Using a high-quality amplifier will increase the detail and realism of your favorite music reproductions.
DIY amplifier 100W/200W
A 47 kOhm variable resistor is placed at the input of the first transistor, which also reduces the noise level of the amplifier.
At minimum volume the noise is not audible, but at maximum it is masked by the useful signal.
Product parameters: 150W per 4 Ohm load and 100W per 8 Ohm load.
The second one does not have the disadvantages of the first one regarding noise. The amplifier operates in class B, diodes D2-D3-D4 set this operating mode for the output transistors VT4-VT5.
Transistors VT3-VT5 are installed on the heat sink, using thermal paste through insulating gaskets.
A self-made ULF can be used in an active speaker; the low-frequency reproduction in a subwoofer is excellent.
In this article on our website www.site we will tell you how to assemble it yourself, which will allow you to save on purchasing ready-made models.
Which power amplifier will be the best?
There is no consensus on which type of amplifier is the best. Currently, it is possible to independently assemble two types of sound amplifiers:
Tube models were popular in the recent past. They are larger in size and have higher power consumption. But at the same time, these are superior to their competitors in sound quality.
Transistor amplifiers have a compact size and low power consumption. At the same time, they provide excellent sound quality.
Where to start?
First, you need to decide on the power of the future amplifier. The standard power setting for using an amplifier at home is a level of 30 - 50 W. If you need to make one that will be used for large-scale events, the power can be 200-300 watts.
To work we will need the following tools:
- Screwdriver Set.
- Multimeter.
- Soldering iron.
- Material for making the case.
- Electrical parts.
- Textolite for printed circuit board.
In essence, printed circuit boards are the basis for the future amplifier. Assembling it at home will not be difficult.
To make your own printed circuit board you will need:
- Textolite with copper foil.
- Detergent.
- Household iron.
- Self-adhesive Chinese film.
- Laser printer.
- Drill for working with the board.
A piece of cotton cloth or gauze swab. We cut out the blank for the future board from the PCB. Leave a centimeter margin on each side. Using a detergent, it is necessary to treat a piece of PCB so that the copper foil turns pink. We wash the workpiece we made and listen to it carefully.
Glue the self-adhesive film to an A4 sheet. We print out the blank of the future board on the printer. It is recommended to set the printer toner supply to maximum. Place plywood, an old book and the board on top with the foil facing up on the work surface. We cover everything with office paper and warm it thoroughly with a hot iron. It takes about 1 minute to warm up.
We apply the printed circuit from a sheet of paper to the heated board. Cover the board with a sheet of paper on top and heat it with an iron for 30 seconds. Smoothes the pattern using a tampon with transverse and longitudinal movements. Wait for the workpiece to cool, after which you can remove the backing from it.
How to etch a board correctly?
For manufacturing, it is necessary to apply all used tracks for radio components to the board. You can do this work using a CD marker, and then etch the board with ferric chloride. Unfortunately, ferric chloride is expensive, so many people replace it with a self-prepared solution of table salt and copper sulfate.
Proportions of the prepared mixture:
- Kitchen salt – 200 grams.
- Copper sulfate – 100 grams.
- 1 liter of warm water.
After mixing all the components, place the degreased and clean nails or metal products into the container.
The Metalist company specializes in the manufacture of various types of metal structures. The company's clients are offered both standard metal structures and the possibility of producing them according to individual orders. Custom parts and metal products are offered at affordable prices, and their production is carried out in the shortest possible time.
Assembling the amplifier
At the initial stage, the used radio components are installed on the printed circuit board. Consider the polarity and power of all components used. Carry out this work in full accordance with the existing circuit, which will avoid the risk of a short circuit. Having completed assembling the board, you can proceed to manufacturing the case.
The dimensions of the future amplifier depend on the dimensions of the board and the power supply used. You can also use ready-made factory cabinets from old amplifiers. We can recommend that you make the case manually from chipboard. Subsequently, you can easily finish the manufactured body with veneer or self-adhesive film.
Before final assembly, it is necessary to test run the amplifier. The power supply, board and all used components are installed. At this point, the work of making an amplifier with your own hands is completely completed, and you can enjoy high-quality sound.
The power source must provide a stable or unstable bipolar supply voltage of ±45V and a current of 5A. This ULF transistor circuit is very simple, since the output stage uses a pair of powerful complementary Darlington transistors. In accordance with the reference characteristics, these transistors can switch current up to 5A at an emitter-collector junction voltage of up to 100V.
The ULF circuit is shown in the figure below.
The signal requiring amplification through the preliminary ULF is fed to a preliminary differential amplifier stage built on composite transistors VT1 and VT2. The use of a differential circuit in the amplifier stage reduces noise effects and ensures negative feedback. The OS voltage is supplied to the base of transistor VT2 from the output of the power amplifier. DC feedback is implemented through resistor R6. The feedback on the variable component is carried out through resistor R6, but its value depends on the ratings of the chain R7-C3. But it should be borne in mind that too much increase in resistance R7 leads to excitation.
The DC operating mode is ensured by selecting resistor R6. The output stage based on Darlington transistors VT3 and VT4 operates in class AB. Diodes VD1 and VD2 are needed to stabilize the operating point of the output stage.
Transistor VT5 is designed to drive the output stage; its base receives a signal from the output of the differential pre-amplifier, as well as a constant bias voltage, which determines the DC operating mode of the output stage.
All circuit capacitors must be designed for a maximum DC voltage of at least 100V. It is recommended to mount the output stage transistors on radiators with an area of at least 200 cm square
The considered circuit of a simple two-stage amplifier is designed for use with headphones or for use in simple devices with a pre-amplifier function.
The first transistor of the amplifier is connected according to a common emitter circuit, and the second transistor is connected to a common collector. The first stage is intended for basic signal amplification in terms of voltage, and the second stage amplifies the signal in terms of power.
The low output impedance of the second stage of a two-stage amplifier, called an emitter follower, allows you to connect not only high-impedance headphones, but also other types of acoustic signal converters.
This is also a two-stage ULF circuit made on two transistors, but of opposite conductivity. Its main feature is that the connection between the cascades is direct. The covered OOS through resistance R3 bias voltage from the second stage passes to the base of the first transistor.
Capacitor SZ, bypasses resistor R4, reduces the negative feedback on alternating current, thereby reducing the gain of VT2. By selecting the value of resistor R3, the operating mode of the transistors is set.
UMZCH on two transistors |
This fairly lightweight audio power amplifier (UMPA) can be soldered using just two transistors. With a supply voltage of 42V DC, the amplifier output power reaches 0.25 W into a 4 ohm load. Current consumption is only 23 mA. The amplifier operates in single-cycle “A” mode.
Low frequency voltage from the signal source approaches the volume control R1. Next, through the protective resistor R3 and capacitor C1, the signal appears at the base of the bipolar transistor VT1 connected according to a circuit with a common emitter. The amplified signal through R8 is fed to the gate of a powerful field-effect transistor VT2, connected according to a circuit with a common source and its load is the primary winding of a step-down transformer. A dynamic head or speaker system can be connected to the secondary winding of the transformer.
In both transistor stages there is local negative feedback on direct and alternating current, as well as by a common OOS circuit.
If the gate voltage of a field-effect transistor increases, the drain-source resistance of its channel decreases and the voltage at its drain decreases. This also affects the signal level entering the bipolar transistor, which reduces the gate-source voltage.
Together with local negative feedback circuits, the operating modes of both transistors are thus stabilized even in the event of a slight change in the supply voltage. The gain depends on the ratio of the resistances of resistors R10 and R7. Zener diode VD1 is designed to prevent failure of the field-effect transistor. The amplifier stage at VT1 is powered through the RC filter R12C4. Capacitor C5 is blocking in the power supply circuit.
The amplifier can be assembled on a printed circuit board measuring 80x50 mm, on which all the elements are located except the step-down transformer and the dynamic head
The amplifier circuit is adjusted at the supply voltage at which it will operate. For fine tuning, it is recommended to use an oscilloscope, the probe of which is connected to the drain terminal of the field-effect transistor. By applying a sinusoidal signal with a frequency of 100 ... 4000 Hz to the amplifier input, by adjusting the tuning resistor R5, we ensure that there is no noticeable distortion of the sinusoid with the signal amplitude swing at the transistor drain terminal being as large as possible.
The output power of the field-effect transistor amplifier is small, only 0.25 W, the supply voltage is from 42V to 60V. Dynamic head resistance is 4 Ohms.
The audio signal through variable resistance R1, then R3 and separating capacitance C1 is supplied to the amplifier stage on a bipolar transistor according to a common emitter circuit. Next, from this transistor the amplified signal passes through resistance R10 to the field-effect transistor.
The primary winding of the transformer is a load for the field-effect transistor, and a four-ohm dynamic head is connected to the secondary winding. By the ratio of resistances R10 and R7 we set the degree of voltage amplification. In order to protect the unipolar transistor, a zener diode VD1 was added to the circuit.
All part values are shown in the diagram. The transformer can be used like TVK110LM or TVK110L2, from the frame scanning unit of an old TV or similar.
UMZCH according to Ageev’s scheme |
I came across this circuit in an old issue of a radio magazine, the impressions from it were most pleasant, firstly, the circuit is so simple that even a novice radio amateur can assemble it, and secondly, provided that the components are working and the assembly is correct, it does not require adjustment.
If you are interested in this circuit, then you can find the rest of the details on its assembly in Radio Magazine No. 8 for 1982.
High quality transistor ULF |
There was a desire to assemble a more powerful Class A amplifier. After reading a sufficient amount of relevant literature, I chose the latest version from what was offered. It was a 30 W amplifier corresponding in its parameters to high-class amplifiers.
I did not intend to make any changes to the existing routing of the original printed circuit boards, however, due to the lack of original power transistors, a more reliable output stage was chosen using 2SA1943 and 2SC5200 transistors. The use of these transistors ultimately made it possible to provide greater output power to the amplifier. The schematic diagram of my version of the amplifier is below.
This is an image of boards assembled according to this circuit with Toshiba 2SA1943 and 2SC5200 transistors.
If you look closely, you can see on the printed circuit board along with all the components there are bias resistors, they are 1 W carbon type. It turned out that they are more thermostable. When any high-power amplifier operates, a huge amount of heat is generated, so maintaining a constant rating of the electronic component when heating it is an important condition for the high-quality operation of the device.
The assembled version of the amplifier operates at a current of about 1.6 A and a voltage of 35 V. As a result, 60 W of continuous power is dissipated on the transistors in the output stage. I should note that this is only a third of the power they can handle. Try to imagine how much heat is generated on the radiators when they are heated to 40 degrees.
The amplifier case is made by hand from aluminum. Top plate and mounting plate 3mm thick. The radiator consists of two parts, its overall dimensions are 420 x 180 x 35 mm. Fasteners - screws, mostly with a countersunk stainless steel head and M5 or M3 thread. The number of capacitors was increased to six, their total capacity is 220,000 µF. A 500 W toroidal transformer was used for power supply.
Amplifier power supply
The amplifier device, which has copper busbars of the appropriate design, is clearly visible. A small toroid is added for controlled flow under the control of a DC protection circuit. There is also a high-pass filter in the power supply circuit. For all its simplicity, it must be said deceptive simplicity, the board topology of this amplifier produces sound as if without any effort, implying in turn the possibility of its infinite amplification.
Oscillograms of amplifier operation
3 dB roll-off at 208 kHz
Sine wave 10 Hz and 100 Hz
Sine wave 1 kHz and 10 kHz
100 kHz and 1 MHz signals
Square wave 10 Hz and 100 Hz
Square wave 1 kHz and 10 kHz
60 W total power, 1 kHz symmetry cutoff
Thus, it becomes clear that a simple and high-quality design of an UMZCH is not necessarily made using integrated circuits - only 8 transistors allow you to achieve decent sound with a circuit that can be assembled in half a day.
After mastering the basics of electronics, the novice radio amateur is ready to solder his first electronic designs. Audio power amplifiers are typically the most repeatable designs. There are quite a lot of schemes, each with its own parameters and design. This article will discuss several simple and 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 no additional questions arise.
Let's start with a more powerful circuit.
So, the first circuit is made on the well-known TDA2003 microcircuit. 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 circuit for connecting 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 circuit, the number of components is reduced to a minimum, but the amplifier has not lost its sound parameters. After developing this circuit, I began making all my amplifiers for low-power speakers using this circuit.
The circuit of the presented amplifier has a wide range of reproducible frequencies, a supply voltage range 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 one, with a capacity from 0.01 to 4.7 μF (preferably from 0.1 to 0.47 μF), you can use both film and ceramic capacitors. It is advisable not to replace all other components.
Volume control from 10 to 47 kOhm.
The output power of the microcircuit allows it to be used in low-power speakers for PCs. It is very convenient to use the chip for stand-alone speakers for a mobile phone, etc.
The amplifier works immediately after switching on and does not require additional adjustment. It is recommended to additionally connect the power supply minus to the heat sink. It is advisable to use all electrolytic capacitors at 25 Volts.
The second circuit is assembled using 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, you can feel the entire frequency spectrum. With good headphones, it feels like you have a full-fledged subwoofer.
The amplifier is assembled with 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 at a low-impedance load, up to 4 ohms, which makes it possible to use the circuit to amplify the signal of a player, radio, etc. A 9-volt Krona battery is used as a power source.
The final stage also uses KT315 transistors. 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 amplifier power will reach up to 1 Watt. The output capacitor can have a capacity from 220 to 2200 µF.
The transistors in this circuit do not heat up, therefore, no cooling is needed. If you use larger output transistors, you may need small heat sinks for each transistor.
And finally - the third scheme. An equally simple, but proven version of the amplifier structure is presented. The amplifier is capable of operating from reduced voltage to 5 volts, in which case the PA output power will be no more than 0.5 W, and the maximum power with a 12 volt supply reaches up to 2 Watts.
The output stage of the amplifier is built on a domestic complementary pair. The amplifier is regulated by selecting resistor R2. To do this, it is advisable to use a 1 kOhm trimmer. Slowly rotate the regulator until the quiescent current of the output stage is 2-5 mA.
The amplifier does not have high input sensitivity, so it is advisable to use a pre-amplifier before the input.
The diode plays a significant 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 corresponding parameters, for example KT816/817. The amplifier can power low-power stand-alone speakers with a load resistance of 6-8 ohms.
List of radioelements
| Designation | Type | Denomination | Quantity | Note | Shop | My notepad | |
|---|---|---|---|---|---|---|---|
| Amplifier on TDA2003 chip | |||||||
| Audio amplifier | TDA2003 | 1 | To notepad | ||||
| C1 | 47 uF x 25V | 1 | To notepad | ||||
| C2 | Capacitor | 100 nF | 1 | Film | To notepad | ||
| C3 | Electrolytic capacitor | 1 uF x 25V | 1 | To notepad | |||
| C5 | Electrolytic capacitor | 470 uF x 16V | 1 | To notepad | |||
| R1 | Resistor | 100 Ohm | 1 | To notepad | |||
| R2 | Variable resistor | 50 kOhm | 1 | From 10 kOhm to 50 kOhm | To notepad | ||
| Ls1 | Dynamic head | 2-4 Ohm | 1 | To notepad | |||
| Transistor amplifier circuit No. 2 | |||||||
| VT1-VT3 | Bipolar transistor | KT315A | 3 | To notepad | |||
| C1 | Electrolytic capacitor | 1 uF x 16V | 1 | To notepad | |||
| C2, C3 | Electrolytic capacitor | 1000 uF 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 | 10 uF x 16V | 3 | ||||
I would like to present the design of a simple but powerful low-frequency amplifier, made using modern inexpensive transistors. The main advantages of this amplifier are ease of assembly, accessible and cheap radio components, and the finished amplifier does not require adjustment and works immediately. The amplifier develops very high power compared to similar circuits. Among the electrical parameters, I would like to note the very high linearity in the operating frequency range from 20Hz to 20kHz. True, it was not without its shortcomings either. This circuit has an increased noise level at high volumes, but if you take into account the simplicity and accessibility, it is still worth assembling an amplifier, I especially advise car enthusiasts for a powerful subwoofer, since the power of such a circuit is quite sufficient to drive high-power imported heads. From the diagram it is clear that it couldn’t be simpler. The circuit uses only 5 transistors and several additional radio components.
To reduce the noise level of the amplifier, you will need to install a variable resistor at the input with a resistance of 20 to 100 kOhm; they will also control the volume. In this case, at low volume there will be practically no noise, and at high volume we hardly hear the noise, and if the amplifier operates 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 4 Ohm.................................... ..150W
Input sensitivity Uin.................................................... ........................1B
Total coefficient of all types of distortion at P=60W 4Ohm, Kd........................0.005%
Amplifier quiescent current Ixx.................................................... ....................................20-25mA
Quiescent current of the output stage.................................................... ........................0mA
Reproducible frequency band at –3dB level, Hz,................................5-100,000
The parameters are quite good, the only obstacle to using the circuit as a car amplifier is the increased bipolar power supply, but this is not such a big obstacle, since many voltage converter circuits are known today, one of such circuits is based on the TL494 chip. The circuit is standard and allows you to get up to 200 watts of power at the transformer output, which is quite enough for the full operation of this homemade amplifier. I don’t show the converter circuit, since this is a completely different topic.
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