This article will discuss the circuit of a sound amplifier for domestic use. Depending on which area the amplifier will be used in (it is also called ULF - low frequency amplifier ), it will have different dimensions and the complexity of constructing the circuit. The article will touch upon three types of amplifiers at once - on transistors, microcircuits, and lamps. And it’s worth starting with the latter.
Tube ULF
Such can often be found in old equipment - televisions, radios. Despite the obsolescence, this technique is still popular with music lovers. There is an opinion that the tube sound is much cleaner and more beautiful than the "digitized" one. It is quite possible, in any case, such an effect as from lamps cannot be achieved using transistor circuits. It is worth noting that the sound amplifier circuit (the simplest, using lamps) can be implemented on only one triode.
In this case, it is necessary to apply a signal to the grid of the radio tube. The bias voltage is applied to the cathode - it is corrected by selecting the resistance in the circuit. A voltage (over 150 volts) is supplied to the anode through a capacitor and the primary winding of the transformer. Accordingly, the secondary winding is connected to the speaker. But this is a simple circuit, and in practice, two- or three-stage constructions are often used, in which there is a preliminary and terminal amplifier (on high-power lamps).
Disadvantages and advantages of lamp designs
What can be the disadvantage of lamp technology? It was mentioned above that the anode voltage must be above 150 volts. In addition to this, the presence of an alternating voltage of 6.3 V is mandatory for powering the filament of lamps. Sometimes 12.6 V is required, since there are lamps with such a voltage. Hence the conclusion - a huge power supply circuit, the need to use massive transformers.
But there are pluses that distinguish lamp technology from transistor: ease of installation, durability, it is almost impossible to disable the entire circuit. Unless you need to break the cylinder of the lamp to break it. You can not say about transistors - an excessively heated soldering iron tip or static can easily destroy the transition structure. The same problem is with microchips.
Transistor circuits
Above is a transistor sound amplifier circuit. As you can see, it is quite complex - it uses a large number of components that allow the entire system to work. But if you break them down into small components, it turns out that not everything is so complicated. And the whole circuit works in almost the same way as described above on a vacuum triode. In fact, a semiconductor transistor is nothing more than a triode.
The simplest design is a single semiconductor circuit, to the base of which three voltages are applied at once: from the plus of the power supply through the resistance is positive and from the common wire is negative, as well as from the signal source. The amplified signal is removed from the collector. Above is an example of a sound amplifier circuit (the simplest on transistors). It is not used in its pure form.
Microchips
The amplifier on microcircuits will be much more modern and better. Fortunately today there are a great many of them. The simplest circuit of a sound amplifier on a chip contains an extremely small number of elements. And any person who knows how to handle a soldering iron more or less tolerably can make a good ULF on their own. As a rule, microcircuits contain a couple of capacitors and resistances.
All other elements necessary for work are in the crystal itself. But the most important thing is nutrition. For some designs, bipolar power supplies must be used. Often the problem arises precisely in them. Microcircuits that need such power, for example, are quite difficult to use for the manufacture of an automobile amplifier.
Useful "lotions"
Since the conversation has begun about amplifiers on microcircuits, it is worthwhile to mention that they can be used with timbral blocks. Especially for such devices, microcircuits are produced. They contain all the necessary components, it remains only to correctly install the entire device.
And you will have the opportunity to adjust the timbre of the sound of music. Together with the LED equalizer, it will be not only convenient, but also a beautiful means of visualizing sound. And the most interesting thing for car audio lovers is, of course, the ability to connect a subwoofer. But this should be devoted to a separate section, because the topic is interesting and informative.
A subwoofer is easy
To connect a low-frequency speaker (subwoofer), you need to make a separate monophonic amplifier. If you look at industrial designs of amplifiers, then in one case they have stereo and monophonic amplifiers. The first is connected to the speakers, and the second to the subwoofer. And in the second there is a small feature - a low-pass filter is assembled at the input . Depending on the price category, this filter can be adjustable or not. You can assemble a sound amplifier with your own hands, the circuit of which is made on microcircuits, in a matter of minutes, since there is nothing complicated about it.
The simplest low-pass filter is several resistances and capacitors connected according to the circuit shown above. When this circuit is turned on, a signal with a certain frequency in the range of 30-60 Hertz is applied to the amplifier input. It is this frequency that is amplified by the ULF and transmitted to the woofer. It is worth noting that at the input of the low-pass filter, you must set the volume control.
Advantages of modern chip amplifiers
Having considered all possible types of amplifiers, we can conclude: the highest quality and simplest are made only on a modern element base. A lot of chips are produced specifically for low-frequency amplifiers. An example is the VLF type TDA with various digital designations.
They are used almost everywhere, as there are both low-power and powerful microcircuits. For example, for portable computer speakers, it is best to use microcircuits whose power is not higher than 2-3 watts. But for automotive equipment or home theater acoustics, it is desirable to use microcircuits with a power of more than 30 watts. But pay attention to the fact that sound power amplifiers need protection. The circuits must contain a fuse that protects against a short circuit in the circuit.
The plus is that a massive power supply is not required, so you can use a ready-made one, for example, from a laptop, PC, old MFPs (for new ones, as a rule, the power supply is inside). Ease of installation - this is what is important for beginner hams. The only thing required for such devices is high-quality cooling. If we are talking about a powerful technique, then you have to install a forced one - one or more coolers on a radiator.