Homemade tube amplifier. Toropkin M.V. DIY tube Hi-Fi amplifier (2nd ed.) Circuits of homemade hi-fi amplifiers

It is no secret that tube sound reinforcement equipment has been experiencing a renaissance over the last 10 years, and photographs of tube structures have appeared on the covers of popular audio magazines; The production of radio tubes has been mastered (or resumed?) by leading companies in the USA, Europe and Japan.

Unfortunately, information about radio tubes is scattered across outdated reference books published before the 80s of the last century, which are a bibliographic rarity, as well as on Internet sites that are often not optimized for search engines. There is also a lack of information on the sound use of lamps that were not originally intended for these purposes (modulator, generator, television).

The purpose of the book is to bring together information about the most popular radio tubes designed (or used) for use in sound reinforcement and to introduce the reader to modern tube circuitry.
Not only data on pinouts is provided, electrical parameters, current-voltage characteristics (volt-ampere characteristics) of radio tubes, but also recommendations for their use, including various schemes for constructing tube stages and sound amplification equipment.
The author deliberately avoids subjective assessments of sound quality, pseudoscientific, overtly commercial and even mystical terms (“virtual depth”, “tonal balance”, “airiness”, etc.). The reasons why one amplifier provides better sound than another (having similar objective parameters) should be sought with the help of a spectrum analyzer, and not with magical passes and spells.

The book is addressed to lovers of high-quality sound reproduction. This material will explain how to assemble your first Hi-Fi tube amplifier. But that's not all that this book is interesting about.

For beginning radio amateurs, the chapter “Basics of circuit design of tube amplifier stages” is presented. Those who have decided to purchase a ready-made amplifier or compare the characteristics of factory-made models will be interested in the chapter “Overview of the market for tube Hi-Fi amplifiers. How to make the right choice when purchasing."

The book is also reference manual on lamp circuitry, electronic tubes, used in modern high-quality sound reinforcement equipment, a guide to the design of amplifier stages with an overview of the most interesting circuit solutions. The appendices provide calculation methods and ready-made examples designs of output transformers. Chapter “Overview of Internet resources on lamp Hi-Fi Amplifier Technology" will significantly expand the reader's horizons in the field of tube circuitry and save time (and money) when searching for information on the Internet.

The book is intended for a wide range of radio amateurs and lovers of high-quality sound.

Attention!
Lamp designs use life-threatening voltages. When working with the diagrams given in this book, be extremely careful and careful. Beginner radio amateurs should check and first turn on the assembled structure under the guidance of experienced specialists. Remember that even a device that is disconnected from the electrical network, - power supply capacitors can retain charge for several days. Take care of yourself and your loved ones.

Publisher: Science and Technology
Series: Home Master
Year: 2006
Pages: 272
ISBN: 5-94387-177-2
Format: PDF
Quality: excellent
File size: 67.28 MB
Download: Toropkin M.V. DIY tube Hi-Fi amplifier (2nd ed.)

The TDA2050, TDA2030 and LM1875 chips are monophonic ULF chips. These microcircuits have good output characteristics, which is why they are widely used in industrial audio systems. Their only difference is the output power and supply voltage rating. All chips are powered from a bipolar source, so the indicated power is purely audio power.

Today we’ll look at a low-frequency HI-FI amplifier circuit based on the LM1875 chip. Experience shows that this microcircuit sounds better than others, although I may be wrong. It costs an order of magnitude more than the TDA2050 chip, I think this is not without reason.

The LM1875 is widely used in 2:1, 3:1 and 5:1 audio systems. You should not raise the input voltage rating more than ±25V, although the circuit works normally with a ±25V power supply. This chip can be used to build a high-quality class AB amplifier. This amplifier belongs to the HI-FI category and develops an output power of about 20 watts. output power can reach up to 30 watts (if you increase the supply voltage), but after 20 watts the harmonic distortion increases sharply.

Hi fi amplifier circuit

So, to assemble a HI-FI amplifier with your own hands, you will need to find necessary components. Any network transformer with a power of more than 40 watts is suitable as a supply transformer. For filters, you need to use electrolytic capacitors with a voltage of at least 35 Volts; you need to take a larger capacitance (2200 μF or more). In my case, the amplifier is powered by a toroidal transformer with a power of 100 watts, 20 volts on the shoulder - this is the nominal supply voltage for this microcircuit.

The heat sink plays an important role; it is advisable to strengthen the microcircuit onto the heat sink by applying thermal paste in advance. There are two main options for amplifying a circuit - a bridge circuit using two microcircuits and amplification using an additional output stage, but we'll talk about that another time.

This article is about how to assemble an amplifier for 3,000 rubles that combines the best qualities of these two beauties in the photo below...

Of course you recognized them...
More recently, I had two of the most prominent representatives of Soviet amplifier construction - Odyssey U-010 stereo Hi-Fi from 1987 and Brig-001 from 1983.

And two more less bright, but more common - Amfiton 202 and Electronics 50U-017, which are also presented in the pictures below.

Plus, there were Odyssey 001, Rostov MK-105S, TDA 2004, TDA2030A, TDA2050, TDA7294, all included as standard.

Now I no longer have any of this...
But there is this article in which I will tell you why. First things first, the most interesting stuff is usually at the end.

Over the course of a year in my city, I bought more or less working Soviet amplifiers, restored them and listened to them, hoping to find one that would satisfy me with sound quality, assembly, design, and I simply liked it, and I describe the results of my searches in this article.

So...
- old, manufactured in ’75, but this grandfather knocks 30GD out of the basket like it’s not 30 watts / 4 ohms according to the passport, but all 100, seriously, I was stunned by what he does with the low-frequency driver, and this is probably the only thing I care about he liked it, but no, there is something else - he is 37 years old and he works!!! The distortion factor is 1% and it is noticeable, although the sound is not soapy - there are so many highs that you can pull out the high-frequency speakers with such an amplifier, and the bass is quite unique due to germanium transistors. Paired with the S30B, it definitely plays better than budget Svens, and besides, it is truly retro in wood and with good assembly. I liked it.

Rostov MK-105 S- this is a tape recorder, the power for the S90 is just right, it was supplied with them, the sound is very good, and with these speakers, soft bass, good design, beautiful dial indicators, but even when replacing all the capacitors, hissing remains, this is due with a long journey sound signal to the power amplifier (via the input amplifier, tone control, playback amplifier), in addition, the signal circuits are not shielded, but if you turn up the volume this drawback is no longer audible. I liked it.

Amphiton 50U-202- probably like any similar amphiton model range(25U, 35U) is not suitable for high-quality sound reproduction, no matter what you do with it, there are no highs, or if you turn it up, they are distorted, instead of bass there is hum, and if you turn on loudness compensation, then the active subwoofer filter is ready)). The device is distinguished by its simplicity and reliability, even excessive, probably many users of this amplifier have ever had the thought of replacing one resistor in the protection in order to reduce sensitivity. It is of interest only as a case with good radiators for installing TDAs, for example. Didn't like it.

Electronics 50U-017. Electronics, as the flagship of Soviet electronics, loved to make watches and calculators, so they would continue to do so... I have never seen such sophisticated circuitry, it feels like they crammed everything they could into it, as if they hadn’t installed a processor yet)), but somehow the sound is positive this had no effect, noisy, incorrect due to the electronic switch and the same unshielded long signal loops as in Rostov 105, the tone controls are too sharp, with increasing power the distortion increases too much, but the loudness compensation is unusual, as if pressing, deep, and a nice indicator, however The main thing is the sound, but it’s not very good. Didn't like it.

TDA 2004- if only it were...

TDA2030A– well, so-so, but you can fry something or someone on its radiator)).

TDA2050– that’s already something, I overclocked it to 50 Watts/4 Ohms, it held up, the sound is pretty good if you don’t listen too closely, because... The detailing is typical microcircuit, i.e. soap, but I liked its soft bass tonality and reliability. In my optimal choice in order to listen to music without bothering and at no extra cost. There was an idea to make active S30s with it, I think they would work well together. I liked it.

TDA7294– I won’t write much, everyone knows everything, the microcircuit is very popular. I liked it because of the price/quality ratio, probably only the LM3886 is better in sound, but at least in our country it is twice as expensive. The detail is higher than that of the TDA2050 and in comparison with it the sound is colder and sharper, perhaps due to more pronounced high frequencies. Although, if you don’t find fault, the TDA7294 is quite suitable for the S90 as an amplifier for listening to pop music at an RMS power of up to 50 Watts, higher than that it’s no longer hi-fi... Until I bought the Odyssey-010 it seemed okay, now I can’t perceive it well.

Before moving on to the best ones, a few words about how I listened. Used for listening sound card HD Audio, bitrate from 320 and music of different styles, here are just some of the compositions:
Dj Matisse & Lounge Paradise - This Love (Maroon 5 Cover);
DJ Shah feat. Nadja Nooijen – Over and Over (Original Vesrion);
Lesopoval – Ya kuplu tebe dom;
Wicked DJs - Disco Rocker (Picker Remix);
Stas Mihaylov – Koroleva;
Tritonal Ft. Cristina Soto - Forgive Me, Forget You (Triple Mash Intro);
Eva Polna – Luby menya po francuzski (Fonzarelli Chill Out Acoustic Mix);
Dire Straits - Money For Nothing (Album Version).

The speakers are my favorite S90, which I naturally modified; the essence of the modification should probably be entered as a standard in the GOST register, but I will once again list the main treatment methods:

• Coating seams with sealant
• Treatment of the internal surface with rubber-bitumen mastic
• Pasting the inner surface with synthetic padding (ideally, of course, with felt, but I just couldn’t find it anywhere in the city, and I don’t want to cut felt boots, and I can’t get by with just one pair)
• Damping the mid-frequency speaker or replacing it with 6gdsh - by the way, I didn’t find that either, so I sealed the basket windows with 15gdsh foam
• Replaced the wires with thicker ones
• I painted the grilles with glossy black enamel and covered them with wood-effect self-adhesive
• I laid a couple of bags of cotton wool
• I want to put them on tenons, but I don’t have time to sharpen everything, and I think this will be the final point of improvement, I can’t get more out of them.

And now they really sound!!!
And now about the best.

Odyssey U-010 stereo Hi-Fi– brutal, quite a solid thing, 16 kilograms of non-ferrous metal.
In addition to its attractive appearance, it has two advantages - power and bass. If you measure root mean square power according to the RMS standard, then at 4 Ohms I squeezed out 183 Watts, at 8 Ohms 120 Watts, beast)). Probably everyone has had this feeling when you are driving our domestic car and accelerate to a hundred and then slow down, because... it seems like it’s about to fall apart, and then you get into a foreign car, you give it a little gas, and it’s already 60, a little more 100, but everything is comfortable and the speed is not noticeable, it’s about the same here, I crank it up to full, so that sound wave the bass moves the T-shirt, but the sound is not distorted, it is almost the same as when the volume knob is on two, although the power for the speakers is already dangerous, the music does not turn into a coherent set of sounds, well, except at the very maximum, I really like it.

By the way, by the way, you can also say about it “a bucket with nuts.” The parts are random, the wires of the power supply and output transistors are thin, there is no shielding, the soldering and PCB, to put it mildly, are not the best, while I was resoldering the capacitors, several tracks came off, I had to lay the wires.

A preamplifier for a device of this level is terrible, when all the knobs are at zero we already hear a slightly different sound and only by connecting the signal directly to the PA plug can we talk about quality, although this preamplifier is interesting with such a unique thing as “frequency response balance”, discrete controls and many functional buttons .

The power supply is great! Although the transformer is humming, I filled it with paraffin - it didn’t help, but it’s so powerful and tightly assembled. Distinctive feature This amplifier has a voltage stabilizer, which is generally a unique thing in Soviet amplifiers, as is the balance of the frequency response. The stabilizer allows you to maintain a constant voltage level on the power amplifier +/- 37 Volts even at high volumes. The voltage drop, according to my measurements, was only 0.6 Volts! This largely explains the good sound quality at high powers.

The protection allows you to work not only with an 8-ohm load, but with a 4-ohm load, however, at a volume of more than half you need to be careful, when the output is shorted, the protection does not help, AND YOU DO NOT NEED TO CHECK FOR ME!, although on the other side they fly out for some reason - then transistors like KT502 are in the stabilizer, and a couple of KT818/819 outputs in the PA remain unbroken, strange.

Despite the shortcomings of the performance, of course, it is worth noting the sound, it is good, or rather the bass - it is clear, even a little rough, but quite deep. I love progressive house, tech, electro - it’s great for such styles, which can’t be said about pop and classical, it doesn’t have enough highs by default (the initial problem is in the tone block), you have to turn them all the way up by hand, then the cymbals can be heard well, the mids so himself and in this he will clearly lose to the next one.

Brig 001– a copy of 1983, the second version of the circuit design with one op-amp in the power amplifier. I read somewhere that the first copies were installed on personal orders in the offices of officials of the CPSU Central Committee, who loved good sound and who then listened exclusively to Japanese Marants and Technixes, which were naturally not available to ordinary citizens. However, the brig was not available to everyone, since its price at that time was about 600 rubles, while the same Odyssey -010 later cost 350.

Of course, the brig is the best, the best of the Soviet ones of that time, there is a lot of controversy and discussion around it, but few improvements, this means that for some it is already not bad, but not for me. It is undoubtedly very reliable and stable, and also well assembled, I had a copy with military acceptance parts. In general, it is not particularly repairable due to the fact that all the main components are connected not using plugs and plugs, but with wires and soldering, however, unscrewing any board is not particularly difficult, but to remove it you will have to solder. The quality of PCB and soldering is excellent. The number of electrolytic capacitors is probably even smaller than in all amplifiers described earlier.

About sound. This is an amplifier for chanson. And restaurant music, which I also love, it’s a great pleasure to listen to it, in general, everything with vocals and live instruments, classics, jazz. Sparkling highs, good mids, vocals and good lows, judging from this sequence it is easy to conclude that this is the opposite of Odyssey 010, plus I would add to this statement that listening to the brig through a plug, bypassing the preamplifier, I would not say that it impressed me , rather, on the contrary, the beauty of sound emanating from the brig is largely due to its timbre block.

Many people like its soft bass, personally I don’t, because when listening to electronic or heavier music at rated power, all that soft bass becomes mush.

It turns out that each amplifier is good in its own way, there is no universal one...

Of course, after reviewing all the options, only the last two remain, but they are not alike, heaven and earth, double bass or cymbals, bottom or top, choose who you like. We are all different and the technology is different, some have hearing, some don’t, some can listen to a Chinese radio at the dacha without worrying, while others are not satisfied with the home hi-fi system for a round sum and want something more, people begin to switch to lamps...or spend a lot of money on branded audio equipment. And probably for the average listener, happiness lies in the balance of price and quality, so as for the sound of Soviet amplifiers, it is not bad, after replacing the capacitors, correct ground wiring and shielding, adjusting the quiescent current, replacing some parts with imported ones, increasing the power of the supply transformers or replacing them toroidal...etc., so many things!

I want the bass of the Odyssey and the vocals of the brig, combining best qualities in one device. Do you really need to take and solder one to the other? What should a person do who wants to immerse himself in the world of good sound without much hassle and expense?

My answer is to accumulate the same collection, bring them to mind, listen to them again, make sure that there are no ideal Soviet amplifiers, just as there are no ideal women, be disappointed and sell everything!

And assemble it yourself!

And in a hardware store you always pass with a smile people who choose a beautiful Chinese stupid box with an incredible number of tulips on the back panel and a price equal to their salary... when, right at home, there is an amplifier that is amazing in sound, simplicity and cost, capable of both characteristics and sound make the Chinese receiver smoke! I offer an amplifier that has both high and low, in which everyone will definitely find a part of the brig and the odyssey for themselves and hear for themselves what they want, as I did!

What kind of amplifier is this?

Is this Radiotekhnika U-101?!

In general, Radio Engineering was probably simply created so that one day it would be “raped”... it is beautiful, even now its ergonomics and design excite the inquisitive minds of radio amateurs whose hands are itching and it only has 20 watts - this is too little to resist. We will take it as a very convenient platform for implementing our own ideas in the field of good sound for the home.

From many different schemes, I chose those in this moment, in my personal opinion, are optimal in terms of price/quality ratio, I will say right away that there are no changes other than those described in original diagrams I didn’t contribute, everything was done as it is. I won’t talk for a long time about the blocks themselves, I’m not a radio engineer to explain where things are happening, I’m an ordinary radio amateur, so detailed information read the links provided. I am in no way copying circuits, nor am I encroaching on the copyrights of people - radio engineers who spent time and money creating these circuits. This is a collection, a collection that is quite enough to satisfy the average listener who does not want to pay crazy money for who knows what. This amp really plays!

So, let's begin.

When I finally got under its cover... I was horrified, the wires from the trance were charred, the parts in the power amplifier were soldered in an unclear way, some were soldered in with only one leg, when turned on, the rectifier diodes got very hot and smelled of smoked resistors)). The indicator did not light up. But outwardly it was well preserved. A wonderful example - just what I wanted for a remodel.

Complete dismantling began, as a result of which I left the transformer, tone control, indicator, and input switch.

Photo of the insides (this is not my copy, everything is still good here).

We need it so that there is no hole on the back panel and so that there is a socket for entry. The socket above which “record” is written is free and there are no tracks on the board going to it; we solder a shielded acoustic wire leading to the preamplifier to this socket. This will be the line input. We immediately connect the mass with wiring to the amplifier housing; for this purpose, there are special petals on the frame; if this is not done, there will be noise.

Also, the switch board can serve as a platform for mounting the protection board; to do this, we take out the phono preamplifier box, thereby freeing up space and install the speaker shutdown relay, which is part of the protection circuit, on liquid nails, and mount the board itself next to it.

For example, I managed to clamp the heatsink of the output transistor of the protection circuit between the blades of the fuse socket.

We change electrolytic capacitors. Let's tidy up the wires.

Because I pulled everything out and had to figure out which wire goes where.

If you look at the XP7 socket, the one that is inserted onto the display board, then contacts 10,11,12 go to the filament and are soldered to the corresponding terminals on the transformer.

Contacts 5-plus power, 6-minus power, 4-common are connected to the preamplifier power supply before the stabilizers, it will be shown below how.

Pins 2 and 3 are connected to the outputs of the right and left channel power amplifiers.

To power the power amplifier, I took a toroidal transformer with two identical secondary windings of 20 Volts each with a power of about 100 Watts and bolted it to a metal substrate at the bottom of the amplifier housing, having previously drilled a hole of the required diameter in it. Next to this trance we place the power amplifier rectifier. As a diode bridge, we take an imported KVRS 5010. We assemble a block of 6 capacitors of 4700 μF x 50V, 3 per arm, and shunt it with two 1 μF film capacitors. The scheme is standard and does not need explanation.

The preamplifier, indicator, protection and switching will work from the native trance.
On the original transformer, pin 6 is the middle point, and a voltage of 16.3 V comes out from pins 5 and 5; we connect these contacts with wires to the stabilizer circuit (pins 5-6-5).
And they also provide power for the indicator.

To power the protection circuit we make a separate rectifier, because When connected to an existing preamplifier power supply, noise and low frequency hum, which I could not overcome even with a 10,000 uF capacitor. But here another problem arose - the protection circuit works with a voltage of about 24 Volts, which means that about 16 Volts must be removed from the transformer before the rectifier, however, when measuring the voltages of the remaining windings of the original transformer, the minimum that I found was 37 Volts between terminals 4 and 4', I had to and use them, because a third transformer would be too much. After the rectifier, the voltage was reduced by a chain of a 5-watt 1-kohm resistor and 3 D814 zener diodes connected in series. Of course, it was possible to do everything more professionally and choose a suitable stabilizer, but everything works that way.

This protection circuit is quite popular, so I find it difficult to indicate the original source; a similar circuit is in the brig001 amplifier from the very first edition. One thing I can say is that before this I assembled two more similar circuits, but designed for bipolar power supply and was dissatisfied with their work, the problem was that no matter how I configured and selected the ratings of the parts, the voltage at the contacts of the relay coil did not drop to that level in which the contacts connected to the speaker would open, but here everything is simple and reliable. Turn-on delay is about 2 seconds. During the preliminary check, I connected two AA batteries between the common wire and resistor R1, thereby making sure that even at three volts of DC voltage the circuit works, clicks the relay and turns off the acoustics. Switch S1 is placed on the front panel (mine is to the right of the indicator), it can also control turning off the speakers. Any transistor VT3 that is more powerful from the KT 815, KT 940 series, etc. It gets hot, we put it on the radiator. The board was not created for.

Preamplifier

I wanted to keep my original one, I have it with a version on three microcircuits, but the SP-3 resistor with loudness wore out all my nerves with uneven regulation and rustling, although after filling it with machine oil the situation improved, you need to understand that this is still an emergency measure, but to find one a new one is probably no longer possible even at the manufacturing plant itself, as well as the plant itself...

In addition, the level of noise and distortion of the native tone block was high; I connected it, as many advise, bypassing the first microcircuit and still threw it away. Although as for the sound, I liked this pred, the bass is deep, there are highs and in general it sounds somehow pleasant. However, we are assembling real Hi-Fi and therefore we don’t need any artificially created amenities; we need a tone block that, by default, does not introduce audible changes in the sound.

I once assembled it on a TDA1524 - horror, the distortion coefficient is about 0.3%, that’s a lot, no matter how I didn’t center the resistors or select the capacitors - the microcircuit still makes changes to the sound, it will only work as an active filter for the subwoofer.

I read about Solntsev’s pred, which, in addition to good characteristics, has the same good feedback, but did not collect it, because... there is a need to use a resistor with loudness compensation, which cannot be found in a normal state, and besides, the preamplifier is built on the same Soviet element base, from which I have already moved away to imports.

I assembled it on LM1036 - all the same problems as with TDA, but the distortion coefficient, according to some sources, is about 0.05%, this is already better, and it sounds much better, although cheaper than TDA and still not the same, not Hi- Fi.

And then I assembled a preamplifier using three NE5532 op-amps - class, when the knobs are in the center, it’s as if there was no tone block at all - this is what I wanted and was looking for! For some reason I didn’t find a mode of linearity of the frequency response, harmonic coefficient for these datasheets in the datasheet, but there is data that is 0.007%. It’s bad that there is no loudness compensation and its implementation is possible, again, with a special resistor. This is exactly the tone block that will go into my complete amplifier. This diagram was taken from a foreign site at this link.

I don't think there's much to explain here

I couldn’t find the board online, so I had to develop it myself. The board was not created for laser-iron technology; I make boards the old fashioned way with a marker and etching in ferric chloride.

Amplifier

But here it is, the hero of the occasion, which captivated me with its sound and cost, the power amplifier

I won’t write anything here, probably no one can talk about it better than its creator, whose article you can read

On my own behalf, I’ll just add that at a voltage of +/- 27 Volts, the rms power when supplying a sinusoid with a frequency of 1 kHz at a 4-ohm load was 104 Watts and also - I haven’t heard anything better yet...

About the assembly

In the Radiotekhnika amplifier, the tone block resistors were soldered into the preamplifier board itself and fastened with nuts to the bar, which in turn was connected to the housing. To install imported resistors into the same holes in this strip, you need to drill holes for the resistor protrusion with a diameter of 3 mm as in the pictures. This will provide a guarantee against rotation, besides, this protrusion is formally the middle of the resistor horseshoe, so it is necessary to drill holes as evenly as possible horizontally. WITH reverse side secure the resistors with nuts.

Disabling the tone block in my preamplifier is done using a relay, which I powered in the same place as the protection board; the tone on/off button is located on the front panel (on my left).

After removing the main internals, I also removed the “input copy” and headphone jacks, leaving holes on the front panel, which is not very nice. In this case, I used Soviet non-polar capacitors of the K50-6 type, wrapped with adhesive tape in one layer, which fit very well into these holes, now it looks more like buttons.

The most difficult part of mounting power amplifiers was installing them on radiators. It was necessary, without bending the legs of the transistors too much, to attach them to the radiator, naturally through a layer of thermal paste and mica or thermal rubber, as in my case. To do this, drill holes between the ribs in pre-marked places. Because I didn’t hit it exactly in the middle - I had to grind down the bolt heads perpendicular to the groove for the screwdriver, which in the end was also the best option, because resting against the rib when tightening the nut from the reverse side, the bolt does not turn.

Do not connect the common wire of the power amplifier power supply to the housing frame directly as a preamplifier! A low-frequency hum appears, which is precisely why the problem with the power supply of the protection remained unresolved, because When connecting the common protection wire to the common wire of the power amplifier, a slight hum also appears. Therefore, the protection circuit currently functions only as a turn-on delay circuit; in this mode there is no unnecessary noise.

As a coil in a power amplifier, a coil from Holton, Radiotekhnika’s own powerhouse, was perfect.
When assembling, do not skimp on insulating tape, flux and solder.

Economy

• Dead radio equipment 150 RUR
• Transformer 2x18 Volt for PA, which is especially nice, produced by our TopTransform plant in Rybinsk 700 RUR
• Diode bridge and power amplifier capacitors 410 r
• Preamplifier for NE5532 530 RUR
• Protection board and relay 130 RUR
• UM stonecold 300 r one channel, i.e. stereo 600 RUR
• Manufacturing of circuit boards - textolite, solder, flux, ferric chloride, drills, felt-tip pens 165 RUR
• Buttons, wires, plugs, capacitors for indicators, etc. 125 RUR

It turns out 2810 rub.

Impression

The first thing that catches your ears is the detail of the sound! A good stereo panorama, but as described by the creator of the stonecold, not into space, but for the listener. Many people complain about the S90 because of its poor midrange, but when playing with this amplifier, this drawback is compensated by a more pronounced midrange and excellent vocal reproduction; the highs are also quite sufficient. As for the bass, everything is fine here too, it is clear, but not harsh.

Here you have Odysseus and Brig, all in Radio Engineering. The radiators of the pre-output transistors are warm, the radiators of the output transistors are cold, that’s how it should be!

The power, as I already said, is 100 watts at 4 ohms, there is no way to measure the distortion coefficient, but I think it is small and if compared with the Soviet ones, then 0.01% or even less, at least at high power it plays even cleaner than the Odyssey 010.

I am very pleased, firstly with the sound, secondly with what I did myself, and thirdly with the price-quality ratio.

To finalize everything written above, I will say that with great enthusiasm throughout the year I have been buying Soviet equipment in search of something that will stand on my windowsill and delight me with its sound, but time does not stand still and if once these things cost decent prices by the standards of the money and were quite satisfied with their quality, now we must admit that our civilian electronics remained somewhere there in 91 and it looks like it’s not sad that it remained there forever... We must pay tribute to all Soviet things, we still use and steal them! Now, when you go to a radio parts store, you can buy a KT3102 from 1987 (there is simply no newer one) or an analogue of the BC546, which is newer, cheaper and of better quality, naturally I will choose the second. And I’ll be honest, I didn’t want to sell the brig, I liked it, it had military-grade details, the build quality and sound were quite high, but when I assembled the stonecold I was finally convinced that the obsolescence of the equipment was not just empty words. I listen to it with the preamp turned off, I don’t need to turn up the bass until the glass rattles, everything is enough for me as is. And what is most important is the presence of a strange feeling that any song probably sounds exactly the way it should sound, perhaps this is High Fidelity!

List of radioelements

Designation	Type	Denomination	Quantity	Note	Shop	My notepad
	Preamplifier
OP1-OP3	Operational amplifier	NE5532	3			To notepad
C101, C201	Capacitor	47nF	2			To notepad
C102, C202	Capacitor	1 nF	2			To notepad
C103, C203	Capacitor	2.2 µF	2			To notepad
R101, R201, R116, R216, R119, R219	Resistor	100 kOhm	6			To notepad
R102, R202, R112, R212	Resistor	1 kOhm	4			To notepad
R103, R203, R104, R204, R107-R109, R207-R209	Resistor	10 kOhm	10			To notepad
R105, R205, R106, R206	Resistor	22 kOhm	4			To notepad
R110, R210, R115, R215	Resistor	100 Ohm	4			To notepad
R111, R211	Resistor	10 ohm	2			To notepad
R113, R213	Resistor	15 kOhm	2			To notepad
R114, R214	Resistor	33 kOhm	2			To notepad
R117, R217, R118, R218	Resistor	4.7 kOhm	4			To notepad
VR1A, VR1B, VR2A, VR2B, VR4A, VR4B	Trimmer resistor	100 kOhm	6			To notepad
VR3	Trimmer resistor	50 kOhm	1			To notepad
	Power amplifier 1 channel
OP1	Operational amplifier	TL071	1			To notepad
VT1	Bipolar transistor	BC546	1			To notepad
VT2	Bipolar transistor	BC556	1			To notepad
VT3	Bipolar transistor	TIP32C	1			To notepad
VT4	Bipolar transistor	TIP31C	1			To notepad
VT5	Bipolar transistor	TIP142	1			To notepad
VT6	Bipolar transistor	TIP147	1			To notepad
VD1, VD2	Rectifier diode	1N4148	2			To notepad
VD3, VD4, VD6, VD7	Rectifier diode	1N4007	4			To notepad
VD11, VD12	Zener diode	1N4742	2			To notepad
L1	Inductor	2 µH	1			To notepad
C1, C4, C6	Capacitor	1 µF	3			To notepad
C2	Capacitor	500...5600 pF	1			To notepad
C3	Capacitor	24 pF	1			To notepad
C5, C7		100 µF	2			To notepad
C8, C10	Capacitor	0.33 µF	2			To notepad
C9, C11	Electrolytic capacitor	220 µF	2			To notepad
C12	Capacitor	150 pF	1			To notepad
R1	Resistor	47 kOhm	1			To notepad
R3	Resistor	200 Ohm	1			To notepad
R5, R6	Resistor	2 kOhm	2			To notepad
R7, R8	Resistor	180 Ohm	2			To notepad
R9	Resistor	39 Ohm	1			To notepad
R10	Resistor	22 Ohm	1			To notepad
R11	Resistor	3.9 kOhm	1			To notepad
R14	Resistor	4.7 kOhm	1

– The neighbor stopped 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 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, half of its value is set in it, and in UMZCH in 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.

There are 2 more tricks in this UMZCH: firstly, in very powerful amplifiers, the drive stage of the powerful output also needs to be cooled, so VT3 is placed on a radiator of 100 kW or more. see. For output VT4 and VT5 radiators from 400 sq.m. are needed. see. Secondly, UMZCHs with bipolar power supply are not balanced at all without load. First one or the other output transistor goes into cutoff, and the associated one goes into saturation. Then, at full supply voltage, current surges during balancing can damage the output transistors. Therefore, for balancing (R6, guessed it?), the amplifier is powered from +/–24 V, and instead of a load, a wirewound resistor of 100...200 Ohms is switched on. By the way, the squiggles in some resistors in the diagram are Roman numerals, indicating their required heat dissipation power.

Note: A power source for this UMZCH needs a power of 600 W or more. Anti-aliasing filter capacitors - from 6800 µF at 160 V. In parallel with the electrolytic capacitors of the IP, 0.01 µF ceramic capacitors are included to prevent self-excitation at ultra audio frequencies ah, capable of instantly burning the output transistors.

On the field workers

On the trail. rice. - another option for a fairly powerful UMZCH (30 W, and with a supply voltage of 35 V - 60 W) on powerful field effect transistors:

The sound from it already meets the requirements for Hi-Fi entry level(if, of course, the UMZCH works according to Acustic systems, AC). Powerful field drivers do not require a lot of power to drive, so there is no pre-power cascade. Even more powerful field-effect transistors do not burn out the speakers in the event of any malfunction - they themselves burn out faster. Also unpleasant, but still cheaper than replacing an expensive loudspeaker bass head (GB). This UMZCH does not require balancing or adjustment in general. As a design for beginners, it has only one drawback: powerful field-effect transistors are much more expensive than bipolar transistors for an amplifier with the same parameters. Requirements for individual entrepreneurs are similar to previous ones. case, but its power is needed from 450 W. Radiators – from 200 sq. cm.

Note: there is no need to build powerful UMZCHs on field-effect transistors for switching power supplies, for example. computer When trying to “drive” them into the active mode required for UMZCH, they either simply burn out, or the sound is weak and “no quality at all.” The same applies to powerful high-voltage bipolar transistors, for example. from line scan of old TVs.

Straight up

If you have already taken the first steps, then it is quite natural to want to build Hi-Fi class UMZCH, without going too deep into the theoretical jungle. To do this, you will have to expand your instrumentation - you need an oscilloscope, an audio frequency generator (AFG) and an AC millivoltmeter with the ability to measure the DC component. It is better to take as a prototype for repetition the E. Gumeli UMZCH, described in detail in Radio No. 1, 1989. To build it, you will need a few inexpensive available components, but the quality meets very high requirements: power up to 60 W, band 20-20,000 Hz, frequency response unevenness 2 dB, coefficient nonlinear distortion(THD) 0.01%, self-noise level –86 dB. However, setting up the Gumeli amplifier is quite difficult; if you can handle it, you can take on any other. However, some of the currently known circumstances greatly simplify the establishment of this UMZCH, see below. Bearing in mind this and the fact that not everyone is able to get into the Radio archives, it would be appropriate to repeat the main points.

Schemes of a simple high-quality UMZCH

The Gumeli UMZCH circuits and specifications for them are shown in the illustration. Radiators of output transistors – from 250 sq. see for UMZCH in Fig. 1 and from 150 sq. see for option according to fig. 3 (original numbering). Transistors of the pre-output stage (KT814/KT815) are installed on radiators bent from 75x35 mm aluminum plates with a thickness of 3 mm. There is no need to replace KT814/KT815 with KT626/KT961; the sound does not noticeably improve, but setup becomes seriously difficult.

This UMZCH is very critical to power supply, installation topology and general, so it needs to be installed in a structurally complete form and only with a standard power source. When trying to power it from a stabilized power supply, the output transistors burn out immediately. Therefore, in Fig. drawings of the original ones are given printed circuit boards and setup instructions. We can add to them that, firstly, if “excitement” is noticeable when you first turn it on, they fight it by changing the inductance L1. Secondly, the leads of parts installed on boards should be no longer than 10 mm. Thirdly, it is extremely undesirable to change the installation topology, but if it is really necessary, there must be a frame shield on the side of the conductors (ground loop, highlighted in color in the figure), and the power supply paths must pass outside it.

Note: gaps in the tracks to which the bases are connected powerful transistors– technological, for setting up, after which they are sealed with drops of solder.

Setting up this UMZCH is greatly simplified, and the risk of encountering “excitement” during use is reduced to zero if:

• Minimize interconnect installation by placing the boards on radiators of powerful transistors.
• Completely abandon the connectors inside, performing all installation only by soldering. Then there will be no need for R12, R13 in a powerful version or R10 R11 in a less powerful version (they are dotted in the diagrams).
• Use oxygen-free copper audio wires of minimum length for internal installation.

If these conditions are met, there are no problems with excitation, and setting up the UMZCH comes down to the routine procedure described in Fig.

Wires for sound

Audio wires are not an idle invention. The need for their use at present is undeniable. In copper with an admixture of oxygen, a thin oxide film is formed on the faces of metal crystallites. Metal oxides are semiconductors and if the current in the wire is weak without a constant component, its shape is distorted. In theory, distortions on myriads of crystallites should compensate each other, but very little (apparently due to quantum uncertainties) remains. Sufficient to be noticed by discerning listeners in the background purest sound modern UMZCH.

Manufacturers and traders shamelessly substitute ordinary electrical copper instead of oxygen-free copper - it is impossible to distinguish one from the other by eye. However, there is an area of ​​application where counterfeiting is not clear: twisted pair cable for computer networks. If you put a grid with long segments on the left, it will either not start at all or will constantly glitch. Momentum dispersion, you know.

The author, when there was just talk about audio wires, realized that, in principle, this was not idle chatter, especially since oxygen-free wires by that time had long been used in special-purpose equipment, with which he was well acquainted by his line of work. Then I took and replaced the standard cord of my TDS-7 headphones with a homemade one made from “vitukha” with flexible multi-core wires. The sound, aurally, has steadily improved for end-to-end analogue tracks, i.e. on the way from the studio microphone to the disc, never digitized. Vinyl recordings made using DMM (Direct Metal Mastering) technology sounded especially bright. After this, the interconnect installation of all home audio was converted to “vitushka”. Then completely random people, indifferent to the music and not notified in advance, began to notice the improvement in sound.

How to make interconnect wires from twisted pair, see next. video.

Video: do-it-yourself twisted pair interconnect wires

Unfortunately, the flexible “vitha” soon disappeared from sale - it did not hold well in the crimped connectors. However, for the information of readers, flexible “military” wire MGTF and MGTFE (shielded) is made only from oxygen-free copper. Fake is impossible, because On ordinary copper, tape fluoroplastic insulation spreads quite quickly. MGTF is now widely available and costs much less than branded audio cables with a guarantee. It has one drawback: it cannot be done in color, but this can be corrected with tags. There are also oxygen-free winding wires, see below.

Theoretical Interlude

As we can see, already in the early stages of mastering audio technology, we had to deal with the concept of Hi-Fi (High Fidelity), high fidelity sound reproduction. Hi-Fi comes in different levels, which are ranked according to the following. main parameters:

1. Reproducible frequency band.
2. Dynamic range - the ratio in decibels (dB) of the maximum (peak) output power to the noise level.
3. Self-noise level in dB.
4. Nonlinear distortion factor (THD) at rated (long-term) output power. The SOI at peak power is assumed to be 1% or 2% depending on the measurement technique.
5. Unevenness of the amplitude-frequency response (AFC) in the reproducible frequency band. For speakers - separately at low (LF, 20-300 Hz), medium (MF, 300-5000 Hz) and high (HF, 5000-20,000 Hz) sound frequencies.

Note: the ratio of absolute levels of any values ​​of I in (dB) is defined as P(dB) = 20log(I1/I2). If I1

You need to know all the subtleties and nuances of Hi-Fi when designing and building speakers, and as for a homemade Hi-Fi UMZCH for the home, before moving on to these, you need to clearly understand the requirements for their power required to sound a given room, dynamic range (dynamics), noise level and SOI. It is not very difficult to achieve a frequency band of 20-20,000 Hz from the UMZCH with a roll off at the edges of 3 dB and an uneven frequency response in the midrange of 2 dB on a modern element base.

Volume

The power of the UMZCH is not an end in itself; it must provide the optimal volume of sound reproduction in a given room. It can be determined by curves of equal loudness, see fig. There are no natural noises in residential areas quieter than 20 dB; 20 dB is the wilderness in complete calm. A volume level of 20 dB relative to the threshold of audibility is the threshold of intelligibility - a whisper can still be heard, but music is perceived only as the fact of its presence. An experienced musician can tell which instrument is being played, but not what exactly.

40 dB - the normal noise of a well-insulated city apartment in a quiet area or a country house - represents the intelligibility threshold. Music from the threshold of intelligibility to the threshold of intelligibility can be listened to with deep frequency response correction, primarily in the bass. To do this, the MUTE function (mute, mutation, not mutation!) is introduced into modern UMZCHs, including, respectively. correction circuits in UMZCH.

90 dB is the volume level of a symphony orchestra in a very good concert hall. 110 dB can be produced by an extended orchestra in a hall with unique acoustics, of which there are no more than 10 in the world, this is the threshold of perception: louder sounds are still perceived as distinguishable in meaning with an effort of will, but already annoying noise. The volume zone in residential premises of 20-110 dB constitutes the zone of complete audibility, and 40-90 dB is the zone of best audibility, in which untrained and inexperienced listeners fully perceive the meaning of the sound. If, of course, he is in it.

Power

Calculating the power of equipment at a given volume in the listening area is perhaps the main and most difficult task of electroacoustics. For yourself, in conditions it is better to go from acoustic systems (AS): calculate their power using a simplified method, and take the nominal (long-term) power of the UMZCH equal to the peak (musical) speaker. In this case, the UMZCH will not noticeably add its distortions to those of the speakers; they are already the main source of nonlinearity in the audio path. But the UMZCH should not be made too powerful: in this case, the level of its own noise may be higher than the threshold of audibility, because It is calculated based on the voltage level of the output signal at maximum power. If we consider it very simply, then for a room in an ordinary apartment or house and speakers with normal characteristic sensitivity (sound output) we can take the trace. UMZCH optimal power values:

• Up to 8 sq. m – 15-20 W.
• 8-12 sq. m – 20-30 W.
• 12-26 sq. m – 30-50 W.
• 26-50 sq. m – 50-60 W.
• 50-70 sq. m – 60-100 W.
• 70-100 sq. m – 100-150 W.
• 100-120 sq. m – 150-200 W.
• More than 120 sq. m – determined by calculation based on on-site acoustic measurements.

Dynamics

The dynamic range of the UMZCH is determined by curves of equal loudness and threshold values ​​for different degrees of perception:

1. 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.
2. Other serious music genres – 75 dB excellent, 80 dB “through the roof”.
3. 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 (CH). 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. on 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 rod 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 constant bias (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):

1. Prepare acrylic varnish diluted in half or, in the old fashioned way, shellac;
2. 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.;
3. When the frame window is filled, staples are applied and bolted tightly;
4. After 1-3 minutes, when the squeezing of varnish from the gaps apparently stops, add plates again until the window is filled;
5. Repeat paragraphs. 2-4 until the window is tightly packed with steel;
6. 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: SOI of 2% and dynamics of 55 dB for 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 the 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 costs more 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.

Tube or? At the end of the last century, this issue was often discussed in various “audiophile” publications. Currently, it is, in fact, no longer relevant, since both options are in demand on the market and firmly occupy their places in various “niches” of audio engineering.

High-quality Hi-Fi tube amplifier

For example, for a home audio system, among the modern High End stereo amplifiers, the Houston Mini-1998SE is offered, assembled using 12AX7 and EL84 tubes using a push-pull ultra-linear circuit with a transformer. Despite the limited output power (about 10 W per channel), the sound quality and dynamics of the amplifier with various acoustics, according to experts, is not inferior to high-quality transistor ultrasonics, which develop much greater power.

Interest in Hi-Fi tube amplifiers is currently caused not only by audiophiles’ nostalgia for some special “transparent”, “soft”, “tube” sound, but also by the real advantages of tube ultrasonic frequencies. For practical purposes, the choice is most often made based on the actual capabilities of the amplifier that meets specific requirements.

For example, the construction and operation of a high-quality tube amplifier with a single-ended output stage operating in class “A” mode is in many cases not justified by all indicators, including economic ones. Therefore, many audiophiles and musicians still prefer the classic push-pull tube output stage with a transformer, which, in fact, is the most important element that determines the parameters and quality of the amplifier as a whole.

Make a transformer for a tube amplifier at home

Making a good output transformer at home is quite difficult, but purchasing or ordering one made according to all the rules is not cheap. Recently, there have been proposals to use standard unified transformers such as TAN or TN as output for lamp ultrasonic units. And although in this case you should not count on getting the maximum possible parameters, this option deserves attention due to its accessibility and practicality.

Currently, tube amplifiers used by musicians and released more than 30 years ago still exist. This equipment, as a rule, is “raced” until it is completely worn out. Many years of experience in its operation testify to the reliability of tube amplifiers. Many copies produced, for example, by such companies as BEAG, TESLA, MARC HAL and others, are well preserved. Their repair was most often limited to replacing lamps and electrolytic capacitors.

In more complex cases, it was necessary to replace elements on which the parameters of the amplifiers could depend. Some elements, such as resistors, were destroyed if they malfunctioned. However, it was impossible to determine their denomination from the inscription. It was selected experimentally, as long as the tube amplifier would work, since not all owners and repairmen had circuit diagrams of the equipment.

For these reasons, as well as due to the increased interest in tube circuitry, readers may be interested in the circuits of the most popular pop amplifiers at the end of the last century. These circuits can serve as classic examples of high-quality tube ultrasonic frequencies, which, together with good acoustics, provide the sound quality for which many audiophiles and musicians feel nostalgic.

Simple High Power Tube Amplifier Circuit

Figure 1 shows “Marchal super 100PA”. The tube amplifier provides an output power of 100 W into an 8-ohm load. In this case, the nonlinear distortion coefficient does not exceed 3% (tone controls are set to the middle position). Musicians use a tube amplifier most often as an instrumental amplifier.

The ultrasonic sounder has 4 high-resistance inputs, that is, two parallel: In1 and In2, connected through resistors R1, R2; Vx3 and Vx4, connected through resistors R7 and R8. The mixed signals are amplified in pairs separately on the dual triode VL1 (ECC83) and through the level controls R10 and R13 are fed to the next amplification stage, the VL2 lamp (ECC83), which also serves as a mixer.

In this case, the frequency response at inputs 1 and 2 (at the output of the cathode follower of the second triode VL2) is linear, and at inputs 3 and 4 it has a rise in the high frequency region, which is achieved by passive frequency correction elements C5, C7, R12. The sound effect obtained as a result of such correction is called “diamond”.

In addition, the pre-amplifier has three tone controls separately for low, mid and high frequencies. The low output impedance provided by the cathode follower makes it possible to reduce the interdependence of passive tone controls, assembled according to a simple circuit with a minimum number of parts (variable resistors R19, R20, R21; constant R18; capacitors C9, C11, C12).

The next phase inverter stage (VL3) is also assembled on a double triode ECC83 and has an adjustable frequency correction (variable resistor R30, capacitor C14) in the negative feedback circuit (NFC), which makes it possible to obtain the so-called “presence effect”, i.e. increase in gain in the mid-frequency region (from approximately 2 to 5 kHz) by 6...8 dB.

It should be taken into account that with the chosen adjustment method, due to the weakening of the negative feedback effect, nonlinear distortions increase, which at maximum amplification at a frequency of 3 kHz can amount to 15%, which is acceptable for instrumental sound and is even liked by some musicians, creating a certain timbre coloring. If the ultrasonic sounder assembled according to this scheme is intended to be used as part of an audio complex for playing music or vocals, it is better not to install these elements at all.

The push-pull output stage is assembled using 4 VL4…VL7 lamps of type EL34 (analogue 6P27S), two connected in parallel in each arm. The selected version of the beam tetrode circuit is the simplest, and therefore, for reliable operation with a minimum coefficient of nonlinear distortion, the selection of lamps with identical parameters is required. In practice this is difficult to achieve. You can limit yourself to choosing lamps from one batch (by year and month of production), if they have not been in use before.

As already noted, the parameters of the amplifier largely depend on the correct calculation and high-quality execution of the output transformer T2. For this amplifier model, we were able to find only a brief description of the transformer: magnetic circuit - Ш32x65 plates: the anode winding consists of 4 sections, each section contains 660 turns, wound with PEL wire with a diameter of 0.27 mm (it is better to use PEV with a diameter of 0.32 mm).

Sections 1 and 3, as well as 2 and 4 are connected in parallel, and their pairs are connected in series. The secondary winding also consists of 4 sections of 160 turns of PEL wire with a diameter of 0.67 mm. All sections are connected in parallel. For those who do not have experience in making output transformers on their own, this data may not be enough, since incorrect placement and connection of any of the windings can cause deterioration of parameters and even self-excitation of the amplifier.

A more detailed description of the design of the output transformer, recommendations for the selection of materials and its manufacture for the Marchal amplifier. which in its main parameters is close to that described, are given in. Inductor L1 is made on a magnetic core Ш20х40 and has 200 turns of PEL wire with a diameter of 0.41 mm. Data of power transformer T1: magnetic circuit Ш40х55; primary winding for mains voltage 220 V 450 turns of PEL wire with a diameter of 0.62 mm; The secondary winding for powering the anodes of the lamps consists of two halves of 410 turns each, wound with PEL wire with a diameter of 0.41 mm.

Each half at a rated load must provide an alternating voltage of at least 200 V. A special winding designed to obtain a grid bias (38 V) has 78 turns of PEL wire with a diameter of 0.25 mm. The filament winding contains 15 turns of PEL wire with a diameter of 1.8 mm. At the rated network voltage, it must provide a filament voltage of at least 6.3 V.

Setting up the amplifier begins with setting the bias voltage (-38 V) with trimming resistor R47. In order not to cause significant overheating of the output tubes due to the high quiescent current, before starting the adjustment, the resistor slider is set so that the bias voltage is maximum. By adjusting resistor R45, we achieve a minimum background level, while inputs 1-4 are temporarily connected to the common wire.

Despite the worldwide popularity of Marchal tube pop amplifiers, for most of our musicians they have remained a pipe dream. For obvious reasons, variety equipment produced in the CMEA countries has become much more widespread in our country. Sets of variety equipment from the Hungarian company BEAG were very popular at one time.

Usually the kits consisted of three tube amplifiers: two instrumental, one of which was intended specifically for bass guitar, and one voice. Each tube amplifier was equipped with an acoustic system corresponding to its purpose.

The output stages of the amplifiers were built according to identical push-pull circuits on two EL34 beam tetrodes with a transformer and could develop an output power of up to 60 W at an 8 Ohm active load. Figure 2 shows a diagram of the final stage of the instrumentation amplifier "AEX25SG from BEAG.

It includes:

1. a pre-tube amplifier (the left half of the double triode VL3), the cathode of which is supplied with a common OOS voltage;
2. bass reflex (right half of VL3);
3. push-pull output stage using VL4, VL5 (EL34) tubes with a fixed bias (-42 V).

When the speaker system is turned off, this chain acts as a ballast load. To power the anodes of the amplifier tubes, a rectifier (diodes VD1, VD2), assembled according to a voltage doubling circuit, is used. In this case, the winding of the power transformer T1, which provides the anode voltage (+480 V), must be designed for a current several times greater than that consumed at the rated output power of the amplifier.

Winding T1, designed to produce a bias voltage, should provide an alternating voltage of about 32V, preferably at least 40. Then you can introduce adjustment of the bias voltage by replacing resistor R35 with a tuned one with a resistance of several tens of kilo-ohms. Adjusted resistors RP5 and RP6 are connected to the filament windings, designed to set the minimum background level.

Dual triode tube preamplifier

Figure 3 shows a diagram of the preliminary stages of the AEX250 amplifier. They use two ECC808 dual triodes. The tube amplifier has two identical inputs with separate pre-amplifiers on the VL1 tube and level controls RP1 and RP2, after which the signals are mixed and amplified by a common two-stage amplifier on the VL2 tube.

Passive tone controls for low (RP3) and high (RP4) frequencies are installed between its stages. The circuit does not have any other features. For some capacitors, the operating voltage recommended by the manufacturer is indicated. The AEX650 voice amplifier model, designed to amplify signals from 4 microphones, differs mainly in the construction of preliminary stages.

At the same time, it has separate tone control for low and high frequencies for each input. The amplifier can be connected to the BEAG “AKH200” reverb, built on the principle of magnetic sound recording on a ring tape. Data on output transformers suitable for the output stage of the AEX250 amplifier can be found in the specified literature.