Many people are familiar with the situation when a device reproduces sound, but does not do it as loudly as we would like. What to do? You can buy other sound reproducing equipment, or you can purchase an audio power amplifier (hereinafter UMZCH). Moreover, the amplifier can be assembled with your own hands.
To do this, you only need basic knowledge of electronics, such as the ability to distinguish between the emitter, base and collector in a bipolar transistor, drain, source, gate in the field, as well as other elementary aspects.
Hereinafter, the most important parameters of sound power amplifiers will be described, the improvement of which is worth working to achieve greater gain, as well as the simplest circuits of these devices collected on various main components such as electronic lamps, transistors, operational amplifiers and integrated circuits.
In addition, the article will consider the scheme of high-quality UMZCH. Its composition, parameters, as well as structural features will be affected. Also, the scheme of UMZCH Sukhov will be considered.
UMZCH parameters
The most important parameter of a power amplifier is the gain. It represents the ratio of the output signal to the input and is divided into three separate parameters:
- Current gain. K I = I out / I in .
- Voltage gain K U = U o / U in .
- Power gain. K P = P out / P in .
In the case of UMZCH, it is more reasonable to consider the power gain, since this parameter needs to be amplified, although it is foolish to deny that the power value, both input and output, depends on the current and voltage.
Of course, amplifiers also have other parameters, such as the distortion coefficient of the amplified signal, but all of them are not so important compared to the amplification factors.
Do not forget that there are no ideal devices. There is no UMZCH with a huge gain, devoid of other disadvantages. You always have to sacrifice some parameters for the sake of others.
UMZCH on electrovacuum devices
Vacuum devices are devices containing in their design a flask in which there is either a vacuum or a certain gas, as well as at least two electrodes - a cathode and anode.
Three, five, and even eight additional electrodes can be inside the bulb. A lamp with two electrodes is called a diode (not to be confused with a semiconductor diode), with three - a triode, with five - a pentode.
Power amplifiers on electronic tubes are very much appreciated both among ordinary music lovers and among professional musicians, because lamps give the most “pure” amplification.
This is partly due to the fact that the electrons injected from the cathode do not encounter resistance on the way to the anode and reach the target in an unchanged state - they are not modulated either in density or in speed.
Tube amplifiers are the most expensive of all that are on the market. This is due to the fact that electro-vacuum devices ceased to be used in large quantities in the last century, respectively, the release of them in large batches became unprofitable. This is a piece product. But such UMZCH are definitely worth the money: in comparison with popular analogs, even on integrated circuits, the difference is clearly visible. And not in favor of chips.
Of course, it is not necessary to assemble tube amplifiers yourself, you can purchase them in specialized stores. The cost of amplifiers on electric vacuum devices starts from ₽50,000. You can find relatively cheap used options (even up to ₽10,000), but they can be of poor quality. How much do good lamp amplifiers cost? From ₽100,000. How much are very good amplifiers? From several hundred thousand rubles.
There are a lot of UMZCH schemes on lamps, in this section an elementary example will be considered.
The simplest amplifier can be assembled on a triode. It belongs to the class of single-cycle UMZCH circuits. In the triode, the third electrode is a control grid that regulates the anode current. An alternating voltage is connected to it and using the magnitude and polarity of the source signal, you can either reduce or increase the anode current.
If you connect a negative high potential to the grid, then the electrons will settle on it and the current in the circuit will be zero. If a positive potential is applied to the grid, then the electrons from the cathode to the anode will pass unhindered.
By adjusting the anode current, you can change the operating point of the triode on the current-voltage characteristic. This allows you to adjust the magnitude of the current and voltage gain (in the end - power) of this electrovacuum device.
To assemble the simplest amplifier on the triode, you need to connect an alternating power source to the control grid, apply zero potential to the cathode, and positive to the anode. Ballast resistance is usually connected to the anode. The load should be removed between the ballast and the anode.
To improve the quality of the amplified signal, a filter capacitor can be connected in series or in parallel (depending on the specific case), a capacitor and a resistor connected in parallel to the cathode, and a simple voltage divider of two resistors connected to the control grid.
Theoretically, a power amplifier can be assembled on a klystron according to UMZCH schemes on lamps. Klystron is an electrovacuum device, similar in design to a diode, but having two additional terminals, used to input and output a signal. The amplification in this device is due to the modulation of the flow of electrons emitted by the cathode towards the collector (anode analog), first in speed and then in density.
UMZCH on bipolar transistors
A bipolar transistor is a synthesis of two diodes. It is either a pnp or npn element with the following components:
The speed and reliability of transistors is generally higher than that of electrovacuum devices. It's no secret that at first electronic computers worked precisely on lamps, but as soon as transistors appeared, the latter quickly replaced their antediluvian competitors and are successfully used to this day.
Next, an example of using an npn transistor in a power amplifier circuit will be considered. It is important to note that the electrons (n) are slightly faster than the holes (p), respectively, the speed of npn and pnp transistors differs not in favor of the latter.
Another important nuance is that bipolar transistors have several switching circuits:
- With a common emitter (the most popular).
- With a common base.
- With a common collector.
All circuits have different gain parameters. The following UMZCH circuit has an inclusion with a common emitter.
To assemble the simplest amplifier on an npn transistor, you need to connect alternating voltage to its base, to the collector - positive potential, and to the emitter - negative. And in front of the base, and in front of the collector, and in front of the emitter, limit resistance should be established. The load is removed between the ballast of the collector and the collector itself.
As in the case of an electric vacuum amplifier on a triode, to improve the quality of amplification in this circuit, you can:
- install a voltage divider and filter capacitor in front of the base;
- install a parallel connected capacitor and resistor to the emitter;
- turn on the filter capacitor to the load to eliminate noise and interference.
If two such amplification stages are connected in series, then their amplification factors can be multiplied by each other. This, of course, will significantly complicate the design of the device, but will allow for greater gain. True, these cascades cannot be connected endlessly: the more single amplifiers are connected in series, the greater the chance that they will go into saturation.
If the transistor is operating in saturation mode, then there can be no talk of any amplifying properties. This can be seen if you look at the current-voltage characteristic: the operating point of the transistor is on a horizontal section, if it works in saturation mode.
UMZCH on a field effect transistor
Next, a UMZCH circuit for MOS transistors (metal-oxide-semiconductor - a standard structure of a field-effect transistor) will be given.
The structure of field effect transistors has little in common with bipolar transistors. Moreover, their principle of operation is in no way similar to the principle of action of bipolar analogues.
Field effect transistors are controlled by an electric field (bipolar - by current). They do not consume current and are resistant to gamma radiation, which is also called radioactive radiation. The latter fact is unlikely to ever come in handy for musicians who want to assemble a sound power amplifier, but in industry this feature of field-effect transistors is highly appreciated.
Their main disadvantage is that they interact poorly with static electricity. A charge of this nature of origin can damage transistors of this type. Any careless finger touch before the contact of the element can damage the transistor.
These features should be considered when assembling power amplifiers on these electronic components.
How to assemble a do-it-yourself UMZCH circuit on a field effect transistor? It is enough to follow the further instructions.
A simple UMZCH circuit on a field effect transistor can be assembled using a field effect transistor with a pn junction with an n-type channel. The design is similar to that described when assembling the amplifier on a bipolar transistor, only the gate took the place of the base, the collector - drain, the emitter - source.
UMZCH on the operational amplifier
An operational amplifier (OA) is an electronic component that has two inputs - inverting (changes the signal phase by 180 degrees) and non-inverting (does not change the phase of the signal) - as well as one output and a pair of contacts for supplying power. It has a small value of zero bias voltage and input currents. This device has a very high gain.
Shelter can work in two modes:
- in amplifier mode;
- in generator mode.
In order for the op-amp to operate in amplifier mode, it is necessary to connect a negative feedback circuit to it. It is a resistor, which is connected to the output of the op-amp by one output, and the inverting input by the other.
If you connect the same circuit to a non-inverting input, you get a positive feedback circuit and the op-amp starts working as a signal generator.
There are several types of amplifiers assembled on an op-amp:
- Inverting - amplifies the signal and changes its phase by 180 degrees. To get an inverting amplifier at the op-amp, you need to ground the non-inverting input of the op-amp, and send an signal to the inverting amplifier, which needs to be amplified. At the same time, one should not forget about the negative feedback circuit.
- Non-inverting - amplifies the signal without changing its phase. To assemble a non-inverting amplifier, you need to connect a negative feedback circuit to the op-amp, ground the inverting input and apply a signal to the non-inverting contact of the op-amp.
- Differential - amplifies differential signals (signals that differ in phase, but are identical in amplitude and frequency). To obtain a differential amplifier, it is necessary to connect limiting resistors to the op amp inputs, do not forget about the negative feedback circuit and apply two signals to the input contacts: a signal of positive polarity must be fed to a non-inverting input, and negative to an inverting one.
- Measuring - A modified version of a differential amplifier. The measuring amplifier performs the same function as the differential one, it only has the ability to adjust the gain with a potentiometer connecting the inputs of two op-amps. The design of such an amplifier is noticeably more complicated and includes not one, but three op-amps.
What is the complexity of working with operational amplifiers? For circuits with op-amps, it is sometimes difficult to choose suitable components like resistors and capacitors, because careful coordination of elements is required not only in nominal values, but also in materials.
UMZCH on integrated circuits
Integrated circuits - devices specifically designed to perform a particular task. In the case of UMZCH, one small microcircuit replaces a large cascade of transistors, operational amplifiers or electrovacuum devices.
Currently, TDA chips with various serial numbers, for example, TDA7057Q or TDA2030, are very popular. There are a huge number of UMZCH circuits on microcircuits.
In their composition they have a large number of resistors, capacitors and operational amplifiers, equipped in a very small case, the size of which does not exceed coins of 1 or 2 rubles.
Design UMZCH
Before you purchase the necessary parts and etch the conductors on the PCB board, you need to clarify the values of the resistors and capacitors, as well as select the necessary models of transistors, operational amplifiers or integrated circuits.
This can be done on the computer using special software, for example, NI Multisim. This program contains a large database of electronic components. With its help, you can simulate the operation of any electronic devices, even taking into account errors, check the circuit for operability.
Using such software, it is especially convenient to test powerful UMZCH circuits.
Stereo amplifier circuit for 200 W transistors
The scheme discussed in this section is much more complicated than those described above. But its amplifying properties are better than that of designs on bipolar, field-effect transistors, as well as operational amplifiers and integrated circuits, which are already given in the article.
The composition of this device includes the following elements:
- Resistors
- Capacitors (both polar and non-polar).
- Diodes.
- Zener diode
- Circuit breakers.
- NPN type bipolar transistors.
- PNP type bipolar transistors.
- Insulated gate field effect transistors with p-type channel.
- N-type insulated gate field effect transistors.
Parameters of this power amplifier:
- P rated output = 200 W (for each channel).
- U power supply of the output stage = 50 V (slight deviation is permissible).
- I rest of the output stage = 200 mA.
- I rest of one output transistor = 50 mA.
- U sensitivity = 0.75 V.
All the main parts of this device (transformer, cooling system in the form of radiators and the board itself) are located on an anodized chassis made of sheet duralumin, the thickness of which is 5 mm. The front panel of the device and the volume control knobs are made of the same material.
A transformer with two 35 V windings can be purchased ready-made. It is advisable to choose a toroidal core (its performance in this circuit has been verified), and the power should be 300 watts.
The power supply for the circuit will also have to be assembled independently according to the UMZCH power circuit. To construct it, you will need a fuse, a transformer, a diode bridge, as well as four polar capacitors.
The circuit of the power supply UMZCH is given in the same section.
Three simple truths to remember when assembling any electrical circuit:
- Be sure to observe the polarity of the polar capacitors. If you mix up the plus and minus in a small amplifier circuit, then nothing bad will happen, the UMZCH circuit simply will not work, but it was because of such a seemingly insignificant error that missiles with equipment and crew fell on board.
- Be sure to observe the polarity of the diodes: the cathode with the anode is also forbidden to interchange. For the zener diode, this rule is also relevant.
- The main thing is to solder parts only where there is a contact point on the circuit. Most faulty electrical circuits do not work precisely because the installer did not solder the parts or solder them where it is not needed.
Is this scheme one of the best UMZCH schemes? Maybe. It all depends on the desires of the consumer.
Sukhov's scheme
If the previous power amplifier circuit can be assembled independently, because it includes relatively few elements, then it is better not to assemble the Sukhov amplifier circuit manually. Why? Due to the huge number of elements and compounds, there is a great chance of making a mistake, because of which you will have to redo the entire significant amount of work.
In fact, the scheme given in this section is incorrectly called the Sukhov scheme. This is UMZCH of high fidelity of the VVS-2011 model (a schematic diagram of UMZCH of this type is given in this section). In its composition, it does not contain field-effect transistors, but it includes:
- Zener diodes.
- Non-linear resistors.
- Conventional resistors.
- Polar and non-polar capacitors.
- Diodes.
- Bipolar transistors of both types.
- Operational amplifiers.
- Throttle.
Features of this inclusion:
- P = 150 W at R load = 8 Ohms.
- Linearity: from 0.0002 to 0.0003% at a frequency of 20 kHz, P = 100 W and R load = 4 Ohms.
- The presence of constant support U = 0 V.
- The presence of compensation for the resistance of wires with alternating current.
- The presence of current protection.
- The presence of protection circuit UMZCH from U output = const.
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Total
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UMZCH tube circuits have a higher gain quality than integrated or transistor UMZCH. It is for this reason that people are ready to buy such devices for both $ 50,000, and for $ 100,000, and for $ 450,000.
When assembling the amplifiers yourself, it is worth remembering the following rules:
- It is strictly forbidden to confuse the polarity of diodes, zener diodes and other anode-cathode devices, as well as polar capacitors. This is fraught with the fact that the ultimately assembled UMZCH circuit will not work.
- When assembling the circuit, solder the parts where there is a contact point in the drawing. Sounds like an obvious rule. This is true, but many installers forget about it.
If you use all the recommendations listed above, you can assemble a good sound power amplifier yourself according to the UMZCH scheme for transistors or other elements.