What is the article about
In this article I will tell you how I assembled an inexpensive stereo amplifier (2 channels of 11 W Rn = 2 Ohm) with a separate channel for electric guitar (22 W Rn = 4 Ohm) from a minimum of parts on a single TDA1558Q chip.
Such an amplifier is convenient in that you can turn on the accompaniment (or “backing track”) through the stereo channel by removing the signal from the player (computer, music center, etc.) and play solo on the electric guitar, or you can connect a second guitar or bass to the stereo channel . Such an amplifier with speakers can successfully replace cheap low-power computer speakers.
How it all started
It all started with the purchase of an electric guitar - I became interested in music, and I wanted to learn how to play this very electric guitar. Quite an expensive pleasure, I must say: the guitar itself + combo + gadgets + all sorts of cords and straps result in a decent amount. In general, I bought one guitar, connected it to a computer with an output to the already mentioned three-watt speakers ...
ABOUT NOTHING! (but you can download all sorts of effects there on your computer).
Connected to music center at 175 watts through the microphone input ... NOTHING! (lots of background and sound without effects)

First of all, I soldered a simple “Distortion” pedal on two transistors according to the scheme from the Radio magazine. I assembled the circuit, turned it on - it does not work. Why? I checked and checked, it’s not clear, everything is working, everything should be fine ... In general, I put it aside, not knowing what to do with it. And then after a couple of weeks, I turned it on again - it all works, only the signal is weak, and there are a lot of pickups, the circuit without a case - i.e. not shielded at all. I bent the body of thin sheet steel, put the “button” (foot switch), it’s fine, I still use it. The sound is not super-mego, but for such a simple scheme, it’s quite okay. In addition to the effect, it simultaneously amplifies the weak signal of the guitar.

There was no desire to buy an inexpensive combo of low power and dubious quality, but at a rather tangible price for a student's pocket. Soviet ten-watt speakers were found at home - it was decided to make an amplifier for them.

It started!
I found a circuit on the TDA1558Q car radio chip. At some forum I saw that people adapted it for approximately the same columns as mine found, good feedback. Inexpensive, a minimum of details in the circuit - excellent! The microcircuit produces 4 channels of 11 W, in another inclusion - 2 channels of 22 W.
I started to do it according to a two-channel scheme, I already etched the board, but changed my mind and decided to redo it, but not into a four-channel one, but into three. Like this:

The result was a 2.1 system amp circuit, i.e. 2 speakers and a subwoofer, but I have other goals assigned to it ... :laughing:
According to the scheme, I think there should be no questions, except that the switch between 5 and 14 pins and two grounds confuses. When pin 14 is disconnected from the power source, the microcircuit is switched to standby mode with a current consumption of less than 14 μA, I did not get smart with this switch and simply connected pins 5 and 14 with a track. As for the ground, here it is recommended to make a signal ground and a separate power ground, as I understand it, this allows you to reduce the background. I have everything on the same earth, the background is almost inaudible.
Unfortunately, I didn’t have a printed circuit board drawing, I advise you to do it on a breadboard (that’s what it’s called) - it’s all in holes, and pads around them. So it will be faster and easier. In addition, if the tracks for the microcircuit are drawn by hand (like me), and not on a printer, then they turn out to be thin and quite close to each other.
The microcircuit needs powerful block power supply and necessarily a radiator.
I went to a computer engineer friend, bought a used one from him computer block power supply for 150r, and also, out of the kindness of his heart, Gennady gave me the same, but a dead power supply, a radiator and a couple of connectors, for which special thanks to him!
I disassembled the non-working power supply and placed the circuit of my amplifier in its case. My speakers, unfortunately, turned out to be from different pairs and even for different resistances ... Therefore, at first I used only the most powerful channel, because. there was nothing to connect to the stereo.

This is what it looked like inside:

And this is how it is outside!

I probably used the amplifier in this form for half a year, it works - and okay. :laughing: But, nevertheless, the absence of any adjustments at all made me finish it (before, I even adjusted the volume on a lotion or guitar).
I stumbled upon this site, read Andrew's article and decided to make myself a marshal's timbre block for this article.

I took the scheme and denominations of these:


I puzzled for a long time how to make a headphone output when the whole circuit is on mikruha and without pre-amplification. In the end, I decided to just add a simple mini-amp circuit with overload (in addition, there will be a built-in effect in the amplifier). True, it does not provide for overload shutdown, i.e. You won't be able to play on clear sound with headphones.

Here is a schematic:

The scheme worked for me right away. True, I expected more amplification ... There are enough headphones, but she could not shake a small speaker. By the way, there is some strange nominal value of the volume control here - I did not find such, I set the variable to 10 kOhm, and it regulates normally with it. :laughing:

Frame
I assembled the body from plywood. I did not shrink with the dimensions, so that there was still more inside free place- and it’s better for cooling, and so that in the process of improvements and upgrades, something else from the electronics could be placed there.
The bottom, front and rear walls are the basis of the case, they are made of 12 mm plywood, the side walls and the cover are made of 6 mm plywood. Sawed with an electric jigsaw. Everything is fastened with screws.
The front panel and plate with output connectors (on the rear wall) are cut out of sheet steel with a thickness of about 1 mm.
Here is such a yet not very pretty case looming:

Assembly
Next, all the electronics must be fixed in the case. I removed the power supply cover, unscrewed the screws that secure the board, carefully pulled it out and drilled 4 holes in the bottom of the power supply. Through these holes, I screwed the power supply to the bottom of the amplifier case with countersunk screws. I glued a piece of electrical tape on the hats so that the screws would not close any tracks from the bottom of the board, and assembled the power supply back.
The amplifier board is attached to the bottom with screws, and the tone block and headphone amplifier circuit are screwed on the front panel with potentiometer nuts.
View from above:

Tone block:

Mini amplifier circuit with overdrive for headphones:

The guitar part of the amplifier is ready, it turned out like this:

From the back it looks like this:

We turn on, check, connect the guitar, turn the knobs, rejoice. :laughing:

In the stereo channel, a dual 47 kΩ potentiometer is used as a volume control. Those. socket (stereojack) - potentiometer - circuit on TDA1558Q - 2 output sockets. Everything is simple.

Decor
Numerous plywood chips and cracks as an element of decor did not suit me, too vintage look! Therefore, I decided to glue the body with a wood-like adhesive film with a beautiful structure (sold in hardware stores, it costs about 50 rubles per meter). It was possible to glue it in such a way as to cover some of the screws, but I specially glued the parts separately so as not to complicate the disassembly of the case.
I thought how I would sign the front panel. The stencil would look like "Don't stand under the arrow!" or "Don't get in - he'll kill you!", but somehow you need to sign. :laughing: I wanted to make an inscription in some graphics editor and in the copy center print on a transparent self-adhesive. And then the idea came to try to make a similar thing at home.

BDSM method of making stickers with inscriptions
A way for people with strong nerves, I must say. :laughing:
Go! You take a strip of wide adhesive tape (5 cm) of the desired length with a margin on both sides, put it on the table with the sticky side up. You hold the edges (stocks) and write, from right to left in mirror reflection the desired inscription with a regular ballpoint pen (I wrote in black). The difficulty lies in the fact that you need to write carefully, the first time, do not smear anything with your fingers and not make a mistake, because you write backwards. It is better to write a mirror inscription on a piece of paper first, and then copy it so as not to confuse anything. For convenience, I also glued a metal ruler to make it smoother, it was more convenient to hold the strip and there was less chance of smearing my hands. A rather dubious technology, but with accuracy and at least some artistic ability, you can get a pretty decent sticker. :laughing:
In the process:

And here is the finished sticker:

It turned out quite marketable, I'm happy with the result. Unless, the inscriptions didn’t quite turn out under the handles, I shifted the entire sticker to the right, but that’s okay, I’m already finding fault ...

They glued the body and made an inscription on the front panel:

We carefully lay all the wires, put the cover in place:

That, in fact, is all, the final touch remains in the form of beautiful knobs for potentiometers.

Epilogue
This is my first most "serious" design, do not judge strictly, somewhere there may be inaccuracies, some errors.
In my opinion, it turned out to be a pretty good universal device for a very reasonable price. Of course, this is not a tube “head”, but at the level of cheap combos, I think this is a very good option. Not very convenient only in terms of selecting acoustics for a stereo channel - a resistance of 2 ohms. :no:
Perhaps a lot of improvements and alterations. Since the power supply outputs 12V and 5V and has a power of 400W (!), It would be nice to use it for other circuits. For example, you can bring a couple of terminals to the rear panel and, if it is possible to eliminate the harmful effects of one source, power a preamplifier, or a lotion, or something else from it. You can experiment with the values ​​of the tone block, you can put some kind of filter for the signal, etc.
In the future - the selection of acoustics, the elimination possible errors, assembling the preamp as a separate unit or a tube overdrive.

How to make a low power tube combo from old parts. Single ended output stage

I made this small low-power tube guitar amp a long time ago, probably about 15 years ago. It was my first design assembled on electronic tubes Oh. Since I was not involved in lamp technology at that time, I did not have stocks of more or less high-quality components for such a design. And in general, for me it was an experiment. The case for this compact combo amplifier was then made by my friend, carpenter and guitar master Oleg Gnilitsky. Electronic components were literally found "in the landfill" and in my electronic trash. I unscrewed the output transformer from some old tube TV, lamp panels are also from some old lamp technology. I used a power transformer of the TAN 16-220-50 type. This excellent transformer was available in my "electronic stocks". After rummaging through my cabinets and drawers for an hour, I scraped a few old 6N2P and 6P14P type lamps of unknown origin onto the surface of this world. I suggested that some of these Soviet-made lamps might still be in working order. And so it turned out. And by the way, we must give them their due, these lamps are still working in the combo.

This low-power amp was used for several years for home rehearsals and then, when other equipment appeared, it was pushed into the far corner in an electronic trash warehouse and undeservedly forgotten. Recently I was sorting through this electronic rubbish and found this miracle device. I cleaned it of dust, plugged it into the network and it turned out that it works fine to this day. I just had to clean and lubricate the rustling and creaking potentiometers and the small amp again like new. So I decided to publish this article on my website. I think it will be useful for those who are starting to learn about tube technology and want to make a cheap small tube amplifier.

Looking ahead, I’ll say that instead of 6N2P and 6P14P, you can use the now more common 12AX7 and EL84 lamps in this combo. The EL84 output lamp is a complete analogue of 6P14P, and when using 12AX7, you need to change the connection diagram of its filament circuits, which will be discussed in this article.

EL84 and 6P14P lamp pinout

Lamp pinout 6N2P

Lamp pinout 12AX7

The 6N2P double triode filament circuit is designed for a voltage of 6.3 volts. The filament voltage must be applied to the legs 4 and 5 of the lamp. The 12AX7 lamp heater is also connected to legs 4 and 5, but is rated at 12.6 V. However, the 12AX7 lamp filament circuit can also be powered from 6.3 V, since the connection point of the lamp halves heaters is brought to leg 9. Since each of the lamp halves heaters 12.6 V is designed for the same 6.3 V, we can connect them in parallel and use this lamp instead of 6N2P. To do this, the legs 4 and 5 of the 12AX7 lamp must be connected together, and the filament voltage must be applied to terminal 9 and to the legs 4 and 5 connected together.

Schematic diagram of a small-sized tube guitar amp. Click on the diagram to enlarge it

The guitar is connected to the J1 jack. At the input of the amplifier, the level control on the potentiometer R1 is turned on. From the potentiometer engine through the resistor R2, the signal is fed to the grid of the first triode of the VL1 lamp. Resistor R2 serves to prevent the lamp from working with an unconnected grid in the event of an open in the circuit of the potentiometer R1 engine (malfunctions in potentiometers often occur).

From the cascade output (VL1-a triode anode) amplified signal is fed to a three-band tone control that provides high, mid, and low frequencies. From the output of the tone control (potentiometer slider R6), the signal is fed to the level control "Master". A small loudness of this regulator is achieved by turning on a capacitor with a capacity of 680 picofarads between the slider and the top output of the potentiometer according to the circuit. As a result, when the volume is reduced, the proportion of high frequencies in the output signal slightly increases. Next, the signal goes to the second voltage amplification stage, assembled on the second half of the lamp - the VL1-b triode. From the anode of this triode, through the coupling capacitor C9, the signal is fed to the output stage of the amplifier.

The output stage is assembled according to a single-cycle circuit on two lamps VL2 and VL3 of the 6P14P (EL84) type, connected in parallel. Parallel connection of two lamps allows you to slightly increase the output power of the amplifier. You can use only one lamp, leaving the second socket empty. this is how I use the combo, because at home its output power and sound volume is more than enough for me. With one tube, the output power of the amplifier is 2..3 watts. If you install a second lamp, the power will be around 5 watts. Due to the fact that the tube output stage has a signal clipping characteristic different from transistor circuits, one can (subjectively) say that a "tube" three watts is much louder than a "transistor" three watts. Although this statement sounds at first glance unscientific, but in reality it is all about the nature of the distortion introduced by tube circuits into the signal when overloaded. The distortion of a tube circuit is not as sharp as in a transistor circuit, and therefore a tube amplifier can operate in the saturation region while producing a rather pleasant sound, while transistor circuits, when overloaded, limit the signal very sharply, immediately turning it into a semblance rectangular pulses, which causes very unpleasant distortion to the ear. For this reason transistor amplifier should have a much larger gain margin than a tube one. As you can see, there is no mysticism here and everything fits into the laws of physics.

The loudspeaker of the combo has a coil resistance of 8 ohms. It is connected via an output transformer. The output transformer is a very responsible and most expensive part. tube amplifier. The sound of such an amplifier, its frequency range is highly dependent on the quality and design of the output transformer. Tube amplifiers designed for listening to music often use expensive and difficult to wind ultra-linear transformers. Because a guitar amp doesn't need as wide a frequency range as an amp designed for listening to music, a guitar amp doesn't have the same high demands on the output transformer. It can even be said that for a guitar amplifier, too wide a frequency range is even harmful. A large amount of high frequencies leads to the appearance of "sand" in the guitar sound. Therefore, loudspeakers intended for use in guitar amps are made with an upper limit of reproducible frequencies in the region of 7 - 8 kilohertz. Frequencies above this border should be clipped, as this is a "sand" area. It must be canceled that in amplifiers and amplifiers for classical (acoustic) guitars, everything is just the opposite. Them frequency characteristics just very close to "musical" amplifiers. So we are talking only about amplifiers for electric guitars. For the same reason, "guitar" amplifiers are not very suitable for listening to music.

In my mini amp, I used an output transformer from an old tube TV. Such a transformer is quite suitable for a small guitar amplifier and is in good agreement with the output tube, since exactly the same 6P14P tubes were used on the TV. The loudspeaker is connected to the secondary winding of the transformer through a conventional telephone jack. This is a common solution in guitar amps. You can disable the internal speaker and connect to this jack outer column. There is also a headphone jack. Headphones are switched on through a voltage divider on resistors R22 and R23. The divider is connected to the amplifier output automatically when the speaker plug is removed from the socket.

Schematic diagram of the power supply of a tube guitar amp

The weak point of my combo is the loudspeaker. Strictly speaking, the used dynamic head is not a "guitar" head, I didn't have any guitar speakers at that time and I installed a Japanese speaker with a power of 3 W, once torn out of some old Japanese radiogram. Although the speaker is not bad, but it is not "guitar", that is, it is quite broadband and reproduces frequencies that are not needed for the guitar signal, lying in the "sand" area. To some extent, this is offset by a not very broadband output transformer and the presence of a tone control. But all the same, in acoustics for an electric guitar, it is better to use special "guitar" dynamic heads.

Switch Sw2 "Tone" includes capacitor C14, which shunts resistor R19 in the cathode circuit of the output lama. In this case, the sound becomes brighter and the output power of the amplifier increases slightly. Chain C11 R22 eliminates the possible self-excitation of the amplifier.

The power supply unit of the combo is assembled on the basis of the unified Soviet transformer TAN16-220-50 (Transformer Anodno-Nakalny). This transformer is very convenient for use in homemade lamp designs, as it has all the necessary voltages to power both incandescent and anode lamp circuits. nevertheless, you can use any transformer, for example, from an old tube TV or a homemade one. The transformer must contain at least 2 secondary windings. Filament, for a voltage of 6.3 V (and a current sufficient to power the incandescent lamps) and a high-voltage winding with a voltage of 250 - 270 volts. In the case of the TAN16-220-50 transformer, I connected several of its secondary windings in series to get a voltage of about 210 volts. This transformer has 2 filament windings for 6.3 V. so I "shushed" and powered each lamp from its own winding. Nobody bothers to connect the heaters of both lamps to the same filament winding in parallel, if there is only one such winding in your transformer. A 470 ohm resistor R26 is included in the filament circuit of the first lama. Its engine is connected to the "ground". While tuning the amplifier, we turn the R26 slider, achieving a minimum of background alternating current in dynamics. the setting must be made with the R1 knob set to the minimum volume position.

I used the winding of the transformer 15-16 to 24 volts to connect the power-on indication LED to it. Switch SW2 enables or disables the anode voltage. This is done in order to extend the life of the lamps. As you know, the life of electronic tubes is reduced if the anode voltage is applied immediately at the moment the amplifier is turned on, while the filaments have not yet warmed up. Therefore, first we turn on the amplifier in the network, wait for the lamps to warm up (2-3 minutes) and then turn on the anode voltage with switch Sw2.

Mr. Shanti. June 2018

Chassis and hinged mounting amplifier tube guitar amp. View from above

I'll add a couple of articles:

Well, I won’t talk about circuitry and how everything works in this article. We will assemble the case and put everything into it.

Guitar amp (do-it-yourself combo) is the most common amplifier that is used by guitarists, bass players and other guitarists for rehearsals and playing them. I wrote the type of wisdom.

Guitar amp it can have different shapes, it can be in the form of an amplifier and a speaker in one case, the guitar is plugged directly into it and played happily. This is one of the most popular amplifier-to-speaker layouts. Knuckles and sockets can be placed either vertically or frontally. Also, an amplifier can be related to a speaker, as a head (a box with an amplifier) ​​is related to a cabinet (a box with speakers).

And so we will make a combo - what is needed for this.

1 - Straight arms - distributed in childhood.

2 - Vacation for 7 calendar days - you can ask the director

3 - Speaker (Special guitar breed) - taken from the World of Music store

4 - 2 boards from IKEA.

5 - corners from a cheap combo.

6 - wheels - are taken to the OBI for 58 rubles. (spinning)

In order to screw this colossus, which weighs quite a lot, to a wooden case, I attached side walls with ears for which I will screw the chassis. Everything is cut with metal scissors and fastened with rivets (a riveter in OBI costs 270 rubles, 3.2 mm rivets are inserted into a 3.5 mm hole, bolts are bought there for screwing lamp panels, bolts with M3 thread)

For convenience, I recommend using electric tools, a jigsaw and a screwdriver ... Otherwise, believe me, I even got tired of sawing them, and a manual hanger in general. Well, duck here ... cabinet 40 * 42 * 28 cm. For strength, I glued the corners, glued them with epoxy resin. It seizes within an hour - one and a half, but dries out completely in a day. For strength, it is better to fasten with self-tapping screws.

By mutual agreement, after conferring with my wife, we decided that the iron mesh does not roll.

In the OBI hardware store, we accidentally found just such a thing. She reminded me how the amplifiers of the 60s were covered and I decided that I would have it blue with such a muzzle. In order to stretch, a frame was made and the mesh was pinned to the frame with a construction stapler.

And so, we continue.

I ordered blue vinyl and black corners from Penza (Erasov).

Here I found the most detailed videos on assembling and tightening the cab.

I especially want to highlight this video.

And so we studied the question "How to fit the amp?" and let's get down to business!
From the beginning, I covered all the holes and cracks with wood putty.

Usually the corners are rounded. This can be done either with a cut-in, and if it’s not there by chance, then for example, I just tilted the base of the jigsaw at the angle I needed and went through removing the extra corners.

Then we take a black bologna and lightly go through it on the outside where the speaker will be and on the inside, you don’t need to fill it with paint! Just enough to give a dark tint. These are purely aesthetic aspects.

Demo video so you can listen to how the sound turned out.

And so - stating a fact - do-it-yourself combo it's real, it's quite possible to play Heavy Metal on fender!

One of these days I ran out of money. I am a student and spend all my time studying. You won't earn anywhere. But life gave me a guitar and the ability to play this tool. So I decided to make some money. I walked around the city, played and earned money on that. There was no special profit, but I really liked this occupation. A cheap guitar pickup was sent from China. All that was left was to purchase a sound amplifier. The cheapest branded one I found was $150. I don’t have that kind of money, so I set a goal to assemble the amplifier myself - to make it cheaper.

Scheme

For this purpose, I didn’t accelerate much for power and chose a simple amplifier on the TDA8560 chip. This chip costs about $ 3. The ULF circuit is very simple and can be assembled in a hinged way. So did it the first time. The microcircuit must be attached to a rather large radiator. In order not to install additional cooling elements. The power wires must be taken thick in order to avoid their melting and short circuiting of the system in the future.

There are several protections in the microcircuit itself. She is not afraid of replays. overvoltage, but still you should not torment her and experiment. All other elements are very easy to find in old radio equipment. All their total cost will not exceed $2.

Later, he transferred his device to a printed circuit board, since long trips around the city significantly dangled the structure inside the column. I made a printed circuit board using the laser iron method, there are quite a lot of articles on this topic on the Internet.

All parts were carefully soldered, did not overheat during this operation.
Installed a radiator. I connected the speakers to the circuit, made an input to the music feed 3.5 mm jack (for the guitar pickup), connected the battery.

All this neatly arranged in the body of the old column. The total weight was approximately 8 kg. My speaker is only 45 watts.

The amplifier gives out 50. I don’t even load it especially. Works with a bang. Satisfied with the simplicity and assembly scheme. The battery is a regular lead gel battery, 12 V.

Total

The total cost is $10. The benefit regarding the purchase of a ready-made kit is $140. Now everyone hears me and people do not pass by). At minimal cost received maximum effect and pleasure. Choose for yourself what you spend, 150 dollars or one day of your life. Good luck to everyone) AptuneR.

They brought me a case, somehow battered by life, from the American PEAVEY guitar combo and asked me to assemble a guitar amplifier in it.
The assembly of the amplifier took a long time and lasted more than a year. It was my first combo. There have been many experiments and many preamplifier circuits have been tried. I either threw the whole thing into a corner for a long time, then I took up the experiments again.
However, I have had good experience. And in the spring of this year, I finally assembled the finished structure.

The article presents the results of my work. The amp has two channels: "Guitar" and "Bass", and an honest 50 watts of sound.

The case is pretty battered, but I didn’t do anything with it, it gives it a vintage look.

Even before me, some do-it-yourselfer assembled an amplifier inside. But the result was so disgusting that they brought it to me. Many thanks to this unknown solderer for a good transformer, which was very useful for powering my fifty-watt version of the UMZCH!

Combo preamp schematic

Guitar channel: mode switching "Clean/Drive"(clean/overdrive), gain control Gain and volume control Drive Volume in mode Drive.

Bass channel: volume/gain control volume. Common tone controls for both channels "Bass", "Middle", "Treble".
Master output volume control Master.

According to the scheme, I will only talk about the most important. RC chains C4R4, C5R7, C6R8, C7R10 correct the frequency response as we need: emphasizing and shaping the most delicious frequencies of the guitar range. Without them, the sound would be too "flat", dull and inexpressive.

Diodes serve to limit the amplitude at the peaks, again forming the “same sound”.

The resistance of the P7 potentiometer can be set to 470K - 1M instead of 100K, then the drive in the "Drive" mode will be much more and it will be possible to play heavier things.

About the details

Capacitors C1, C3, C8, C10, C11, C19, C18 - ceramic multilayer. C12, C13, C16, C17 - electrolytic, Jamicon. All the rest are domestic film type K73-17.
Resistors with a power of 0.125-0.25 W.
OU KA4558 or analogues of other companies, for example BA4558, NJM4558.

The final amplifier of the combo, aka UMZCH

The circuit is a classic of the genre, only a current mirror on transistors VT4, VT5 has been added.

Resistors R12, R13 with a power of 2-5 watts.

Transistor VT7 is installed on the heat sink of one of the output transistors.

The output transistors are mounted on heat sinks with an area of ​​at least 400 cm2 each.

Capacitors C6, C7 MBM are soldered in close proximity to the cases of the output transistors, connecting the second terminal to the chassis.

Establishment of UMZCH

Let's turn on the positive and negative branches of the power supply by a lamp, the voltage of which is not less than the supply voltage, you can take lamps 230V to 60W. The protective ability of an incandescent lamp is based on the property that there is a big difference between its cold and hot resistance.

If the amplifier is working well, the quiescent current is about 30-40 mA. With such a current, the incandescent lamp due to the small "cold resistance" is equivalent to a conductor (short circuit), as if it were not in the circuit. In other words, when the lamp is off, everything is in order.

If the lamp is on, this indicates a large current consumption and the presence of some kind of malfunction in the circuit. However, a catastrophe will not happen, because. the increased resistance of the heated lamp filament limited the current, which reduced the likelihood of damage to parts of the amplifier (usually the output transistors).

The quiescent current of 30-40 mA is set by the trimming resistor R7. If its adjustment is not enough, you need to reduce the resistance of the resistor R8.

Experience shows that a large quiescent current arises due to incorrect installation resistors, board defects, poor soldering, high frequency self-excitation and, much less frequently, bad parts.

Power Supply Diagram

The winding for powering the amplifier must have a voltage of 2 × 26 V at a current of at least 2 A.

Resistors R1, R2 are needed to limit the input voltage of the 7815/7915 stabilizers.

All common wires must be brought together at one point, this is the key to clear sound and stable uninterrupted operation of the device as a whole.

I have all Jamicon capacitors. C1, C2 must be at least 50 Volts, and C3, C4 at least 25 Volts.

Files and samples

▼ 🕗 16/06/08 ⚖️ 21.86 Kb ⇣ 361 Hello reader! My name is Igor, I'm 45, I'm a Siberian and an avid amateur electronics engineer. I came up with, created and maintain this wonderful site since 2006.
For more than 10 years, our magazine exists only at my expense.

Good! The freebie is over. If you want files and useful articles - help me!