposes or for short term use, the on-wire option will do, but you will need more space to accommodate the components. The printed circuit board guarantees compactness of the device and convenience in further use.
A cheap and common amplifier for headphones or small speakers is created on the basis of a microcircuit - a miniature control unit with a pre-wired set of commands for controlling an electrical signal. It remains to add only a few resistors and capacitors to the circuit with a microcircuit. The total cost of an amateur-class amplifier is, as a result, much lower than the price of finished professional equipment from the nearest store, but the functionality is also limited to changing the output volume of the audio signal.
Remember the features of compact single-channel amplifiers assembled by yourself based on TDA series microcircuits and their analogues. The chip generates a lot of heat during operation, so you should avoid or minimize its contact with other parts of the device. Radiator grill for heat dissipation is recommended for use. Depending on the model of the microcircuit and the power of the amplifier, the size of the required radiator increases. If the amplifier is assembled in a case, you should first plan a place for a heat sink.
Another feature of assembling a sound amplifier with your own hands is the low voltage consumption. This allows you to use a simple amplifier in cars (powered by a car battery), on the road or at home (powered by a special unit or batteries). Some simplified audio amplifiers require only 3 volts of current. The power consumption depends on how much amplification of the audio signal is required. The sound amplifier from the player for standard headphones consumes about 3 watts.
A novice radio amateur is recommended to use a computer program to create and view circuit diagrams. Files for such programs may have the extension *.lay - they are created and edited in the popular virtual tool Sprint Layout. Creating a DIY circuit from scratch makes sense if you have already gained experience and want to experiment with the knowledge gained. Otherwise, look for and download ready-made files, according to which you can quickly assemble a replacement for a low-frequency amplifier for a car radio or a digital combo amplifier for a guitar.
For laptop
A do-it-yourself sound amplifier is being assembled for a laptop in one of two cases: the built-in speakers are out of order, or their volume and sound quality are not enough for your needs. You will need a simple amplifier, designed for external speakers up to 2 watts, and winding resistance up to 4 ohms. To assemble it with your own hands, in addition to standard radio amateur tools (pliers, a soldering station), you will need a printed circuit board, a TDA 7231 chip, and a 9-volt power supply. Choose your own cabinet to house the components of the amplifier.
Add the following items to the list of purchased components:
- non-polar capacitor 0.1 uF - 2 pcs.;
- polar capacitor 100 uF - 1 pc.;
- polar capacitor 220 uF - 1 pc.;
- polar capacitor 470 uF - 1 pc.;
- constant resistor 10 KΩ - 1 pc.;
- resistor constant 4.7 Ohm - 1 pc.;
- two-position switch - 1 pc.;
- speaker output jack – 1 pc.
Determine the assembly order yourself, depending on which *.lay format wiring diagram you downloaded. Choose a radiator of such a size that its thermal conductivity allows you to keep the operating temperature of the microcircuit below 50 degrees Celsius. If the device is constantly used with a laptop outdoors, it will require a homemade case with slots or holes for air circulation. You can assemble such a case with your own hands from a plastic container or the remnants of old radio equipment, fixing the board with long screws.
For DIY headphones
The simplest stereo amplifier for portable headphones should have little power, but the most important parameter will be power consumption. In an ideal example, the design is powered by AA batteries, in extreme cases, from a simple 3 Volt adapter. You will need a high-quality TDA 2822 chip or its equivalent (for example, KA 2209), an electronic circuit for assembling an amplifier with your own hands on a TDA 2822. Additionally, take the following components:
- capacitors 100 uF (4 pcs.);
- up to 30 cm of copper wire;
- headphone jack.
A heat sink element is needed if you want to make the amplifier compact and with a closed case. You can assemble the amplifier on a finished or home-made printed circuit board or by surface mounting. The pulse transformer in the power supply can create noise, so do not use it in this variant of the amplifier. The ready amplifier will provide a pleasant and powerful sound from the player (records or radio signal), tablet or phone.
Subwoofer amplifier circuit
The low-frequency amplifier is assembled by hand on the TDA 7294 chip. It is used both to create powerful acoustics with bass in the apartment, and as an auto amplifier - in this case, however, you need to purchase a bipolar 30-35 Volt power supply. The figures below describe the location of components, as well as the rating of resistors and capacitors. This subwoofer amplifier will provide up to 100 watts of output power with prominent low frequencies.
Mini speaker amplifier
As a sound amplification device for domestic or foreign home speakers, the design described above for laptops is suitable. Stationary placement of the device will allow you to choose any power adapter available. You can ensure the miniature and acceptable appearance of an inexpensive amplifier by observing a few rules:
- Ready-made high-quality printed circuit board.
- Durable plastic or metal case (order from the master).
- The placement of components is pre-planned.
- The amplifier is soldered neatly, without extra drops of solder.
- The heatsink only touches the chip.
- Ready-made sockets for signal output and power input are used.
DIY tube sound amplifier
Tube audio amplifiers are expensive devices, provided that you purchase all the components with your own funds. Older radio amateurs sometimes keep collections of lamps and other parts. Assembling a tube amplifier at home is relatively easy if you are willing to spend a few days searching the internet for detailed schematics. The sound amplifier circuit in each case is unique and depends on the sound source (old tape recorder, modern digital technology), power source, estimated dimensions and other parameters.
Transistor audio amplifier
Assembling a sound preamplifier with your own hands without the use of complex microcircuits is possible on transistors. The amplifier on germanium transistors is easily built into modern audio systems, it does not require additional configuration. The disadvantage of transistor circuits is the larger size of the assembled boards. Dependence on the "purity" of the background is also unpleasant - you will need a shielded cable, or an additional noise and ripple suppression circuit from the network.