If you are faced with the problem of choosing an amplifier and cannot decide on a ready-made device, but at the same time you know a little about electronics, I advise you to try to assemble a low-frequency audio amplifier (ULF) with your own hands. Amplifiers are very different both in complexity and in the type of construction.
Tube ULF
Low-frequency tube amplifiers are found in old television and radio equipment. Even after this technique is hopelessly outdated, music lovers simply adore tube amplifiers. There is an opinion that the sound emitted by tube ULFs is much more beautiful and cleaner, there is such a thing as velvet sound. "Digitized" sounding modern ULF sounds more "dry". Of course, the sound of a tube amplifier can never be achieved if you use transistors when assembling. A circuit that is implemented using only one triode:
In the above diagram, the signal is fed to the tube grid. The bias voltage is applied to the cathode, this voltage is corrected by selecting the resistance in the circuit. The supply voltage, which is more than 150 volts, is fed through a capacitor to the primary winding of the transformer at the anode. Therefore, a secondary winding is connected to the speaker. This circuit is one of the simplest, most often in practice, devices with two-stage and three-stage designs are used, consisting of a preamplifier and an output amplifier based on powerful tubes.
Disadvantages and advantages of amplifiers assembled on tubes
Despite the simplicity of the design, tube amplifiers still have a number of disadvantages. First of all, as mentioned above, the mandatory presence of an anode voltage of more than 150 volts. Also, to power the lamp ULF, it is necessary to have an alternating voltage of 6, 3 volts, this is required to power the filaments of the radio tubes. If lamps with a filament voltage of 12.6 volts are used, then an alternating voltage of 12.6 volts is also required. Therefore, to power the amplifier on radio tubes, a power supply unit with a complex circuit is required, in which massive transformers must be used.
The advantages that distinguish the tube design of the amplifier from others are: durability, simple installation, the inability to disable the constituent components. Unless you try very hard and break the lamp, then the device will fail. What can not be said about the ULF assembled on transistors, there is enough of an overheated soldering iron tip or static voltage, and the likelihood of failure of some components increases significantly. A similar problem exists with designs on microcircuits.
Circuits assembled on transistors
Below is a schematic diagram of ULF audio assembled on transistors. At first glance, such a scheme looks rather complicated, due to the use of a large number of radio components that allow the device to work. But one has only to divide the circuit into its constituent blocks, then everything becomes very clear. This circuit has a similar operating principle as the above-described tube design on a triode. Here the semiconductor transistor plays the role of that very triode. The power of the device will directly depend on the selected components.
Putting together the simplest circuit on one transistor
Next, we will consider the simplest ULF design, consisting of one semiconductor. Please note that this circuit is a single channel amplifier. Let's give a schematic diagram of such an amplifier.
As an example, let's assemble the simplest sound device based on one transistor.
First, you should prepare the necessary components and equipment. For assembly you will need:
- · Silicon transistor of n-p-n type, for example, KT805, or its analogue.
- · An electrolytic capacitor with a capacity of 100 μF, its voltage must be 16 or more volts.
- · Variable resistor, with a resistance of about 5 kOhm.
- · Assembly board, if any. If not, you can assemble the device and surface mounting.
- · A radiator, this is a must, without it the transistor will quickly overheat and fail.
- · Wires for connecting components.
- · Mini-jack for connecting a sound source. It can be a computer or other device with an audio output, for example, it is possible to use a smartphone.
- · DC power supply 5-12 volts, it can be a power supply unit or a battery of the "crown" type.
- · Soldering iron for soldering elements, as well as solder and rosin or any other flux.
We will assemble our amplifier from components that have already seen life.
So, when all the components are selected, we begin the assembly. First, we place the components on the circuit board.
Next, the negative terminal of the capacitor and the central contact of the variable resistor must be soldered to the base of the transistor.
According to the diagram, we connect the plus of the power supply and the plus of the speaker to the second contact of the variable resistor. To do this, we bring the contact with a wire to the circuit board. The central contact of the transistor (collector) is the negative terminal of the speaker, we will also bring it to the board.
Then, to the remaining terminal of the transistor (emitter), you must connect the negative power, as well as the contact for the negative input signal. The positive terminal of the input signal is the positive leg of the capacitor.
The assembly is almost ready; to start testing, it remains to solder three pairs of wires. From left to right in the photo: entrance, exit, food. And also be sure to install a radiator on the transistor.
Then we start setting up our amplifier. To do this, we connect all the components, strictly observing the polarity. Also, before connecting, you must make sure that there is no short circuit, especially with a hinged assembly.
The adjustment is made by adjusting the variable resistor, thus the operation of the resistance of the speaker and the transistor is coordinated.
That's all, the assembly and setup of the simplest bass amplifier is complete. Accordingly, such an ULF is a mono amplifier, i.e. single-channel. To achieve stereo sound, you need to assemble two similar devices. It should be noted that such devices, assembled according to the simplest scheme, are not used anywhere due to their inexpediency. For domestic needs, more complex devices are needed.
ULF on microcircuits
An amplifier assembled on microcircuits will be of much better quality. There are now many ICs designed specifically for amplifiers. Such a device can already be used in everyday life. There are many schematic diagrams, and the simplest of them are quite accessible for assembly to almost anyone who has the desire and basic knowledge of working with a soldering iron. Typically, the microcircuit layout includes two or three capacitors and several resistors.
Below is a schematic diagram of such an amplifier.
Other components that are necessary for the operation of the ULF are in the chip itself. When assembling an amplifier on microcircuits, the most important thing is to pay attention to the power supply. Some circuits require a bipolar supply transformer. Very often problems arise in them. For example, such amplifiers are practically not used for car speakers. But they have perfectly proven themselves as stationary amplifiers for home use. A variety of capacities are also available here. With the help of microcircuits, it is quite possible to assemble both a low-power amplifier and achieve a colossal 1000W sound.
