The simplest circuit for a 20 watt audio amplifier. Professional power amplifiers. Fully assembled ULF circuit
Greetings to all who looked at the light. The review will focus, as you probably already guessed, on a budget class AB stereo amplifier (car amplifier), which can be easily used as an amplifier for home speakers, in the country, in a car, etc. Thanks to the presence of a tone block (bass and treble), volume and balance controls, as well as a stylish appearance, good sound quality and sufficiently high output power, it will easily fit into a home interior as a budget amplifier for stereo speakers, if any.
General view of the Kinter MA-180 stereo amplifier:
Brief performance characteristics:
- Rated output power - 2x20 W (4 ohms)
- Maximum output power - 2x35 W (4 ohms)
- Specialized IC - - TDA7377, AB class
- THD (stereo mode, 10W) - 0.3%
- Signal to noise ratio - 100 dB
- Sensitivity - 0.25-50 mV
- Power supply - 12V/5A
- Load resistance - 4-16 Ohm
- Frequency response: 20Hz-20kHz
- Input connectors: RCA input (tulip), mini Jack 3.5mm
- Output connectors: screw-on socket for stereo sound, USB 5V
- Adjustment: volume/balance/treble/bass
- Presence of protection - yes (temperature, polarity reversal, overvoltage, short circuit)
- Dimensions - 155mm*102mm*42mm
- Weight - 247gr
Equipment:
The stereo amplifier is delivered in a compact cardboard box in blue tones, it contains the main characteristics: 
Inside the box, apart from the amplifier itself, there is nothing, the amplifier itself is wrapped in a little bubble wrap, there are also no instructions: 
The dimensions of the amplifier are quite small, only 155mm * 102mm * 42mm: 
The weight is also miserable, only 247g: 
Now the stereo amplifier itself:
As you can see, the appearance is quite stylish: 
On the front panel are all the necessary controls (bass/treble/balance/volume), as well as the power button. On the side ribs there are holes for attaching the amplifier to something: 
The regulators are soft, when turning the knob there is absolutely no crackling and extraneous noise. Also, when power is applied, the backlight of the volume control will turn on. It looks quite impressive, it does not depend on the position of the knob, nor on the volume, i.e. changes smoothly by itself in an arbitrary order: 
On the rear panel, standard connectors for connecting: 
- on the left is an input connector for a standard mini-jack (headphones) - you can send a signal from a PC, smartphone, player or any device with an AUX output (radio, for example). Those. the signal to be amplified
- further two analog RCA connectors (tulips, white for the left channel, red for the right) - mainly for connecting old video equipment: VCRs, DVD players, etc.
- block with 4 spring-loaded output connectors - for direct connection of speakers (right and left channels, plus red, minus black)
- 5V USB output - for charging electronic gadgets
- on the right DC Port power supply 12V/5A. The output power and sound quality directly depend on the quality of the PSU / adapter. A low-power adapter will not be able to deliver all the declared power, a PSU without proper noise filtering will “glow”, so use reliable, proven PSUs with a declared current of at least 2A (PSU / Adapters from chargers for batteries, laptops, LED strips, etc., or, at worst, a 12V output from the PC connector). I use a PSU from an Opus BT-C3100 V2.2 charger at 12V / 3A, I mentioned an atypical application in that article: 
With this power supply, there is practically no extraneous noise. For my Soviet 8W speakers 8AC-3 is enough for the eyes (two 4W speakers 4GD-35 / 8GDSH-1): 
Stereo Amplifier Disassembly:
As you can see, the binding of parts is minimal, and even then, due to the fact that the tone block on the op-amp TL072CP is used: 
Directly as an amplifier, a specialized AB class TDA7377 microcircuit is used, with a rated power of 40W in bridge mode: 
The case of a stereo amplifier is used as a radiator, because. It is aluminum and gives off heat well. There is thermal paste between the case and the microcircuit, somewhat reminiscent of our Russian KPT-8: 
At an average output power, the case practically does not heat up, at almost maximum it is slightly warm, which indicates a fairly good efficiency of the microcircuit.
Here is the datasheet for the chip: 
As you can see, it contains a minimum binding of parts and has all kinds of protection against short circuit, polarity reversal, overvoltage, overheating and can be turned on in various combinations, so if you have the desire and skills to work with a soldering iron, you can redo the wiring for a 2.1 configuration (stereo speakers and a subwoofer) or 4 (quad acoustics): 
To connect, use a copper speaker cable if possible: 
It is enough to strip the cable insulation a little and just plug the wires into the appropriate connector - thanks to the spring-loaded pads, the contact is excellent and holds tight. If possible, do not confuse the polarity of the speakers, otherwise the speakers will play in "opposite phase", which is not very good for the sound.
The input wire can be used like this (two mini Jack "daddy"): 
The USB output connector is located very inconveniently - on the rear panel next to the power connector, and even with a low power supply / adapter, it is better not to connect voracious devices. In this case, USB is only for charging: 
A small video of the work (the volume is maximum, the speakers do not pull out the bass at the maximum, they start to “squish”, recording on the SGS3 smartphone):
The smartphone does not transmit all the volume, in fact it is quite loud. At medium volume, the bases are excellent, "juicy". Before that, there was a self-propelled gun on the TDA8561Q, I didn’t like the bass at all ...
Developer Wishes:
- build in a power supply unit of sufficient power
- add switch for different configurations (2, 2.1, 4)
- make the backlight of the regulator change in time with the music, or depending on the position of the regulator (maximum speed - red on, medium volume - green)
- add headphone output
- add rubber feet
Pros:
+ Good sound quality
+ Stylish appearance
+ Universal (due to its compact size and widespread power supply, you can take it out of town, connect car audio)
+ Sufficient power output
+ Virtually no heat
+ The presence of a tone block
+ Availability of USB output
+ Easily customizable
+ The case can be used for a more powerful chip (class D, 50-100W)
Minuses:
- bit big price
- not everyone in the household has an extra PSU / adapter for 12V / 2-5A
- there are no rubberized legs (you can scratch the table, it is treated by sticking 2-3 layers of adhesive tape / electrical tape)
Conclusion: a good ready-made amplifier for those who are too lazy to assemble with their own hands. Personally, I liked the sound, there is enough power with a margin. As a budget stereo amplifier, it fits perfectly, I recommend it for purchase!
Audio Power Amplifier 20W- this ULF was created on the basis of the LM1876 chip, and this, in turn, is a modification of the well-known dual low-frequency amplifier LM1875. The LM1876 chip was originally created for dynamic radiators and can freely deliver 20 W of power to two channels with a load resistance of 4 ohms, while the non-linear distortion coefficient is only 0.09%. Below is a schematic diagram, signet and specification of the device.
Not so long ago, one of the sites published a circuit of a power amplifier implemented using the TDA2003 chip and capable of working both with headphones and voicing small rooms. But judging by the numerous responses, his sound is still not what we would like. Therefore, I propose to those who wish to repeat a more powerful version of the UMZCH using the LM1876 chip. p>
Schematic diagram of the LM1876 amplifier
This device receives supply voltage from a two-polar power supply, which includes a toroidal transformer with two windings for 15v alternating voltage with a midpoint output. After the rectifier and the filter circuit, consisting of two electrolytic capacitors with a capacity of 6800 uF, the constant voltage for powering this microcircuit is already within ± 20v. The inductors L1 and L2 installed in the diode bridge circuit serve to reduce network interference.
The audio signal comes through a conventional stereo input connector built into the printed circuit board. There is also a balanced potentiometer for adjusting the sound level. This potentiometer also has the function of switching the amplifier to a standby state, while the current consumption of the microcircuit is only 3.8 mA. Acoustic systems are connected to the power amplifier through "tulip" connectors, which are also built into the board.
To create comfortable working conditions for the device, a microcircuit that is very hot must be installed on a cooling radiator with an effective heat dissipation area of at least 120 mm2. With an amplifier output power of 20 W, the power consumption will be approximately 38 W, this is if the load resistance is 4 ohms, and at 8 ohms it will be about 20 watts. The critical temperature for a chip chip is within 170C. Based on this, the heat sink must be selected as much as possible, that is, as far as the size of the case can allow. In this case, there will be fewer trips of the chip protection system in case of overheating. Also, when attaching a chip to a heatsink, it is necessary to apply a layer of heat-conducting paste KPT-8 on its substrate - this will significantly reduce thermal resistance. Below you can download everything you need to create a power amplifier.
Here is a photo of the finished ULF
In places, stock photos are used, due to the lack of their own in proper quality. Carefully! There is a carpet in the photo, do not look for carpet-phobes :) A lot of large photos, traffic!
Greetings! As promised, I'll tell you about how I collected the power for acoustics. Since the industrial options did not suit me, I aimed my choice at diy options. The amplifier will be used with high-sensitivity bookshelf acoustics, I decided that I would assemble a 15-30 W amplifier, always in class A (Yes, yes, instead of a heater). I went through a lot of projects, settled on the Krell KSA 50 clone - HifiDIY A20. He completely arranged for me, power, dimensions, components. And I started assembling.
A few technical specifications:
Frequency range：5 - 100000 kHz
Output power in class A: 25 W / 8 ohms
Output power in class AB: 100 W / 8 ohms
Distortion: 0.01%
Dimensions (WxHxD): 25x13x32 cm
Purchase:
Everything is standard, I ordered, paid, and eighteen days later I received this beauty:
Fortunately, the packaging was excellent, there was not a scratch on the amplifier, and the box clearly played football, but everything was as usual.
Power supply assembly:
The power supply is made according to the standard scheme, the upc1237 chip is used as protection, it is she who, because it requires a minimum of strapping and is quite reliable. The total filter capacitance is 88000 uF. The transformer is universal, two primary 110 each, for our networks, must be connected in series, and four secondary 16 V at 6 A.
This is how to connect the windings:
And more clearly:
Everything started right away, in fact, it could not be otherwise :) We begin to assemble amplification boards. I plan to put a soft start soon, since when charging the containers, the power supply works in an almost short circuit.
Reinforcing part assembly:
The amplifier is assembled on fairly high-quality components, nichicon muse capacitors, 1% dale resistors, omron relays. Everything goes according to the usual principle, from small to large, first we prepare the board and form the conclusions of the resistors:
We soldered the resistors, soldered the capacitors, diodes (do not confuse the direction of switching on) and zener diodes (do not confuse either :))
Now the capacitors and emitter resistors of the output transistors:
The power terminals must be soldered on both sides, and that is, there is a risk of tearing them out, the terminals are put on tightly:
Now the missing transistors, relays, variable resistors:
Now we put the thermal stabilization transistor, attached to the output:
We prepare the radiator, you can degrease and wipe it with alcohol, screw the racks:
Fitting:
Don't forget about bushings and substrates:
Now we install the output transistors, we also do not forget about the substrates, the bushings are no longer needed:
Do not forget to fix the thermal stabilization transistor and the diode bridge:
The preparation for the test run was over, I assembled it, turned it on, there was no noise, no crunch, cod, hmm, after a couple of seconds there was smoke from v +, I was very lucky that the flux burned out and not a piece of the track on the board. I checked everything probably five times, I can’t find an error, in a bad mood I postponed the assembly the next day. Then in the morning it dawned on me, I should have checked the weekends, if I had confused npn with pnp, as it turned out, I confused it, yes, a shame, but what to do, I redid it and the amplifier immediately started up. Hooray!
Finished boards:
Now you need to turn on the design and adjust the quiescent current and zero at the output, set it to zero, then the quiescent current: I have 500 mA per transistor, 2 A per channel, more is possible, but at room temperature of + 23 ° C, the case heats up to 50 -60 ° C and this is not the limit :) The quiescent current is set on the resistor R20, the value is measured between d6 and q10. First you need to set a lower value than necessary, with the heating of the structure, the quiescent current creeps up, it is necessary to warm up the amplifier to operating temperature within half an hour - an hour, and only then set the current, after setting the current, set the output to zero, it is regulated by resistor R13 , and the current value is measured between r21 and j4. That's all, the setup is complete, it's time to assemble the amplifier into the case.
Assembling the body:
To begin with, let's assemble the back panel, I did not connect xlr, but the amplifier can also be used with a balanced connection, only two amplifiers are required, one per channel. I really liked the switch, it immediately opens the phase and zero, it is very convenient so that you do not accidentally grab anything during assembly.
We fasten the legs to the chassis and put the power supply:
We begin to assemble the chassis, the layout is VERY dense, it turned out that at the end of the assembly I did all the operations with tweezers. It turned out like this:
He took the power wires as far as possible from the signal wires, used a shielded wire, a 2.5 mm 2 cable goes to the output terminals, which is generally enough. There was no fastening for the indicator illumination, I simply attached it with ties to the signal one. The glass with the logo was glued with superglue. The wire to the output connectors is soldered very tightly, I even had a 70 watt soldering station stuck :) So you need an old-fashioned tin for buckets :)
Results:
The amplifier turned out to be not big, but heavy, but with excellent sound, it will delight me with its sound on cold evenings, 360 W of heat is dissipated on the case, after all :)
Scheme:
Amplifier circuit
Power Supply Diagram
Improvement ideas:
- There are 2 polar electrolytes in the OOS circuit, connected by pluses, replace them with a high-quality non-polar electrolyte (Something like Nichicon ES)
- Current sources for input differential stages - on 2 resistors and a zener diode - should be replaced with something on a transistor.
- Add soft start.
Finished product:
Alexey, why not start asking questions more consciously? Then you can answer more accurately. It's not me because here I am such a guru all in white, and he is "beeped" despicable there, I'll drag him with a face on the table - no, of course. But either "... components can be used or not to increase power ...", or "... there is enough power ..." - there is one thing here, you see. And if you are interested in why the output transistors are heated, then they would immediately ask about it.
And, again, in order. "the problem is in the other output they are heating up" - how is this to be understood? The output of the amplifier is two wires, signal and common, are they heated in your presentation?
Ok, we are still talking about excessive, in your opinion, heating of the output transistors. They are "warming up are all 4 transistors on the radiator" - I'll try to filter this stream. They heat up - which means "heat up", within certain limits, these transistors should heat up. Are they heated under a signal at high power or are they heated without a signal? To what temperature are they heated - if approximately, then the finger tolerates (it is 50-60 degrees) or can the kettle be boiled on the radiator?
Not specified.
"all 4 transistors on the radiator from the comet tape recorder" - so what? Alexey, a variety of models of Kometa tape recorders from the 50s to the end of Soviet times were released a little more than a fig, this is again about nothing. What are the dimensions of the heatsink and what is the measured power rating of the amplifier at what size load?
Not specified.
"maybe the radiator is too small" - but who the hell knows, maybe it's too small. Or maybe just right. Or maybe the quiescent current is too big. What is the quiescent current? What is it like when you turn it on, that is, on a cold amplifier, and what is it like after running the amplifier without a signal for 20-30 minutes? Why is such a value of this current chosen, and not more and not less?
Not specified.
"at the exit kt 819" - again: so what? KT819 in plastic or KT819 in metal - not indicated - these varieties have a different contact area with the radiator, plastic ones, all other things being equal, heat up a little more, that's okay.
You see, Alexey, you put questions in such a way that it is hardly possible to answer on your situation with all your desire. Therefore, some reasons for overheating of the output transistors are rather abstract:
This is so, on the go I remembered. Maybe someone else will remember. And putting two output transistors in parallel with such an output power makes no sense: at normal load and in normal mode, single ones will pull without any problems. KT819 will definitely be pulled.
For good, you don’t need to invent what else to screw on, but measure the transistor modes and see with an oscilloscope what happens in the circuit both without a signal and when working from sine and pulse generators; what we have at idle, and what - under load or its equivalent. Such a conversation will be substantive, but for now everything is reminiscent of an attempt to describe today's weather based on the sensations on a drooling finger exposed in the window.
And the first thing is to be able to correctly formulate the task: what is observed, what does not suit, what are we striving for and what costs along this path will be considered acceptable.
And then, Alexey, they will help you more effectively.
Amplifiers running on 12V DC tend not to have a lot of power, and also, they are not HiFi class. But this little amp has good performance. When powered at 14.4V it delivers 20W per channel into a 4 ohm load, and the harmonic distortion at lower power levels is typically less than 0.03%.
This is the perfect project for those who want a compact stereo amplifier that can run on a 12V battery. It can be used in cars, outdoor recreation, country houses or anywhere else.
The design is simple and safe to repeat by beginner radio amateurs, since there is no danger of electric shock from the network.
Compared to the TDA1519A version, this TDA-7377-based amplifier has a significantly improved signal-to-noise ratio, and the harmonic distortion coefficient is about 50 times better - under typical conditions no more than 0.03%.
In addition, the power consumption of the amplifier in standby mode is low - no more than 1 watt. As a result, if you do not squeeze the maximum out of it, but use it in nominal mode, then it will not drain the battery too quickly.
And because the amplifier has a self-protection circuit, it is practically “fireproof”. In case of overheating or short circuit, self-limiting or load disconnection will be activated accordingly.
Main characteristics of TDA7377:
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Schematic diagram:
Pin assignment TDA7377:
| 1 | OUT1 | Exit 1 |
| 2 | OUT2 | Exit 2 |
| 3 | Vcc | “+” power |
| 4 | IN1 | Input 1 |
| 5 | IN2 | Input 2 |
| 6 | SVR | Exit 1 |
| 7 | stand-by | Switch input “Mute/Stand by” |
| 8 | PW-GND | Output stage ground |
| 9 | S-GND | signal ground |
| 10 | DIAG | Diagnostic output |
| 11 | IN4 | Input 4 |
| 12 | IN3 | Entrance 3 |
| 13 | Vcc | “+” power |
| 14 | OUT4 | Exit 4 |
| 15 | OUT3 | Exit 3 |
With a 12V supply, the maximum amplitude that a conventional amplifier can generate is ±6V. This results in a meager 4.5 watts into a 4 ohm load, or 2.25 watts into an 8 ohm load, not counting the loss in the output transistors. . Even if the DC power is around 14.4V (the maximum you would normally expect from a 12V car battery), the power will increase to 6.48W and 3.24W for 4 ohm and 8 ohm loads respectively - not quite enough for consumers.
There are three common solutions to this problem. The first is the use of a DC converter in the key mode to increase the supply voltage. However, this greatly increases the cost and complexity of the amplifier, although this is one way to get much more power from a 12V supply. But we wanted to keep this project simple, which eliminates this technique.
Parts layout:
There are options for increasing the power of the amplifier, for example, the use of the H-architecture, but with some deterioration in the harmonic distortion factor. In this case, the amplifier itself provides the key mode.
The second way is to reduce the impedance of the loudspeakers. Some car speakers have an impedance of 2 ohms, which allows you to double the power, at the same supply voltage. However, we did not limit the use of this amplifier to 2 Ohm loudspeakers.