Many people are familiar with the situation when some device plays 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 frequency power amplifier (hereinafter UMZCH). Moreover, the amplifier can be assembled by hand.
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.
The following will describe the most important parameters of audio power amplifiers that should be improved in order to achieve greater gain, as well as the simplest circuits of these devices, assembled on various basic components such as vacuum tubes, transistors, operational amplifiers and integrated circuits.
In addition, the article will consider a high-quality UMZCH scheme. Its composition, parameters, as well as design features will be affected. The UMZCH Sukhov scheme will also be considered.
UMZCH parameters
The most important parameter of the amplifierpower - amplification factor. It represents the ratio of the output signal to the input signal and is divided into three separate parameters:
- Current gain. KI=Iout / Iin.
- Voltage gain. KU=Uout / Uin.
- Power gain. KP=Pout / Pin.
In the case of UMZCH, it is more reasonable to consider the power gain, since it is this parameter that requires amplification, although it is foolish to deny that the power value - both input and output - depends on the current and voltage values.
Of course, amplifiers have other parameters such as the distortion factor of the amplified signal, but they are not so important compared to the gain.
Don't forget that there are no perfect 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
Electrovacuum devices are devices that contain 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 an anode.
Inside the flask there can be three, five, and even eight additional electrodes. 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.
Vacuum tube power amplifiersvery highly regarded among both ordinary music lovers and professional musicians, because tubes provide the "cleanest" amplification.
This is partly due to the fact that electrons injected from the cathode encounter no resistance on their way to the anode and reach the target in an unchanged state - they are not modulated in either density or speed.
Tube amplifiers are the most expensive of all that are on the market. This is due to the fact that electrovacuum devices were no longer widely used in the last century, respectively, their production in large quantities became unprofitable. This is a piece product. But such UMZCHs are definitely worth their money: in comparison with popular counterparts, even on integrated circuits, the difference is clearly audible. And not in favor of chips.
Of course, it is not necessary to assemble tube amplifiers on your own, you can purchase them in specialized stores. The cost of amplifiers on vacuum devices starts from ₽50,000. You can find relatively cheap used options (even up to ₽10,000), but they may be of poor quality. How much do good tube amps cost? From ₽100,000. How much do very good amplifiers cost? From several hundred thousand rubles.
There are a lot of UMZCH circuits on lamps, this section will consider an elementary example.
The simplest amplifier can be assembled on a triode. It belongs to the class of single-cycle UMZCH circuits. In a 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 eitherreduce 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 amount of amplification of current and voltage (in the end - power) of this electrovacuum device.
To assemble a simple triode amplifier, you need to connect a variable power source to the control grid, apply zero potential to the cathode, 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, you can connect a filter capacitor in series or in parallel (depending on the specific case) to the load, connect a capacitor and a resistor connected in parallel to the cathode, and connect a simple voltage divider of two resistors to the control grid.
Theoretically, a power amplifier can be assembled on a klystron according to UMZCH circuits on lamps. A klystron is an electrovacuum device, similar in design to a diode, but having two additional terminals that serve to input and output a signal. Amplification in this device occurs due to the modulation of the flow of electrons emitted by the cathode towards the collector (analogous to the anode), first in speed and then in density.
UMZCH on bipolar transistors
Bipolar transistor - synthesis of two diodes. It is either a p-n-p or n-p-n element with the following components:
- emitter;
- base;
- collector.
The speed and reliability of transistors is generally higher than that of vacuum 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 n-p-n transistor in a power amplifier circuit will be considered. It is important to note that electrons (n) are slightly faster than holes (p), respectively, the performance of n-p-n and p-n-p transistors differs not in favor of the latter.
Another important nuance is that bipolar transistors have several switching circuits:
- Common emitter (most popular).
- With a common base.
- With a common manifold.
All circuits have different gain parameters. The following UMZCH circuit has a common emitter connection.
To assemble a simple amplifier based on an n-p-n transistor, you need to connect an alternating voltage to its base, a positive potential to the collector, and a negative potential to the emitter. And in front of the base, and in front of the collector, and in front of the emitter, limiting resistances should be installed. The load is removed between the collector ballast and the collector itself.
As in the case of the electrovacuumtriode amplifier, to improve the quality of amplification in this circuit, you can:
- install a voltage divider and a filter capacitor in front of the base;
- install a capacitor and resistor connected in parallel to the emitter;
- turn on the filter capacitor to the load to eliminate noise and interference.
If two such amplifying stages are connected in series, then their gains can be multiplied by each other. This, of course, significantly complicates the design of the device, but it will allow to achieve greater amplification. True, it will not work to connect these cascades indefinitely: the more single amplifiers are connected in series, the greater the chance that they will go into saturation.
If the transistor operates in saturation mode, then there can be no talk of any amplifying properties. You can verify this by looking at the current-voltage characteristic: the operating point of the transistor is in the horizontal section if it operates in saturation mode.
UMZCH FET
Next, the UMZCH circuit on MOS type transistors (metal-oxide-semiconductor - the standard structure of a field-effect transistor) will be shown.
The structure of field-effect transistors has little in common with bipolar transistors. Moreover, their principle of operation is nothing like the principle of operation of bipolar analogs.
Field-effect transistors are controlled by an electric field (bipolar - by current). They draw no current and are resistant to gamma radiation, also calledradioactive radiation. The latter fact is unlikely to ever come in handy for musicians who want to build an audio power amplifier, but in the industry this feature of field-effect transistors is highly valued.
Their main disadvantage is that they do not interact well with static electricity. A charge of this nature of origin can disable transistors of this type. Any careless finger touch to the contact of the element can damage the transistor.
These features should be taken into account when assembling power amplifiers on these electronic components.
How to assemble a UMZCH circuit on a field-effect transistor with your own hands? It is enough to follow further instructions.
A simple UMZCH circuit on a field-effect transistor can be assembled using a p-n-junction field-effect transistor with an n-type channel. The design is similar to that described when assembling an amplifier on a bipolar transistor, only the gate took the place of the base, the collector - the drain, the emitter - the source.
UMZCH on an operational amplifier
An operational amplifier (hereinafter OU) is an electronic component that has two inputs - inverting (changes the signal in 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 power supply. It has a low zero offset voltage and input currents. This unit has a very high gain.
OU can operate in two modes:
- in amp mode;
- in modegenerator.
In order for the op-amp to work in amplifying mode, it is necessary to connect a negative feedback circuit to it. It is a resistor, which is connected with one output to the output of the op-amp, and the other - to the inverting input.
If you connect the same circuit to a non-inverting input, you will get a positive feedback circuit and the op-amp will start working as a signal generator.
There are several types of amplifiers assembled on the op-amp:
- Inverting - amplifies the signal and changes its phase by 180 degrees. To get an inverting amplifier on an op-amp, you need to ground the non-inverting input of the op-amp, and apply a signal to the inverting one that needs to be amplified. In this case, we must 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 pin of the op-amp.
- Differential - amplifies differential signals (signals that differ in phase but are the same in amplitude and frequency). To get a differential amplifier, you need to connect limiting resistors to the inputs of the op-amp, do not forget about the negative feedback circuit and apply two signals to the input contacts: a positive polarity signal must be applied to a non-inverting input, a negative signal to an inverting one.
- Measuring - a modified version of the differential amplifier. An instrumentation amplifier performs the same function as a differential amplifier, onlyhas the ability to adjust the gain using a potentiometer connecting the inputs of two op-amps. The design of such an amplifier is much more complicated and includes not one, but three op-amps.
How difficult is it to work with operational amplifiers? For op-amp circuits, it can sometimes be difficult to find suitable components such as resistors and capacitors, because careful matching of elements is required not only in nominal values, but also in materials.
UMZCH on integrated circuits
Integrated circuits are devices specially designed to perform a particular task. In the case of UMZCH, one small microcircuit replaces a large cascade of transistors, operational amplifiers or vacuum devices.
Currently, TDA chips with different serial numbers, such as 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 1 or 2 ruble coins.
Designing UMZCH
Before purchasing the necessary parts and etching the conductors on the textolite board, it is necessary to clarify the values of resistors and capacitors, as well as select the desired models of transistors, operational amplifiers or integrated circuits.
This can be done on a computer using dedicated software such as NI Multisim. ATThis program has collected a large database of electronic components. With its help, you can simulate the operation of any electronic devices, even taking into account errors, check circuits for operability.
With the help of such software, it is especially convenient to test powerful UMZCH circuits.
200W transistor stereo amplifier circuit
The scheme considered in this section is much more complicated than those described above. But its amplifying properties are better than those of designs based on bipolar, field-effect transistors, as well as operational amplifiers and integrated circuits, which have already been cited in the article.
This product includes the following items:
- Resistors.
- Capacitors (both polar and non-polar).
- Diodes.
- Zener diode.
- Fuses.
- N-p-n-type bipolar transistors.
- P-n-p bipolar transistors.
- P-Channel IGFETs.
- Insulated gate n-channel field-effect transistors.
Parameters of this power amplifier:
- Prated output=200W (per channel).
- Uoutput stage power=50V (slight variation allowed).
- Ioutput stage rest=200 mA.
- Irest of one output transistor=50 mA.
- Usensitivity=0.75 V.
All main parts of this device (transformer, systemcooling 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 volume control knobs are made of the same material.
A transformer with two windings of 35 V can be purchased ready-made. It is desirable to choose a core of a toroidal shape (its performance has been verified in this circuit), and the power should be 300 W.
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 UMZCH power supply circuit is given in the same section.
Three simple truths to remember when assembling any electrical circuit:
- Be sure to observe the polarity of polar capacitors. If you confuse plus and minus in a small amplifier circuit, then nothing terrible will happen, the UMZCH circuit simply will not work, but it was precisely because of such an insignificant, at first glance, error that rockets with equipment and crew on board fell.
- Be sure to observe the polarity of the diodes: the cathode with the anode is also forbidden to be interchanged. For a zener diode, this rule is also relevant.
- The main thing is that you need to solder parts only where there is a contact point on the diagram. Most faulty electrical circuits do not work precisely because the installer did not solder the parts or soldered them where they were not needed.
Is this scheme included in one of the best UMZCH schemes? Maybe. It all depends ondesires 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 connections, there is a high chance of making a mistake, due to which all significant amount of work will have to be redone.
Actually, the scheme given in this section is not correct to call Sukhov's scheme. This is a high-fidelity UMZCH of the VVS-2011 model (a schematic diagram of the UMZCH of this type is given in this section). In its composition, it does not contain field-effect transistors, but it includes:
- Zener diodes.
- Nonlinear resistors.
- Regular resistors.
- Polar and non-polar capacitors.
- Diodes.
- Bipolar transistors of both types.
- OpAmps.
- Throttle.
Possibilities of this inclusion:
- P=150W at Rload=8 ohm.
- Linearity: 0.0002 to 0.0003% at 20kHz, P=100W and Rload=4 ohm.
- Support for constant U=0 V.
- Available AC wire resistance compensation.
- Presence of current protection.
- Presence of protection of the UMZCH circuit from Uexit=const.
- Availability of soft start.
This circuit is assembled on an industrial scale and fits on a small board. The layout of the conductors and the location of the elements can be found on the Internet,where these materials are freely available.
Schemes of the Sukhov series are one of the best UMZCH schemes.
Result
A sound power amplifier is a very popular device among both professional musicians and ordinary music lovers. UMZCH are performed both on the basis of vacuum devices and transistors, and on the basis of operational amplifiers, integrated circuits.
Such devices can be purchased at specialized stores, or you can make your own. In terms of price, tube amplifiers are the most expensive, and integrated circuits are the cheapest.
UMZCH tube circuits have a higher gain quality than integrated or transistor UMZCH circuits. It is for this reason that people are ready to buy such devices for ₽50,000, and for ₽100,000, and for ₽450,000.
When assembling amplifiers yourself, remember the following rules:
- It is strictly forbidden to confuse the polarities of diodes, zener diodes and other anode-cathode devices, as well as polar capacitors. This is fraught with the fact that the UMZCH circuit assembled as a result will not work.
- When assembling the circuit, you need to solder the parts where there is a point of contact on the drawing. Sounds like the obvious rule. This is true, but many installers forget about it.
If you use all the recommendations given above, you can assemble a good sound power amplifier yourself according to the UMZCH circuit on transistors or other elements.
