When a woman comes to the store to buy shampoo, it is difficult for her to immediately decide on a purchase, and she spends hours wandering along the shelves, sorting through dozens of options. So many radio amateurs, taking on the task of assembling a homemade UMZCH, can spend a long time choosing among a wide variety of circuits and microcircuits. These are the weak ones TDA2282, and simple TDA1557, and serious TDA7294, and dear STK40... The choice provided by manufacturers of specialized audio integrated circuits is very large. Which one should I stop at? We offer an option that is rightfully considered the golden mean in amplifier construction - the TDA2050 chip (), which at a price of a couple of tens of rubles will provide us with an honest 30 watts of power. That in the stereo version there are already 60 is quite enough for an apartment.
Amplifier circuit for self-production
A printed circuit board has been developed for this device, which is suitable for TDA2050 or LM1875 and has all the necessary components - power supply, speaker protection, turn-on and quick turn-off delay. This is achieved using the UPC1237 microcircuit, which is convenient but not very popular in domestic markets. If it is not possible to buy it, simply remove all elements of its wiring from the circuit, starting from resistors R12, R13. Then, in terms of protection, you will rely on the UMZCH microcircuits themselves, which have thermal and short circuit protection. The truth is not very reliable. Yes, and clicks when turned on from the speakers are possible. The parameters of the amplifier itself are described in detail in the documentation.
M/s TDA2050 and LM1875 are completely interchangeable; the differences in their circuits are only the values of a pair of resistors and one capacitor.
All this allows you to make a universal printed circuit board suitable for any of these two microcircuits.
Supply voltage source
The UMZCH itself is 2x30 W, but the power depends on the supply voltage and the resistance of the speakers connected to the output. If you haven’t found a transformer capable of providing the specified bipolar power supply (2 x 17 V), it doesn’t matter. The circuit can also operate on a reduced voltage, for example 2 to 12 V. In this case, the power will simply drop proportionally. But such a transformer is easier to find - you can even take two standard ones, 12 V each, and connect their output windings in series.
As for all kinds of tone blocks, as practice has shown, this is an unnecessary complication of the circuit, which is fraught with unnecessary noise. You can also change the frequency response on a computer (phone). A regular volume control is sufficient here. And, as an option, channel balance.
Box for a homemade amplifier
The case in our case is plastic, with front and rear walls in the form of 1 mm metal plates. You can take absolutely any box suitable in size and design, be it plastic (easier to process and drill), or metal (protection from interference and strength).
All connectors are standard - 220 V network, RCA inputs and pedal outputs for speaker systems. Pay special attention to the resistor for the volume control. Before putting it into the VLF, just connect it and listen for any rustling or crackling sounds from the speakers when you turn the knob.
Discuss the article HOW TO MAKE AN AMPLIFIER WITH YOUR OWN HANDS
High input impedance and shallow feedback are the main secret of warm tube sound. It's no secret that the highest quality and most expensive amplifiers, which belong to the HI-End category, are manufactured using tubes. Let's understand what a quality amplifier is? A low-frequency power amplifier has the right to be called high-quality if it completely repeats the shape of the input signal at the output without distorting it; of course, the output signal is already amplified. On the Internet you can find several circuits of really high-quality amplifiers, which can be classified as HI-End and do not necessarily require tube circuitry. To obtain maximum quality, you need an amplifier whose output stage operates in pure class A. Maximum linearity of the circuit gives a minimum amount of distortion at the output, therefore, in the design of high-quality amplifiers, special attention is paid to this factor. Tube circuits are good, but not always available even for self-assembly, and industrial tube UMZCHs from branded manufacturers cost from several thousand to several tens of thousands of US dollars - this price is certainly not affordable for many.
The question arises - is it possible to achieve similar results from transistor circuits? the answer will be at the end of the article.
There are quite a lot of linear and ultra-linear circuits of low-frequency power amplifiers, but the circuit that will be considered today is a high-quality ultra-linear circuit, which is implemented with only 4 transistors. The circuit was created back in 1969 by British audio engineer John Linsley-Hood. The author is the creator of several other high-quality circuits, in particular class A. Some experts call this amplifier the highest quality among transistor ULFs, and I was convinced of this a year ago.
The first version of such an amplifier was presented at. A successful attempt at implementing the circuit forced me to create a two-channel ULF using the same circuit, assemble everything in a housing and use it for personal needs.
Features of the scheme
Despite its simplicity, the scheme has several features. Correct operation may be disrupted due to incorrect board layout, poor placement of components, incorrect power supply, etc.
It is the power supply that is a particularly important factor - I strongly advise against powering this amplifier from all kinds of power supplies; the best option is a battery or a power supply with a battery connected in parallel.
The amplifier power is 10 watts with a 16 Volt power supply into a 4 Ohm load. The circuit itself can be adapted for 4, 8 and 16 Ohm heads.
I created a stereo version of the amplifier, both channels are located on the same board.
Since the original transistors of the circuit could not be found, analogues had to be used. The entire base is domestic. The first transistor (where the sound is actually formed) was made of germanium; it sounds better by ear. You can use any P-N-P low-power germanium transistors MP25 and the like. If desired, the transistor can be replaced with KT361 or no less noisy ones.
The second one is intended for driving the output stage, I installed KT801 (it was quite difficult to get hold of it.
In the output stage itself, I installed powerful bipolar switches of reverse conduction - the KT803 received undoubtedly high-quality sound with them, although I experimented with many transistors - KT805, 819, 808, and even installed powerful composite switches - KT827, with it the power is much higher, but the sound is not compare with KT803, although this is just my subjective opinion.
An input capacitor with a capacity of 0.1-0.33 µF, you need to use film capacitors with minimal leakage, preferably from well-known manufacturers, the same with the output electrolytic capacitor.
If the circuit is designed for a 4 Ohm load, then you should not increase the supply voltage above 16-18 Volts.
I decided not to install a sound regulator; it, in turn, also affects the sound, but it is advisable to install a 47k resistor parallel to the input and minus.
The board itself is a prototype board. I had to tinker with the board for a long time, since the lines of the tracks also had some influence on the sound quality as a whole. This amplifier has a very wide range of reproduced frequencies, from 30 Hz to 1 MHz.
Setup couldn't be easier. To do this, you need to use a variable resistor to achieve half the supply voltage at the output. For more precise settings, you should use a multi-turn variable resistor. We connect one multimeter lead to the minus power supply, put the other one to the output line, i.e. to the plus of the electrolyte at the output, thus, slowly rotating the variable we achieve half of the power supply at the output.
The quiescent current of the amplifier is 0.5-0.7A and this is quite normal for class A. The efficiency of the circuit is no more than 25%, all the main power of the power supply turns into unnecessary heat, which is released by the transistors of the output stage, so they need intensive cooling, possibly You will also need a cooler.
I highly recommend that beginners assemble this circuit. I am not a master myself, but rather a beginner radio amateur. Well, I already know the basics of electronics, basic things, so I decided to try my hand at this design...It all started with the fact that I had long wanted to build myself an inexpensive, but quite powerful sound amplifier. Not on the simplest 1555
, which play no better than ordinary mini-speakers, but at least fifty watts. Well, I've reached my goal. Assembled an amplifier on a well-known microcircuit TDA7294. You can easily squeeze 100 W or more from it. I bought the microcircuit for only $1.5, and took everything else from a Soviet TV, I found almost everything there.
Microcircuit connection diagram
The advantage of this amplifier is that it is so tested and retested by thousands of radio amateurs that all beginners can assemble this circuit without any problems - there are no serious obstacles here. All parts can be found at home (except for the chip itself).
Power transformer TS-160 It is permissible to take it from the same TV, disassemble it, leave the primary, and wind the secondary with 172 turns of wire with a diameter of 1.5 mm. Low-power transformers are not suitable here (after all, you need 200 watts just for sound). The minimum power of the transformer must be over 100 watts if the microcircuit is powered by reduced voltage. It is known that the power supply of the microcircuit 7294
bipolar. The voltage was -+ 55 volts. Current 2-3 Amperes. To be honest, I didn’t measure the current consumption, that is, I forgot. I remembered when everything was soldered. The power wires need to be thicker. At high volumes, thin wires heat up and stick to each other, which actually causes a short circuit.
The diode bridge was taken from an imported TV, although the diodes got noticeably hot when playing sound. All other details were obtained from Soviet TV.
One more thing, the amplifier is equipped with a cooler, since the radiator was not very large. I assembled the diagram on a piece of cardboard. I didn't find any textolite at all. For many radio amateurs, such luxuries as textolite, vitriol, and a laser printer are not available. I’m also on this list:(But you can see that if you want to do something, you can get by with little.
The parts were connected with copper wires. I didn’t install LEDs or other indicators at all, since seriousness and performance are important to me in the first place. The speaker is currently 20-30 W, 8 Ohm. I haven't bought the 100 watt head yet.
Photo of the finished amplifier is above. Yes, accuracy is not in the best condition. But surprisingly, everything turned out very well - there are no audible distortions. The input signal was supplied from the telephone. The amplifier started up the first time I turned it on and that made me very happy! With uv. best.boy99
Discuss the article POWERFUL AMPLIFIER FOR BEGINNERS
- Protozoa
- Straight up
- Theoretical Interlude
- Lamps
- How to make a transformer?
- On microcircuits
- UMZCH for subwoofer
- Headphone amplifier
The neighbor started knocking on the radiator. I turned the music up so I couldn't hear him.
(From audiophile folklore).
The epigraph is ironic, but the audiophile is not necessarily “sick in the head” with the face of Josh Ernest at a briefing on relations with the Russian Federation, who is “thrilled” because his neighbors are “happy.” Someone wants to listen to serious music at home as in the hall. For this purpose, the quality of the equipment is needed, which among lovers of decibel volume as such simply does not fit where sane people have a mind, but for the latter it goes beyond reason from the prices of suitable amplifiers (UMZCH, audio frequency power amplifier). And someone along the way has a desire to join useful and exciting areas of activity - sound reproduction technology and electronics in general. Which in the age of digital technology are inextricably linked and can become a highly profitable and prestigious profession. The optimal first step in this matter in all respects is to make an amplifier with your own hands: It is UMZCH that allows, with initial training on the basis of school physics on the same table, to go from the simplest designs for half an evening (which, nevertheless, “sing” well) to the most complex units, through which a good rock band will play with pleasure. The purpose of this publication is highlight the first stages of this path for beginners and, perhaps, convey something new to those with experience.
Protozoa
So, first, let's try to make an audio amplifier that just works. In order to thoroughly delve into sound engineering, you will have to gradually master quite a lot of theoretical material and not forget to enrich your knowledge base as you progress. But any “cleverness” is easier to assimilate when you see and feel how it works “in hardware.” In this article further, too, we will not do without theory - about what you need to know at first and what can be explained without formulas and graphs. In the meantime, it will be enough to know how to solder with an electric soldering iron and use a multitester.
Note: If you haven’t soldered electronics yet, keep in mind that its components cannot be overheated! Soldering iron - up to 40 W (preferably 25 W), maximum allowable soldering time without interruption - 10 s. The soldered pin for the heat sink is held 0.5-3 cm from the soldering point on the side of the device body with medical tweezers. Acid and other active fluxes cannot be used! Solder - POS-61.
On the left in Fig.- the simplest UMZCH, “which just works.” It can be assembled using both germanium and silicon transistors.
On this baby it is convenient to learn the basics of setting up an UMZCH with direct connections between cascades that give the clearest sound:
- Before turning on the power for the first time, turn off the load (speaker);
- Instead of R1, we solder a chain of a constant resistor of 33 kOhm and a variable resistor (potentiometer) of 270 kOhm, i.e. first note four times less, and the second approx. twice the denomination compared to the original according to the scheme;
- We supply power and, by rotating the potentiometer, at the point marked with a cross, we set the indicated collector current VT1;
- We remove the power, unsolder the temporary resistors and measure their total resistance;
- As R1 we set a resistor with a value from the standard series closest to the measured one;
- We replace R3 with a constant 470 Ohm chain + 3.3 kOhm potentiometer;
- Same as according to paragraphs. 3-5, V. And we set the voltage equal to half the supply voltage.
Point a, from where the signal is removed to the load, is the so-called. midpoint of the amplifier. In UMZCH with unipolar power supply, it is set to half its value, and in UMZCH with bipolar power supply - zero relative to the common wire. This is called adjusting the amplifier balance. In unipolar UMZCHs with capacitive decoupling of the load, it is not necessary to turn it off during setup, but it is better to get used to doing this reflexively: an unbalanced 2-polar amplifier with a connected load can burn out its own powerful and expensive output transistors, or even a “new, good” and very expensive powerful speaker.
Note: components that require selection when setting up the device in the layout are indicated on the diagrams either with an asterisk (*) or an apostrophe (‘).
In the center of the same fig.- a simple UMZCH on transistors, already developing power up to 4-6 W at a load of 4 ohms. Although it works like the previous one, in the so-called. class AB1, not intended for Hi-Fi sound, but if you replace a pair of these class D amplifiers (see below) in cheap Chinese computer speakers, their sound improves noticeably. Here we learn another trick: powerful output transistors need to be placed on radiators. Components that require additional cooling are outlined in dotted lines in the diagrams; however, not always; sometimes - indicating the required dissipative area of the heat sink. Setting up this UMZCH is balancing using R2.
On the right in Fig.- not yet a 350 W monster (as was shown at the beginning of the article), but already quite a solid beast: a simple amplifier with 100 W transistors. You can listen to music through it, but not Hi-Fi, operating class is AB2. However, it is quite suitable for scoring a picnic area or an outdoor meeting, a school assembly hall or a small shopping hall. An amateur rock band, having such a UMZCH per instrument, can perform successfully.
Dynamics
The dynamic range of the UMZCH is determined by curves of equal loudness and threshold values for different degrees of perception:
- Symphonic music and jazz with symphonic accompaniment - 90 dB (110 dB - 20 dB) ideal, 70 dB (90 dB - 20 dB) acceptable. No expert can distinguish a sound with a dynamics of 80-85 dB in a city apartment from ideal.
- Other serious music genres – 75 dB excellent, 80 dB “through the roof”.
- Pop music of any kind and movie soundtracks - 66 dB is enough for the eyes, because... These opuses are already compressed during recording to levels of up to 66 dB and even up to 40 dB, so that you can listen to them on anything.
The dynamic range of the UMZCH, correctly selected for a given room, is considered equal to its own noise level, taken with the + sign, this is the so-called. signal-to-noise ratio.
SOI
Nonlinear distortions (ND) of UMZCH are components of the output signal spectrum that were not present in the input signal. Theoretically, it is best to “push” the NI under the level of its own noise, but technically this is very difficult to implement. In practice, they take into account the so-called. masking effect: at volume levels below approx. At 30 dB, the range of frequencies perceived by the human ear narrows, as does the ability to distinguish sounds by frequency. Musicians hear notes, but find it difficult to assess the timbre of the sound. In people without a hearing for music, the masking effect is observed already at 45-40 dB of volume. Therefore, an UMZCH with a THD of 0.1% (–60 dB from a volume level of 110 dB) will be assessed as Hi-Fi by the average listener, and with a THD of 0.01% (–80 dB) can be considered not distorting the sound.
Lamps
The last statement will probably cause rejection, even fury, among adherents of tube circuitry: they say, real sound is produced only by tubes, and not just some, but certain types of octal ones. Calm down, gentlemen - the special tube sound is not a fiction. The reason is the fundamentally different distortion spectra of electronic tubes and transistors. Which, in turn, are due to the fact that in the lamp the flow of electrons moves in a vacuum and quantum effects do not appear in it. A transistor is a quantum device, where minority charge carriers (electrons and holes) move in the crystal, which is completely impossible without quantum effects. Therefore, the spectrum of tube distortions is short and clean: only harmonics up to the 3rd - 4th are clearly visible in it, and there are very few combinational components (sums and differences in the frequencies of the input signal and their harmonics). Therefore, in the days of vacuum circuitry, SOI was called harmonic distortion (CHD). In transistors, the spectrum of distortions (if they are measurable, the reservation is random, see below) can be traced up to the 15th and higher components, and there are more than enough combination frequencies in it.
At the beginning of solid-state electronics, designers of transistor UMZCHs used the usual “tube” SOI of 1-2% for them; Sound with a tube distortion spectrum of this magnitude is perceived by ordinary listeners as pure. By the way, the very concept of Hi-Fi did not yet exist. It turned out that they sound dull and dull. In the process of developing transistor technology, an understanding of what Hi-Fi is and what is needed for it was developed.
Currently, the growing pains of transistor technology have been successfully overcome and side frequencies at the output of a good UMZCH are difficult to detect using special measurement methods. And lamp circuitry can be considered to have become an art. Its basis can be anything, why can’t electronics go there? An analogy with photography would be appropriate here. No one can deny that a modern digital SLR camera produces an image that is immeasurably clearer, more detailed, and deeper in the range of brightness and color than a plywood box with an accordion. But someone, with the coolest Nikon, “clicks pictures” like “this is my fat cat, he got drunk like a bastard and is sleeping with his paws outstretched,” and someone, using Smena-8M, uses Svemov’s b/w film to take a picture in front of which there is a crowd of people at a prestigious exhibition.
Note: and calm down again - not everything is so bad. Today, low-power lamp UMZCHs have at least one application left, and not the least important, for which they are technically necessary.
Experimental stand
Many audio lovers, having barely learned to solder, immediately “go into tubes.” This in no way deserves censure, on the contrary. Interest in the origins is always justified and useful, and electronics has become so with tubes. The first computers were tube-based, and the on-board electronic equipment of the first spacecraft was also tube-based: there were already transistors then, but they could not withstand extraterrestrial radiation. By the way, at that time lamp microcircuits were also created under the strictest secrecy! On microlamps with a cold cathode. The only known mention of them in open sources is in the rare book by Mitrofanov and Pickersgil “Modern receiving and amplifying tubes”.
But enough of the lyrics, let's get to the point. For those who like to tinker with the lamps in Fig. – diagram of a bench lamp UMZCH, intended specifically for experiments: SA1 switches the operating mode of the output lamp, and SA2 switches the supply voltage. The circuit is well known in the Russian Federation, a minor modification affected only the output transformer: now you can not only “drive” the native 6P7S in different modes, but also select the screen grid switching factor for other lamps in ultra-linear mode; for the vast majority of output pentodes and beam tetrodes it is either 0.22-0.25 or 0.42-0.45. For the manufacture of the output transformer, see below.
Guitarists and rockers
This is the very case when you can’t do without lamps. As you know, the electric guitar became a full-fledged solo instrument after the pre-amplified signal from the pickup began to be passed through a special attachment - a fuser - which deliberately distorted its spectrum. Without this, the sound of the string was too sharp and short, because the electromagnetic pickup reacts only to the modes of its mechanical vibrations in the plane of the instrument soundboard.
An unpleasant circumstance soon emerged: the sound of an electric guitar with a fuser acquires full strength and brightness only at high volumes. This is especially true for guitars with a humbucker-type pickup, which gives the most “angry” sound. But what about a beginner who is forced to rehearse at home? You can’t go to the hall to perform without knowing exactly how the instrument will sound there. And rock fans just want to listen to their favorite things in full juice, and rockers are generally decent and non-conflict people. At least those who are interested in rock music, and not shocking surroundings.
So, it turned out that the fatal sound appears at volume levels acceptable for residential premises, if the UMZCH is tube-based. The reason is the specific interaction of the signal spectrum from the fuser with the pure and short spectrum of tube harmonics. Here again an analogy is appropriate: a b/w photo can be much more expressive than a color one, because leaves only the outline and light for viewing.
Those who need a tube amplifier not for experiments, but due to technical necessity, do not have time to master the intricacies of tube electronics for a long time, they are passionate about something else. In this case, it is better to make the UMZCH transformerless. More precisely, with a single-ended matching output transformer that operates without constant magnetization. This approach greatly simplifies and speeds up the production of the most complex and critical component of a lamp UMZCH.
“Transformerless” tube output stage of the UMZCH and pre-amplifiers for it
On the right in Fig. a diagram of a transformerless output stage of a tube UMZCH is given, and on the left are pre-amplifier options for it. At the top - with a tone control according to the classic Baxandal scheme, which provides fairly deep adjustment, but introduces slight phase distortion into the signal, which can be significant when the UMZCH is operating on a 2-way speaker. Below is a preamplifier with simpler tone control that does not distort the signal.
But let's get back to the end. In a number of foreign sources, this scheme is considered a revelation, but an identical one, with the exception of the capacitance of the electrolytic capacitors, is found in the Soviet “Radio Amateur Handbook” of 1966. A thick book of 1060 pages. There was no Internet and disk-based databases back then.
In the same place, on the right in the figure, the disadvantages of this scheme are briefly but clearly described. An improved one, from the same source, is given on the trail. rice. right. In it, the screen grid L2 is powered from the midpoint of the anode rectifier (the anode winding of the power transformer is symmetrical), and the screen grid L1 is powered through the load. If, instead of high-impedance speakers, you turn on a matching transformer with regular speakers, as in the previous one. circuit, the output power is approx. 12 W, because the active resistance of the primary winding of the transformer is much less than 800 Ohms. SOI of this final stage with transformer output - approx. 0.5%
How to make a transformer?
The main enemies of the quality of a powerful signal low-frequency (sound) transformer are the magnetic leakage field, the lines of force of which are closed, bypassing the magnetic circuit (core), eddy currents in the magnetic circuit (Foucault currents) and, to a lesser extent, magnetostriction in the core. Because of this phenomenon, a carelessly assembled transformer “sings,” hums, or beeps. Foucault currents are combated by reducing the thickness of the magnetic circuit plates and additionally insulating them with varnish during assembly. For output transformers, the optimal plate thickness is 0.15 mm, the maximum allowable is 0.25 mm. You should not take thinner plates for the output transformer: the fill factor of the core (the central core of the magnetic circuit) with steel will fall, the cross-section of the magnetic circuit will have to be increased to obtain a given power, which will only increase distortions and losses in it.
In the core of an audio transformer operating with permanent magnetization (for example, the anode current of a single-ended output stage) there must be a small (determined by calculation) non-magnetic gap. The presence of a non-magnetic gap, on the one hand, reduces signal distortion from constant magnetization; on the other hand, in a conventional magnetic circuit it increases the stray field and requires a core with a larger cross-section. Therefore, the non-magnetic gap must be calculated at the optimum and performed as accurately as possible.
For transformers operating with magnetization, the optimal type of core is made of Shp (cut) plates, pos. 1 in Fig. In them, a non-magnetic gap is formed during core cutting and is therefore stable; its value is indicated in the passport for the plates or measured with a set of probes. The stray field is minimal, because the side branches through which the magnetic flux is closed are solid. Transformer cores without bias are often assembled from Shp plates, because Shp plates are made from high-quality transformer steel. In this case, the core is assembled across the roof (the plates are laid with a cut in one direction or the other), and its cross-section is increased by 10% compared to the calculated one.
It is better to wind transformers without bias on USH cores (reduced height with widened windows), pos. 2. In them, a decrease in the stray field is achieved by reducing the length of the magnetic path. Since USh plates are more accessible than Shp, transformer cores with magnetization are often made from them. Then the core assembly is carried out cut to pieces: a package of W-plates is assembled, a strip of non-conducting non-magnetic material is placed with a thickness equal to the size of the non-magnetic gap, covered with a yoke from a package of jumpers and pulled together with a clip.
Note:“sound” signal magnetic circuits of the ShLM type are of little use for output transformers of high-quality tube amplifiers; they have a large stray field.
At pos. 3 shows a diagram of the core dimensions for calculating the transformer, at pos. 4 design of the winding frame, and at pos. 5 – patterns of its parts. As for the transformer for the “transformerless” output stage, it is better to make it on the ShLMm across the roof, because the bias is negligible (the bias current is equal to the screen grid current). The main task here is to make the windings as compact as possible in order to reduce the stray field; their active resistance will still be much less than 800 Ohms. The more free space left in the windows, the better the transformer turned out. Therefore, the windings are wound turn to turn (if there is no winding machine, this is a terrible task) from the thinnest possible wire; the laying coefficient of the anode winding for the mechanical calculation of the transformer is taken 0.6. The winding wire is PETV or PEMM, they have an oxygen-free core. There is no need to take PETV-2 or PEMM-2; due to double varnishing, they have an increased outer diameter and a larger scattering field. The primary winding is wound first, because it is its scattering field that most affects the sound.
You need to look for iron for this transformer with holes in the corners of the plates and clamping brackets (see figure on the right), because “for complete happiness,” the magnetic circuit is assembled as follows. order (of course, the windings with leads and external insulation should already be on the frame):
- Prepare acrylic varnish diluted in half or, in the old fashioned way, shellac;
- Plates with jumpers are quickly coated with varnish on one side and placed into the frame as quickly as possible, without pressing too hard. The first plate is placed with the varnished side inward, the next one with the unvarnished side to the first varnished, etc.;
- When the frame window is filled, staples are applied and bolted tightly;
- After 1-3 minutes, when the squeezing of varnish from the gaps apparently stops, add the plates again until the window is filled;
- Repeat paragraphs. 2-4 until the window is tightly packed with steel;
- The core is pulled tightly again and dried on a battery, etc. 3-5 days.
The core assembled using this technology has very good plate insulation and steel filling. Magnetostriction losses are not detected at all. But keep in mind that this technique is not applicable for permalloy cores, because Under strong mechanical influences, the magnetic properties of permalloy irreversibly deteriorate!
On microcircuits
UMZCHs on integrated circuits (ICs) are most often made by those who are satisfied with the sound quality up to average Hi-Fi, but are more attracted by the low cost, speed, ease of assembly and the complete absence of any setup procedures that require special knowledge. Simply, an amplifier on microcircuits is the best option for dummies. The classic of the genre here is the UMZCH on the TDA2004 IC, which has been on the series, God willing, for about 20 years now, on the left in Fig. Power – up to 12 W per channel, supply voltage – 3-18 V unipolar. Radiator area – from 200 sq. see for maximum power. The advantage is the ability to work with a very low-resistance, up to 1.6 Ohm, load, which allows you to extract full power when powered from a 12 V on-board network, and 7-8 W when supplied with a 6-volt power supply, for example, on a motorcycle. However, the output of the TDA2004 in class B is not complementary (on transistors of the same conductivity), so the sound is definitely not Hi-Fi: THD 1%, dynamics 45 dB.
The more modern TDA7261 does not produce better sound, but is more powerful, up to 25 W, because The upper limit of the supply voltage has been increased to 25 V. The lower limit, 4.5 V, still allows it to be powered from a 6 V on-board network, i.e. The TDA7261 can be started from almost all on-board networks, except for the aircraft 27 V. Using attached components (strapping, on the right in the figure), the TDA7261 can operate in mutation mode and with the St-By (Stand By) function, which switches the UMZCH to the minimum power consumption mode when there is no input signal for a certain time. Convenience costs money, so for a stereo you will need a pair of TDA7261 with radiators from 250 sq. see for each.
Note: If you are somehow attracted to amplifiers with the St-By function, keep in mind that you should not expect speakers wider than 66 dB from them.
“Super economical” in terms of power supply TDA7482, on the left in the figure, operating in the so-called. class D. Such UMZCHs are sometimes called digital amplifiers, which is incorrect. For real digitization, level samples are taken from an analog signal with a quantization frequency that is no less than twice the highest of the reproduced frequencies, the value of each sample is recorded in a noise-resistant code and stored for further use. UMZCH class D – pulse. In them, the analogue is directly converted into a sequence of high-frequency pulse-width modulated (PWM), which is fed to the speaker through a low-pass filter (LPF).
Class D sound has nothing in common with Hi-Fi: a SOI of 2% and dynamics of 55 dB for a Class D UMZCH are considered very good indicators. And TDA7482 here, it must be said, is not the optimal choice: other companies specializing in class D produce UMZCH ICs that are cheaper and require less wiring, for example, D-UMZCH of the Paxx series, on the right in Fig.
Among the TDAs, the 4-channel TDA7385 should be noted, see the figure, on which you can assemble a good amplifier for speakers up to medium Hi-Fi, inclusive, with frequency division into 2 bands or for a system with a subwoofer. In both cases, low-pass and mid-high-frequency filtering is done at the input on a weak signal, which simplifies the design of the filters and allows deeper separation of the bands. And if the acoustics are subwoofer, then 2 channels of the TDA7385 can be allocated for a sub-ULF bridge circuit (see below), and the remaining 2 can be used for MF-HF.
UMZCH for subwoofer
A subwoofer, which can be translated as “subwoofer” or, literally, “boomer,” reproduces frequencies up to 150-200 Hz; in this range, human ears are practically unable to determine the direction of the sound source. In speakers with a subwoofer, the “sub-bass” speaker is placed in a separate acoustic design; this is the subwoofer as such. The subwoofer is placed, in principle, as conveniently as possible, and the stereo effect is provided by separate MF-HF channels with their own small-sized speakers, for the acoustic design of which there are no particularly serious requirements. Experts agree that it is better to listen to stereo with full channel separation, but subwoofer systems significantly save money or labor on the bass path and make it easier to place acoustics in small rooms, which is why they are popular among consumers with normal hearing and not particularly demanding ones.
The “leakage” of mid-high frequencies into the subwoofer, and from it into the air, greatly spoils the stereo, but if you sharply “cut off” the sub-bass, which, by the way, is very difficult and expensive, then a very unpleasant sound jumping effect will occur. Therefore, channels in subwoofer systems are filtered twice. At the input, electric filters highlight midrange-high frequencies with bass “tails” that do not overload the midrange-high frequency path, but provide a smooth transition to sub-bass. Bass with midrange “tails” are combined and fed to a separate UMZCH for the subwoofer. The midrange is additionally filtered so that the stereo does not deteriorate; in the subwoofer it is already acoustic: a sub-bass speaker is placed, for example, in the partition between the resonator chambers of the subwoofer, which do not let the midrange out, see on the right in Fig.
A UMZCH for a subwoofer is subject to a number of specific requirements, of which “dummies” consider the most important to be as high a power as possible. This is completely wrong, if, say, the calculation of the acoustics for the room gave a peak power W for one speaker, then the power of the subwoofer needs 0.8 (2W) or 1.6W. For example, if S-30 speakers are suitable for the room, then a subwoofer needs 1.6x30 = 48 W.
It is much more important to ensure the absence of phase and transient distortions: if they occur, there will definitely be a jump in the sound. As for SOI, it is permissible up to 1%. Intrinsic bass distortion of this level is not audible (see curves of equal volume), and the “tails” of their spectrum in the best audible midrange region will not come out of the subwoofer.
To avoid phase and transient distortions, the amplifier for the subwoofer is built according to the so-called. bridge circuit: the outputs of 2 identical UMZCHs are switched on back-to-back through a speaker; signals to the inputs are supplied in antiphase. The absence of phase and transient distortions in the bridge circuit is due to the complete electrical symmetry of the output signal paths. The identity of the amplifiers forming the arms of the bridge is ensured by the use of paired UMZCHs on ICs, made on the same chip; This is perhaps the only case when an amplifier on microcircuits is better than a discrete one.
Note: The power of a bridge UMZCH does not double, as some people think, it is determined by the supply voltage.
An example of a bridge UMZCH circuit for a subwoofer in a room up to 20 sq. m (without input filters) on the TDA2030 IC is given in Fig. left. Additional midrange filtering is carried out by circuits R5C3 and R’5C’3. Radiator area TDA2030 – from 400 sq. see. Bridged UMZCHs with an open output have an unpleasant feature: when the bridge is unbalanced, a constant component appears in the load current, which can damage the speaker, and the sub-bass protection circuits often fail, turning off the speaker when not needed. Therefore, it is better to protect the expensive oak bass head with non-polar batteries of electrolytic capacitors (highlighted in color, and the diagram of one battery is given in the inset.
A little about acoustics
The acoustic design of a subwoofer is a special topic, but since a drawing is given here, explanations are also needed. Case material – MDF 24 mm. The resonator tubes are made of fairly durable, non-ringing plastic, for example, polyethylene. The internal diameter of the pipes is 60 mm, the protrusions inward are 113 mm in the large chamber and 61 in the small chamber. For a specific loudspeaker head, the subwoofer will have to be reconfigured for the best bass and, at the same time, the least impact on the stereo effect. To tune the pipes, they take a pipe that is obviously longer and, by pushing it in and out, achieve the required sound. The protrusions of the pipes outward do not affect the sound; they are then cut off. The pipe settings are interdependent, so you will have to tinker.
Headphone amplifier
A headphone amplifier is most often made by hand for two reasons. The first is for listening “on the go”, i.e. outside the home, when the power of the audio output of the player or smartphone is not enough to drive “buttons” or “burdocks”. The second is for high-end home headphones. A Hi-Fi UMZCH for an ordinary living room is needed with dynamics of up to 70-75 dB, but the dynamic range of the best modern stereo headphones exceeds 100 dB. An amplifier with such dynamics is more expensive than some cars, and its power will be from 200 W per channel, which is too much for an ordinary apartment: listening at a power that is much lower than the rated power spoils the sound, see above. Therefore, it makes sense to make a low-power, but with good dynamics, a separate amplifier specifically for headphones: the prices for household UMZCHs with such an additional weight are clearly absurdly inflated.
The circuit of the simplest headphone amplifier using transistors is given in pos. 1 pic. The sound is only for Chinese “buttons”, it works in class B. It is also no different in terms of efficiency - 13 mm lithium batteries last for 3-4 hours at full volume. At pos. 2 – TDA’s classic for on-the-go headphones. The sound, however, is quite decent, up to average Hi-Fi depending on the track digitization parameters. There are countless amateur improvements to the TDA7050 harness, but no one has yet achieved the transition of sound to the next level of class: the “microphone” itself does not allow it. TDA7057 (item 3) is simply more functional; you can connect the volume control to a regular, not dual, potentiometer.
The UMZCH for headphones on the TDA7350 (item 4) is designed to drive good individual acoustics. It is on this IC that headphone amplifiers in most middle and high-class household UMZCHs are assembled. The UMZCH for headphones on KA2206B (item 5) is already considered professional: its maximum power of 2.3 W is enough to drive such serious isodynamic “mugs” as TDS-7 and TDS-15.
For a snack
In conclusion - a completely exotic headphone amplifier... on tubes, see figure, with only one channel, the other requires the same rarities. Although this amplifier implements almost all tube rituals (except, perhaps, a fixed bias from batteries), it is not only and not so much a tribute to vacuum audiophiles: when listening to the TDS-7 through this amplifier, the sound is through-through analogue, compared to the KA2206B, improves noticeably.
Especially such homemade products, which at first glance may not be easy. In this article I will tell you how to make your own homemade sound amplifier without any difficulties or financial costs.
Many beginners in the radio business know that a sound amplifier, be it in a music center or a radio tape recorder, consists of a main element, such as a microcircuit.
Integrated amplifier chips are widely used in home appliances such as televisions and computer speakers. But the fact is that the amplifier in such cases is weak, and it will cost more, since it is already assembled.
In order to assemble a sound amplifier, which by the way is powered by a 12 V power supply, you need:
Amplifier chip, purchased it at a radio store for 56 rubles
Capacitors, one 2200 µF, the other 100 µF
Fiberglass, a small piece is enough for our microcircuit
Box for the body.
Plug for connecting a tulip
Plug for sound input, from broken headphones or from computer speakers, no matter where from
Switch
Five wires
Cooling radiator
Four screws
Hot melt adhesive
Stationery knife
Soldering iron, for convenience, 20-40 watts
Rosin
Thermal paste
Varnish, solvent, hydrogen peroxide, citric acid, salt.
All the components are ready and they cost no more than 150 rubles in total, since the microcircuit can be pulled out of a TV, which is even less common on the market; an old-style TV will not have such an amplifier.
To begin with, let’s arm ourselves with fiberglass laminate, hydrogen peroxide, citric acid and salt. This entire solution must be mixed in a bowl with a wall height of 10 - 20 mm, mix in the proportion of 50 ml of peroxide per 15 grams of citric acid, add a pinch of salt there, 5 grams is enough.
The next step is to draw out the future paths of the board with nail polish. We do this carefully, wiping off the excess with solvent. Our microcircuit requires this arrangement of tracks.
We wait about 5 minutes and lower the board into the solution; on average, the board should be etched in 30-40 minutes. After time has passed, it is necessary to remove the varnish.
When the varnish has been wiped off (you can use any solvent), you need to check in the light to see if there is any displacement or errors, such as sticking of one leg to another; if there is an error, this can be corrected with a utility knife.
Now the board needs to be covered with a layer of tin, first we coat the tracks with rosin, then we tin all the tracks with a soldering iron. Then we attach the microcircuit and solder it strictly to the legs. The microcircuit cannot be overheated; it may not work.
Next, you can solder the wires, first we solder the sound output, take two wires and solder them to our plug for connecting the tulip. We have one sound output.
After the sound comes out, solder a jumper between leg 4 and 7, this is a minus.
Then we solder a 100 uF capacitor to the third track.
We solder it plus to the track and minus to the other side of the track, as in the photo.
For power supply you need a filter, it will be a 2200 uF capacitor. Solder it to the plus and minus of the power supply.
We solder two wires to the power paths.
The next step is soldering the audio input plug.
At this point, the amplifier is completely ready; before installing it in the case, it is better to check it by first securing it to the radiator. After checking, you can install everything in the case. First, let's cut holes for installing the radiator using a utility knife.
The photo shows that everything fit well. Then you need to secure the radiator with four screws.
When the radiator is firmly seated, you can make holes for connecting to the speaker through the tulip and the power switch. We glue everything with hot glue. Then you can install the amplifier on the radiator using thermal paste.
