Sound amplifier on tda chips show diagrams. Chip amplifier TDA2030. Detailed description. Structural diagram of the amplifier

A low frequency amplifier (ULF) is such a device for amplifying electrical oscillations corresponding to the frequency range audible to the human ear, i.e. ULF should amplify in the frequency range from 20 Hz to 20 kHz, but some ULF can have a range up to 200 kHz. ULF can be assembled as an independent device, or used in more complex devices - TVs, radios, radios, etc.

The peculiarity of this circuit is that the 11th output of the TDA1552 microcircuit controls the operating modes - Normal or MUTE.

C1, C2 - bypass blocking capacitors, used to cut off the constant component of the sinusoidal signal. Electrolytic capacitors should not be used. It is desirable to place the TDA1552 chip on a heatsink using heat-conducting paste.

In principle, the presented circuits are bridge circuits, since there are 4 amplification channels in one TDA1558Q microassembly case, therefore pins 1 - 2, and 16 - 17 are connected in pairs, and they receive input signals from both channels through capacitors C1 and C2. But if you need an amplifier for four speakers, then you can use the circuit option below, although the power will be 2 times less per channel.

The basis of the design is the TDA1560Q class H microassembly. The maximum power of such a ULF reaches 40 W, with a load of 8 ohms. Such power is provided by an approximately doubled voltage due to the operation of the capacitors.

The output power of the amplifier in the first circuit assembled on the TDA2030 is 60W at a load of 4 ohms and 80W at a load of 2 ohms; TDA2030A 80W at 4 ohm load and 120W at 2 ohm load. The second circuit of the considered ULF is already with an output power of 14 watts.

This is a typical two-channel ULF. With a little piping of passive radio components on this chip, you can assemble an excellent stereo amplifier with an output power of 1 watt per channel.

Microassembly TDA7265 - is a fairly powerful two-channel Hi-Fi class AB amplifier in a typical Multiwatt package, the microcircuit has found its niche in high-quality stereo technology, Hi-Fi class. Simple switching circuits and excellent parameters made the TDA7265 a perfectly balanced and excellent solution for building high-quality amateur radio equipment.

First, a test version was assembled on a breadboard exactly as per the datasheet on the link above, and successfully tested on S90 speakers. The sound is good, but something was missing. After some time, I decided to remake the amplifier according to the modified circuit.

The Micro Assembly is a class AB quad amplifier designed specifically for use in automotive audio applications. Based on this microcircuit, several high-quality ULF variants can be built using a minimum of radio components. The microcircuit can be advised to beginner radio amateurs for home assembly of various acoustic systems.

The main advantage of the amplifier circuit on this microassembly is the presence of four independent channels in it. This power amplifier works in AB mode. It can be used to amplify various stereo signals. If desired, you can connect to the speaker system of a car or a personal computer.

TDA8560Q is just a more powerful analogue of the TDA1557Q chip, widely known to radio amateurs. The developers only strengthened the output stage, thanks to which the ULF is perfect for a two-ohm load.

The LM386 micro-assembly is a ready-made power amplifier that can be used in low-voltage designs. For example, when the circuit is powered by a battery. LM386 has a voltage gain of about 20. But by connecting external resistances and capacitances, you can adjust the gain up to 200, and the output voltage automatically becomes equal to half the supply voltage.

The LM3886 micro-assembly is a high quality amplifier with an output of 68 watts into 4 ohms or 50 watts into 8 ohms. At the peak moment, the output power can reach a value of 135 watts. A wide voltage range from 20 to 94 volts is applicable to the microcircuit. Moreover, you can use both bipolar and unipolar power supplies. The ULF harmonic coefficient is 0.03%. Moreover, this is over the entire frequency range from 20 to 20,000 Hz.

The circuit uses two ICs in a typical connection - KR548UH1 as a microphone amplifier (installed in the PTT) and (TDA2005) in bridge connection as a terminal amplifier (installed in the siren case instead of the original board). As an acoustic emitter, a modified alarm sipen with a magnetic head is used (piezo emitters are not suitable). Improvement consists in disassembling the siren and throwing out the native tweeter with an amplifier. Microphone - electrodynamic. When using an electret microphone (for example, from Chinese handsets), the connection point of the microphone with the capacitor must be connected to + 12V through a resistor ~ 4.7K (after the button!). The 100K resistor in the K548UH1 feedback circuit is better to put with a resistance of ~ 30-47K. This resistor is used to adjust the volume. It is better to install the TDA2004 chip on a small radiator.

To test and operate - with a radiator under the hood, and a tangent in the cabin. Otherwise, squealing due to self-excitation is inevitable. The trimmer resistor sets the volume level so that there is no strong sound distortion and self-excitation. With insufficient volume (for example, a bad microphone) and a clear margin of power of the emitter, you can increase the gain of the microphone amplifier by increasing the value of the trimmer in the feedback circuit several times (the one that is 100K according to the scheme). In a good way - we would need another primambas that does not allow the circuit to self-excite - some kind of phase-shifting chain or a filter for the excitation frequency. Although the scheme and without complications works fine

Full ULF 2x70 Watts on TDA7294.

When assembling an amplifier on chips, TDA7294 is not a bad choice. Well, however, we will not dwell on the technical specifications, you can see them in the PDF file TDA7294_datasheet, located in the download folder for the material for assembling this ULF. As you already understood from the title of the article, this is a full amplifier circuit that contains a power supply, pre-amplification stages with a three-band tone control, implemented on two common 4558 operational amplifiers, two channels of final stages, and a protection node. The circuit diagram is shown below:

With a supply voltage of ±35 volts into an 8 ohm load, you will get 70 watts of power.

The PCB sources are as follows:

PCB LAY6 format:

Arrangement of elements on the amplifier board:

Photo view of LAY board format:

The board has a J5 connector for connecting a temperature sensor (Bimetal Thermostat), it is designated B60-70. In normal mode, its contacts are open, when heated to 60 ° C, the contacts close, the relay disconnects the load. In principle, you can also use thermal sensors with normally closed contacts, designed to operate at 60 ... 70 ° C, only you need to connect it to the gap of the emitter of the transistor Q6 and the common wire, while the J5 connector is not used. If you are not going to use this feature, leave J5 blank.

Operational amplifiers are installed in sockets. Relay for actuation voltage 12 Volts with two groups of switching contacts, contacts must withstand 5 Amperes.

Fuse circuit board LAY6 format:

Photo view of LAY fuse board format:

The protection node power connector is located on the board just above connector J5. Just make a jumper with two wires between this connector and the main power connector as shown in the picture below:

External connections:

Additional Information:

4 Ohm - 2x18V 50Hz
8 Ohm - 2x24V 50Hz

When powered by 2x18V 50Hz:

Resistors R1, R2 - 1 kOhm 2W
Resistor RES - 150 Ohm 2W

When powered by 2x24V 50Hz:

Resistors R1, R2 - 1.5 kOhm 2W
Resistor RES - 300 Ohm 2W

The JRC4558 op amp can be replaced with the NE5532 or TL072.

Please note that on the side of the conductors of the printed circuit board, between the contacts of the relay coil, an LL4148 diode is installed in the SMD version, you can solder the usual 1N4148.

Near the volume control on the board there is a GND point, it is designed to ground the housings of all controls. This piece of bare copper wire is clearly visible in the main picture of the news.

List of elements for repeating the amplifier circuit on the TDA7293 (TDA7294):

Electrolytic Capacitors:

10000mF/50V - 2 pcs.
100mF/50-63V – 9 pcs.
22mF - 5 pcs.
10mF - 6 pcs.
47mF - 2 pcs.
2.2mF - 2 pcs.

Film Capacitors:

1 mF - 8 pcs.
100n - 8 pcs.
6n8 - 2 pcs.
4n7 - 2 pcs.
22n - 2 pcs.
47n - 2 pcs.
100pF - 2 pcs.
47pF - 4 pcs.

Resistors 0.25W:

220R - 1 pc.
680R - 2 pcs.
1K - 6 pcs.
1K5 - 2 pcs.
3K9 - 4 pcs.
10K - 10 pcs.
20K - 2 pcs.
22K - 8 pcs.
30K - 2 pcs.
47K - 4 pcs.
220K - 3 pcs.

Resistors 0.5W:

Resistors 2W:

RES-300R - 2 pcs.
100R - 2 pcs.

Diodes:

Zener diodes 12V 1W - 2 pcs.
1n4148 - 1 pc.
LL4148 - 1 pc.
1n4007 - 3 pcs.
Bridge 8...10A – 1 pc.

Variable resistors:

A50K - 1 pc.
B50K - 3 pcs.

Microcircuits:

NE5532 - 2 pcs.
TDA7293 (TDA7294) - 2 pcs.

Connectors:

3x - 1 pc.
2x - 2 pcs.

Relay - 1 pc.

Transistors:

BC547 - 5 pcs.
LM7812 - 1 pc.

You can download the circuit diagram of the amplifier for TDA7294, TDA7294_datasheet, LAY6 format printed circuit boards in one file from our website. Archive size - 4 Mb.

Article author: Novik P.E.

Introduction

Amplifier design has always been a challenge. Fortunately, in recent years, many integrated solutions have appeared that make life easier for amateur designers. I also did not complicate the task for myself and chose the most simple, high-quality, with a small number of parts, requiring no tuning and stable operation of the amplifier based on the TDA7294 chip from SGS-THOMSON MICROELECTRONICS. Recently, complaints about this microcircuit have spread on the Internet, which were expressed approximately as follows: "spontaneously excited, with incorrect wiring; it burns, for any reason, etc." Nothing like this. You can burn it only by incorrectly switching it on or shorting it out, and cases of excitation have never been noticed, and not only with me. In addition, it has internal protection against short circuits in the load and protection against overheating. It also has a mute function (used to prevent clicks when turned on) and a standby function (when there is no signal). This IC is a ULF class AB. One of the main features of this microcircuit is the use of field-effect transistors in the preliminary and output amplification stages. Its advantages include high output power (up to 100 W at a load of 4 ohms), the ability to work in a wide range of supply voltages, high technical characteristics (low distortion, low noise, wide operating frequency range, etc.), the minimum required external components and low cost

Main characteristics of TDA7294:

Parameter	Conditions	Minimum	Typical	Maximum	Units
Supply voltage		±10		±40	IN
Frequency response	3db signal Output power 1W	20-20000			Hz
Long Term Output Power (RMS)	harmonic distortion 0.5%: Up \u003d ± 35 V, Rn \u003d 8 Ohm Up \u003d ± 31 V, Rn \u003d 6 Ohm Up \u003d ± 27 V, Rn \u003d 4 Ohm	60 60 60	70 70 70		Tue
Peak Musical Output Power (RMS), duration 1 sec.	harmonic factor 10%: Up \u003d ± 38 V, Rn \u003d 8 Ohm Up \u003d ± 33 V, Rn \u003d 6 Ohm Up \u003d ± 29 V, Rn \u003d 4 Ohm		100 100 100		Tue
General harmonic distortion	Po = 5W; 1kHz Po = 0.1-50W; 20-20000Hz		0,005	0,1	%
	Up \u003d ± 27 V, Rn \u003d 4 Ohm: Po = 5W; 1kHz Po = 0.1-50W; 20-20000Hz		0,01		%
Protection operation temperature		145			0C
Quiescent current		20	30	60	mA
Input impedance		100			kOhm
Voltage gain		24	30	40	dB
Peak output current		10			A
Working temperature range		0		70	0C
Case thermal resistance				1,5	0 C/W

(PDF format).

There are a lot of schemes for switching on this microcircuit, I will consider the simplest one:

Typical switching circuit:

Item List:

Position	Name	Type	Quantity
C1	0.47uF	K73-17	1
C2, C4, C5, C10	22uF x 50V	K50-35	4
C3	100 pF		1
C6, C7	220uF x 50V	K50-35	2
C8, C9	0.1uF	K73-17	2
DA1	TDA7294		1
R1	680 ohm	MLT-0.25	1
R2…R4	22 kOhm	MLT-0.25	3
R5	10 kOhm	MLT-0.25	1
R6	47 kOhm	MLT-0.25	1
R7	15 kOhm	MLT-0.25	1

The microcircuit must be installed on a radiator with an area of ​​\u003e 600 cm 2. Be careful, on the microcircuit case there is not a common, but a power minus! When installing a chip on a heatsink, it is better to use thermal paste. It is advisable to lay a dielectric between the microcircuit and the radiator (mica, for example). For the first time, I did not attach any importance to this, I thought, why would I be so scared to close the radiator to the case, but in the process of debugging the design, the tweezers that accidentally fell from the table shorted the radiator to the case. The explosion was great! Chips just smashed to pieces! In general, I got off with a slight fright and $ 10 :). On the board with an amplifier, it is also desirable to supply powerful electrolytes of 10000 microns x 50V, so that at power peaks the wires from the power supply do not give voltage drops. In general, the larger the capacitance of the capacitors on the power supply, the better, as they say, "you can't spoil the porridge with oil." Capacitor C3 can be removed (or not installed), I did just that. As it turned out, it was precisely because of him that when the volume control (a simple variable resistor) was turned on in front of the amplifier, an RC circuit was obtained, which mowed high frequencies when the volume was increased, but in general it is needed to prevent excitation of the amplifier when ultrasound is applied to the input. Instead of C6, C7, I put on the board 10000mk x 50v, C8, C9, you can put any close denomination - these are power filters, they can be in the power supply, or you can solder them by surface mounting, which I did.

Pay:

I personally don't really like to use ready-made boards, for one simple reason - it's hard to find exactly the same size elements. But in an amplifier, the wiring can greatly affect the sound quality, so it's up to you which board to choose. Since I assembled the amplifier immediately for 5-6 channels, respectively, the board immediately for 3 channels:

In vector format (Corel Draw 12)
Amplifier power supply, low-pass filter, etc.

power unit

For some reason, the power supply of the amplifier raises many questions. In fact, right here, everything is quite simple. The transformer, diode bridge and capacitors are the main elements of the power supply. This is enough to assemble the simplest power supply.

To power the power amplifier, voltage stabilization is unimportant, but the capacitances of the capacitors for power supply are important, the more, the better. The thickness of the wires from the power supply to the amplifier is also important.

My power supply is implemented as follows:

The +-15V supply is designed to power the operational amplifiers in the preliminary stages of the amplifier. You can do without additional windings and diode bridges by powering the stabilization module from 40V, but the stabilizer will have to dampen a very large voltage drop, which will lead to significant heating of the stabilizer microcircuits. Stabilizer microcircuits 7805/7905 are imported analogues of our KREN.

Variations of blocks A1 and A2 are possible:

Block A1 is a power supply noise suppression filter.

Block A2 - a block of stabilized voltages + -15V. The first alternative is easy to implement, for powering low-current sources, the second is a high-quality stabilizer, but requires an accurate selection of components (resistors), otherwise you will get a skew of the "+" and "-" shoulders, which will then give a skew of zero on operational amplifiers.

Transformer

The power supply transformer for a 100W stereo amplifier should be approximately 200W. Since I was making a 5-channel amplifier, I needed a more powerful transformer. But I didn’t have to pump out all 100W, and all channels cannot simultaneously take power. I came across a TESLA transformer on the market (below in the photo) watt commercial for 250 - 4 windings with 1.5 mm wire at 17V and 4 windings at 6.3V. By connecting them in series, I got the necessary voltages, although I had to rewind two windings at 17V a little in order to get the total voltage of the two windings ~ 27-30V, since the windings were on top - it was not much work.

A great thing is a toroidal transformer, these are used to power halogens in lamps, there are a lot of them in markets and stores. If structurally two such transformers are placed one on top of the other, the radiation will be mutually compensated, which will reduce interference on the amplifier elements. The trouble is that they have one 12V winding. In our radio market, you can make such a transformer to order, but this pleasure will be well worth it. In principle, you can buy 2 transformers for 100-150W and rewind the secondary windings, the number of turns of the secondary winding will need to be increased by about 2-2.4 times.

Diodes / diode bridges

You can buy imported diode assemblies with a current of 8-12A, this greatly simplifies the design. I used KD 213 pulse diodes, and made a separate bridge for each arm to give a current margin for the diodes. When turned on, powerful capacitors are charged, the current surge is very significant, at a voltage of 40 V and a capacitance of 10,000 μF, the charging current of such a capacitor is ~ 10 A, respectively, along two arms 20A. In this case, the transformer and rectifier diodes briefly operate in short circuit mode. The breakdown of diodes by current will give unpleasant consequences. The diodes were installed on the radiators, but I did not find any heating of the diodes themselves - the radiators were cold. To eliminate power supply interference, it is recommended to install a capacitor ~ 0.33 μF type K73-17 in parallel with each diode in the bridge. I really didn't do it. In the + -15V circuit, you can use bridges of the KTs405 type, for a current of 1-2A.

Design

Finished construction.

The most boring occupation is the body. As a case, I took an old slim case from a personal computer. I had to shorten it a little in depth, although it was not easy. I think that the case turned out to be successful - the power supply is located in a separate compartment and you can put 3 more channels of amplification into the case freely.

After field tests, it turned out that it is not out of place to put the fans on the radiators, despite the fact that the radiators are very impressive in size. I had to make holes in the case from the bottom and top, for good ventilation. The fans are connected through a 100Ω 1W trimmer at the lowest speed (see the following figure).

Amplifier block

Chips are on mica and thermal paste, the screws also need to be isolated. The heatsinks and the board are screwed to the case through dielectric racks.

Input circuits

I really wanted not to do this, only in the hope that this is all temporary ....

After hanging these guts, a small rumble appeared in the speakers, apparently something was wrong with the "ground". I dream of the day when I will throw it all out of the amplifier and use it only as a power amplifier.

Adder board, low-pass filter, phase shifter

Regulation block

Result

The back turned out more beautiful, even though you turn it booty forward ... :)

Construction cost.

TDA 7294	$25,00
capacitors (powerful electrolytes)	$15,00
capacitors (other)	$15,00
connectors	$8,00
power button	$1,00
diodes	$0,50
transformer	$10,50
radiators with coolers	$40,00
resistors	$3,00
variable resistors + knobs	$10,00
biscuit	$5,00
frame	$5,00
operational amplifiers	$4,00
Surge Protectors	$2,00
Total	$144,00

Yes, something came out cheap. Most likely, I didn’t take into account something, I just bought, as always, a lot more, because I still had to experiment, and I burned 2 microcircuits and blew up one powerful electrolyte (I didn’t take all this into account). This is the calculation of the amplifier for 5 channels. As you can see, the heatsinks turned out to be very expensive, I used inexpensive, but massive coolers for processors, at that time (a year and a half ago) they were very good for cooling processors. If you consider that an entry-level receiver can be bought for $240, then you might wonder if you need it :), though there is a lower quality amplifier there. Amplifiers of this class cost about $500.

List of radio elements

Designation	Type	Denomination	Quantity	Note	Shop	My notepad
DA1	Audio amplifier	TDA7294	1			To notepad
C1	Capacitor	0.47uF	1	K73-17		To notepad
C2, C4, C5, C10		22uF x 50V	4	K50-35		To notepad
C3	Capacitor	100 pF	1			To notepad
C6, C7	electrolytic capacitor	220uF x 50V	2	K50-35		To notepad
C8, C9	Capacitor	0.1uF	2	K73-17		To notepad
R1	Resistor	680 ohm	1	MLT-0.25		To notepad
R2-R4	Resistor	22 kOhm	3	MLT-0.25		To notepad
R5	Resistor

Probably, any radio amateur is familiar with the microcircuit: a simple circuit, good sound quality, low price. Recently, I decided to take a look at the other side, again stumbling upon an article about Lincor's "MF-1" amplifier.

This is my first article, it is intended for beginner lovers of good sound. Also presented is a drawing of the PCB and a manufacturing option for the amplifier case.

My introduction didn't go very smoothly. At that time, there were a lot of fakes. They sometimes burned immediately at the first power supply, and if they did start, they did not give out a sound, but something remotely resembling it, because of which I wanted to douse the board with gasoline and set it on fire to get rid of this ULF and never remember about it. Maybe my inexperience was also the reason for this, or maybe the topology of the board of my own manufacture measuring 35 × 45 mm (when remembering that board, large-pimple goosebumps run through the author's body).

After reading, a decision was made to assemble according to the following criteria:
1) a clean ending without a volume control (the amplifier works in conjunction with a PC, and the sound is adjusted from it),
2) 2 amplification channels according to the double mono scheme (there were 2 transformers from UM Vega,
3) lower coefficient. channel penetration and beautiful stereo),
4) forced cooling with the help of 2 computer coolers and fans at low speeds,
5) and all this is mandatory in the case in the form of a finished structure, which is not ashamed to be posted on Datagor.

My version of PP

Strange as it may seem, the home-made amplifier of my neighbor, a former radio amateur, served as the case, assembled in the case of an unknown laboratory device. The amp was put on the landing, because. He was already unnecessarily, but it's a pity to throw it in the trash. I remembered this case when I decided to assemble the MF-1.

In the process of finalizing the hull, simple and inexpensive parts were used:
Aluminum corner 15 × 15 x 1 mm, bought at the Home Center.
M3 bolts with a countersunk head, nuts.
Metal spacers with M3 thread.

And here's what we got:

Transformers and filter

Rectifiers

Terminations with coolers

It's time for the panels. Because We have a fan for cooling, the air must come out somewhere and come in from somewhere. First of all, I started sawing the back panel with an air outlet:

Everything was done with a drill, electric jigsaw, engraver and needle files. Now we cut out the grille from the computer power supply case, clean the edges of the hole:

Now we take soldering acid, a soldering iron with a power of at least 100 W and solder the grate to the panel in several places:

We place input and output connectors on the panel, IT IS MANDATORY TO ISOLATE THEM FROM THE CASE:

We solder the shielding lead of the case to the panel. This will be the ONLY connection between the case and the common power wire. We connect the case to the ground contacts of the input connectors through 1-2 W resistors with a nominal value of 1.5-2 Ohm. These measures are needed in order not to grab the "earth loop", which will spoil us in the form of a 50 Hz background.

Back panel in place:

Now we transfer the Zobel circuit from the board to the PA output connectors. On the board, she does not quite have a place, because. it (the circuit) is a resonant system:

Now it's up to the front panel. It only has a power switch. The panel itself is made of aluminum, behind it is a false panel made of moderately soft plastic, on which you can fix anything with M3 screws with countersunk heads. I used the button from an old dead Wilma-104-Stereo cassette deck:

The panel is mounted on tin corners with hexagon bolts. That's it, the amplifier is ready!

Results

About the sound, I wrote a comment in the topic about:

Guys, I didn't know! I didn't think I'd ever say this, but it's true! Pleasant soft bass, distinct highs (now I can distinguish percussion and hand claps on tracks I know by heart), and all this is a pleasure on homemade three-band TH with 8" woofers.
I want to reassure everyone who is repelled by an increased level of high frequencies: it does not feel like a rise in high frequencies, but as an increase in the quality of the source, an increase in “transparency”.

And I still do not go back on my words. For several months, the amplifier did not bother me at all, as it often happens with me. The sound is not annoying, I want to listen to everything and a lot, no matter at low or high volume.
By the way, about low volume. This ULF has a nice feature: at any volume level, the listener does not lack low frequencies, which can be compared with the use of TKRG, only with smooth (correct) adjustment and without blocking the midrange.

In my version, the board is slightly redone. The choice of "mute" and "standby" modes was thrown out as unnecessary, the main bank of capacitors was moved closer to the MS.

Power supply 2×23 V. KD213B diodes are used in the rectifier. Electrolytes are shunted with a capacity of 100 nF, transformer secondary - 47 nF.
Each MS is isolated from the heatsinks by a mica plate, the heatsinks are in turn grounded to the case.
All wires are twisted together to reduce interference.

The background is not audible even with an open input, even close to the speaker. The goal, so to speak, has been achieved!
Further, the plans are to drill holes for air intake in the right side of the bottom cover of the case, make a fan speed control device with control over the temperature of the radiators, it is possible to build in a preamplifier with a tone control, and paint the case.

- The neighbor got tired of knocking on the battery. He turned the music up louder so that he could not be heard.
(From audiophile folklore).

The epigraph is ironic, but the audiophile is not necessarily “sick in the head” with the physiognomy of Josh Ernest at a briefing on relations with the Russian Federation, who is “rushing” because the neighbors are “happy”. Someone wants to listen to serious music at home as in the hall. The quality of the equipment for this is necessary, which for fans of the decibel of loudness as such simply does not fit where sane people have a mind, but for the latter, this mind comes 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 - the technique of sound reproduction and electronics in general. Which in the digital age are inextricably linked and can become a highly profitable and prestigious profession. The first step in this matter, optimal in all respects, is to make an amplifier with your own hands: it is UMZCH that allows, with initial training based on school physics, on the same table, to go from the simplest structures 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 to cover the first stages of this path for beginners and, perhaps, to tell something new to experienced ones.

Protozoa

So, for starters, let's try to make a sound 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 do not forget to enrich your knowledge base as you progress. But any “smartness” is easier to digest when you see and feel how it works “in hardware”. In this article, further, too, it will not do without theory - in what you need to know at first and what can be explained without formulas and graphs. In the meantime, it will be enough to be able to use the multitester.

Note: if you have not soldered electronics yet, please note that its components must not be overheated! Soldering iron - up to 40 W (better than 25 W), the maximum allowable soldering time without interruption is 10 s. The soldered lead for the heat sink is held 0.5-3 cm from the place of soldering from the side of the device body with medical tweezers. Acid and other active fluxes must not be used! Solder - POS-61.

On the left in fig.- the simplest UMZCH, "which just works." It can be assembled on both germanium and silicon transistors.

On this crumb, it is convenient to master the basics of setting up the UMZCH with direct connections between the cascades, which give the clearest sound:

• Before the first power-up, the load (speaker) is turned off;
• Instead of R1, we solder a chain of a constant resistor of 33 kOhm and a variable (potentiometer) of 270 kOhm, i.e. first note. four times smaller, and the second approx. twice the face value against the original according to the scheme;
• We supply power and, by rotating the potentiometer slider, at the point marked with a cross, set the specified collector current VT1;
• We remove the power, solder the temporary resistors and measure their total resistance;
• As R1, we set the nominal resistor from the standard row closest to the measured one;
• We replace R3 with a constant 470 Ohm chain + 3.3 kOhm potentiometer;
• The same as according to paragraphs. 3-5, incl. a set the voltage equal to half the supply voltage.

Point a, from where the signal is taken to the load, is the so-called. middle point of the amplifier. In UMZCH with unipolar power, half of its value is set in it, and in UMZCH with bipolar power - zero relative to the common wire. This is called adjusting the balance of the amplifier. In unipolar UMZCH with capacitive load decoupling, it is not necessary to turn it off during setup, but it’s better to get used to doing it reflexively: an unbalanced 2-polar amplifier with a connected load can burn its own powerful and expensive output transistors, or even “new, good” and very expensive powerful speaker.

Note: components that require selection when setting up a device in a layout are indicated on the diagrams either with an asterisk (*) or an apostrophe dash (‘).

In the center in the same Fig.- a simple UMZCH on transistors, which already develops 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 such class D amplifier (see below) in cheap Chinese computer speakers, their sound improves markedly. Here we learn another trick: powerful output transistors must be placed on radiators. Components that require additional cooling are circled in the diagrams with a dotted line; however, not always; sometimes - with an indication of the required dissipating area of ​​the heat sink. Adjustment of this UMZCH - balancing with 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 100 W transistor amplifier. You can listen to music through it, but not Hi-Fi, the work class is AB2. However, for scoring a picnic area or an outdoor meeting, a school assembly or a small trading floor, it is quite suitable. An amateur rock band, having such an UMZCH for an instrument, can perform successfully.

In this UMZCH, 2 more tricks appear: firstly, in very powerful amplifiers, the buildup cascade of a powerful output also needs to be cooled, so VT3 is placed on a radiator from 100 sq. see. For output VT4 and VT5, radiators from 400 square meters are needed. see Secondly, UMZCH with bipolar power supply are not balanced at all without load. Either one or the other output transistor goes into cutoff, and the conjugated one goes into saturation. Then, at full supply voltage, current surges during balancing can destroy the output transistors. Therefore, for balancing (R6, did you guess?), the amplifier is powered from +/-24 V, and instead of the load, a 100 ... 200 Ohm wire resistor is included. By the way, the squiggles in some of the resistors in the diagram are Roman numerals, denoting their required heat dissipation power.

Note: a power source for this UMZCH needs a power of 600 watts or more. Smoothing filter capacitors - from 6800 uF to 160 V. In parallel with the electrolytic capacitors of the IP, ceramic ones of 0.01 uF are turned on to prevent self-excitation at ultrasonic frequencies, which can instantly burn out 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 draws on the requirements for entry-level Hi-Fi (if, of course, the UMZCH works on the corresponding acoustic systems, speakers). Powerful field workers do not require much power for buildup, so there is no pre-power cascade. Even powerful field-effect transistors do not burn the speakers under any malfunctions - they themselves burn out faster. Also unpleasant, but still cheaper than changing an expensive bass speaker head (GG). Balancing and generally adjustment to this UMZCH are not required. It has only one drawback, like a design for beginners: powerful field-effect transistors are much more expensive than bipolar ones for an amplifier with the same parameters. IP requirements are the same as before. occasion, but its power is needed from 450 watts. Radiators - from 200 sq. cm.

Note: no need to build powerful UMZCH on field-effect transistors for switching power supplies, for example. computer. When trying to “drive” them into the active mode necessary for the UMZCH, they either simply burn out, or they give a weak sound, but “none” in quality. The same applies to powerful high-voltage bipolar transistors, for example. from the horizontal scanning of old TVs.

Right up

If you have already taken the first steps, then it will be quite natural to want to build UMZCH class Hi-Fi, without going too deep into the theoretical jungle. To do this, you will have to expand the instrument park - you need an oscilloscope, an audio frequency generator (GZCH) and an AC millivoltmeter with the ability to measure the DC component. It is better to take the UMZCH E. Gumeli, described in detail in Radio No. 1 for 1989, as a prototype for repetition. To build it, you will need a few inexpensive affordable components, but the quality meets very high requirements: power up to 60 W, bandwidth 20-20,000 Hz, frequency response unevenness 2 dB, non-linear distortion factor (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 circumstances now known greatly simplify the establishment of this UMZCH, see below. Bearing this in mind and the fact that not everyone succeeds in getting into the Radio archives, it would be appropriate to repeat the main points.

Schemes of a simple high-quality UMZCH

UMZCH Gumeli schemes and specifications for them are given in the illustration. Radiators of output transistors - from 250 sq. see for UMZCH according to fig. 1 and from 150 sq. see for variant according to fig. 3 (numbering is original). The transistors of the pre-output stage (KT814/KT815) are mounted on radiators bent from aluminum plates 75x35 mm 3 mm thick. It is not worth replacing KT814 / KT815 with KT626 / KT961, the sound does not noticeably improve, but it is seriously difficult to establish.

This UMZCH is very critical to the power supply, installation topology and general, therefore, it must be adjusted in a structurally finished form and only with a standard power source. When trying to power from a stabilized IP, the output transistors burn out immediately. Therefore, in fig. drawings of original printed circuit boards and instructions for setting up are given. It can be added to them that, firstly, if “excitation” is noticeable at the first start, they fight with it by changing the inductance L1. Secondly, the leads of the parts installed on the boards must be no longer than 10 mm. Thirdly, it is highly undesirable to change the installation topology, but, if it is very necessary, there must be a frame screen on the side of the conductors (ground loop, highlighted in color in the figure), and the power supply paths must pass outside it.

Note: breaks in the tracks to which the bases of powerful transistors are connected - technological ones, for establishing, after which they are sealed with drops of solder.

The establishment of this UMZCH is greatly simplified, and the risk of encountering "excitation" in the process of use is reduced to zero if:

• Minimize interconnect wiring by placing boards on high-power transistor heatsinks.
• Completely abandon the connectors inside, performing the entire installation only by soldering. Then you will not need R12, R13 in a powerful version or R10 R11 in a less powerful one (they are dotted on the diagrams).
• Use the minimum length of oxygen-free copper audio wires for indoor wiring.

When these conditions are met, there are no problems with excitation, and the establishment of UMZCH is reduced to a routine procedure, described in Fig.

Wires for sound

Audio wires are not idle fiction. The need for their application is now undeniable. In copper with an admixture of oxygen, the thinnest 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 (it seems, due to quantum uncertainties) remains. Enough to be noticed by discerning listeners against the background of the purest sound of modern UMZCH.

Manufacturers and traders without a twinge of conscience slip ordinary electrical copper instead of oxygen-free copper - it is impossible to distinguish one from the other by eye. However, there is a scope where a fake does not go unambiguously: a twisted-pair cable for computer networks. Put a grid with long segments as a “levar”, it will either not start at all, or it will constantly fail. Dispersion of impulses, you know.

The author, when there was still talk about audio wires, realized that, in principle, this was not empty chatter, especially since oxygen-free wires by that time had long been used in special-purpose equipment, with which he was well acquainted with the type of activity. Then I took it and replaced the regular cord of my TDS-7 headphones with a home-made one from a “vitukha” with flexible stranded wires. The sound, by ear, has steadily improved for analog tracks through, i.e. on the way from the studio microphone to the disc, never digitized. Recordings on vinyl made using DMM technology (Direct Meta lMastering, direct metal deposition) sounded especially bright. After that, the interblock editing of all home audio was redone to "vitushny". Then completely random people began to notice the improvement in sound, they were indifferent to music and not forewarned in advance.

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

Video: do-it-yourself twisted-pair interconnect wires

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

Theoretical interlude

As you can see, already at the very beginning of mastering sound engineering, we had to deal with the concept of Hi-Fi (High Fidelity), high fidelity of sound reproduction. Hi-Fi comes in different levels, which are ranked next. main parameters:

1. Band of reproducible frequencies.
2. Dynamic range - the ratio in decibels (dB) of the maximum (peak) output power to the level of self-noise.
3. Self-noise level in dB.
4. Nonlinear distortion factor (THD) at rated (long-term) output power. SOI at peak power is assumed to be 1% or 2% depending on the measurement technique.
5. Irregularities in the amplitude-frequency characteristic (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) audio frequencies.

Note: the ratio of the absolute levels of any values ​​of I in (dB) is defined as P(dB) = 20lg(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 home-made Hi-Fi UMZCH for the home, before moving on to these, you need to clearly understand the requirements for their power required for scoring a given room, dynamic range (dynamics), self-noise level and SOI. To achieve a frequency band of 20-20,000 Hz from the UMZCH with a blockage at the edges of 3 dB and a frequency response unevenness at the midrange of 2 dB on a modern element base is not very difficult.

Volume

The power of the UMZCH is not an end in itself, it should provide the optimal volume of sound reproduction in a given room. It can be determined by curves of equal loudness, see fig. Natural noise in residential premises is quieter than 20 dB; 20 dB is the wilderness in complete calm. The volume level of 20 dB relative to the threshold of hearing is the threshold of intelligibility - you can still make out the whisper, but the music is perceived only as a fact of its presence. An experienced musician can tell which instrument is playing, but not exactly what.

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

90 dB is the volume level of a symphony orchestra in a very good concert hall. 110 dB can give out an expanded 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 perceived even as distinguishable in meaning with an effort of will, but already annoying noise. The loudness zone in residential premises of 20-110 dB is the zone of full audibility, and 40-90 dB is the zone of the best audibility, in which unprepared and inexperienced listeners fully perceive the meaning of the sound. If, of course, he is in it.

Power

Calculating the power of the equipment for 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) speakers. In this case, the UMZCH will not noticeably add its distortions to those speakers, they are already the main source of non-linearity in the audio path. But the UMZCH should not be made too powerful: in this case, the level of its own noise may be above the threshold of audibility, because. it is considered from the voltage level of the output signal at maximum power. If we consider it very simply, then for a room of an ordinary apartment or house and speakers with normal characteristic sensitivity (sound output), we can take a 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 watts.
• 70-100 sq. m - 100-150 watts.
• 100-120 sq. m - 150-200 watts.
• Over 120 sq. m - is determined by calculation according to acoustic measurements on site.

Dynamics

The dynamic range of UMZCH is determined by equal loudness curves 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. Sound with dynamics of 80-85 dB in a city apartment will not be distinguished from ideal by any expert.
2. Other serious musical genres - 75 dB is excellent, 80 dB is over the roof.
3. Pops of any kind and movie soundtracks - 66 dB for the eyes is enough, because. these opuses are already compressed in levels up to 66 dB and even up to 40 dB during recording, so that you can listen to anything.

The dynamic range of the UMZCH, correctly selected for a given room, is considered equal to its own noise level, taken with a + sign, this is the so-called. signal-to-noise ratio.

SOI

Nonlinear distortions (NI) UMZCH are the components of the spectrum of the output signal, which were not in the input. 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. 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 it is difficult to assess the timbre of the sound. In people without a musical ear, the masking effect is already observed at 45-40 dB of volume. Therefore, UMZCH with a THD of 0.1% (-60 dB from a volume level of 110 dB) will be assessed as a Hi-Fi by an ordinary listener, and with a THD of 0.01% (-80 dB) can be considered not distorting the sound.

Lamps

The last statement, perhaps, will cause rejection, up to furious, among adherents of tube circuitry: they say that only tubes give real sound, and not just any, but certain types of octal ones. Calm down, gentlemen - a special tube sound is not fiction. The reason is fundamentally different distortion spectra for electronic tubes and transistors. Which, in turn, are due to the fact that the electron flow in the lamp moves in a vacuum and quantum effects do not appear in it. A transistor is a quantum device, where minor charge carriers (electrons and holes) move in a crystal, which is generally impossible without quantum effects. Therefore, the spectrum of tube distortions is short and clean: only harmonics up to the 3rd - 4th are clearly traced in it, and there are very few combination components (sums and differences of the frequencies of the input signal and their harmonics). Therefore, in the days of vacuum circuitry, SOI was called the harmonic coefficient (KH). In transistors, the distortion spectrum (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, the designers of transistorized UMZCH took for them the usual "tube" SOI of 1-2%; a sound with a tube distortion spectrum of this magnitude is perceived by ordinary listeners as clean. By the way, the very concept of Hi-Fi did not exist then. It turned out - they sound dull and deaf. In the process of the development of transistor technology, an understanding was developed of what Hi-Fi is and what is needed for it.

At present, the growing pains of transistor technology have been successfully overcome and side frequencies at the output of a good UMZCH are hardly captured by special measurement methods. And lamp circuitry can be considered to have passed into the category of art. Its basis can be any, why can't electronics go there? An analogy with photography would be appropriate here. No one can deny that a modern digital SLR gives an image immeasurably clearer, more detailed, deeper in terms of brightness and color range than a plywood box with an accordion. But someone with the coolest Nikon "clicks pictures" like "this is my fat cat got drunk like a bastard and sleeps with his paws spread", and someone with Smena-8M on a Svemov b / w film takes a picture in front of which people are crowding at a prestigious exhibition.

Note: and once again calm down - not everything is so bad. To date, low-power lamp UMZCHs have at least one application left, and not of the least importance, for which they are technically necessary.

Experimental stand

Many audio lovers, having barely learned how to solder, immediately "go into the lamps." This is by no means deserving of condemnation, on the contrary. Interest in the origins is always justified and useful, and electronics has become such on lamps. The first computers were tube-based, and the on-board electronic equipment of the first spacecraft was also tube-based: there were already transistors at that time, but they could not withstand extraterrestrial radiation. By the way, then, under the strictest secrecy, tube ... microcircuits were also created! Cold cathode microlamps. The only known mention of them in open sources is in the rare book by Mitrofanov and Pickersgil "Modern receiving-amplifying lamps".

But enough of the lyrics, let's get down to business. For those who like to tinker with the lamps in fig. - a diagram of a bench lamp UMZCH, designed 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 slight refinement touched only the output transformer: now you can not only “drive” your native 6P7S in different modes, but also select the screen grid switching ratio 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. See below for output transformer manufacturing.

Guitarists and rockers

This is the case when you can not 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 pass through a special prefix - fuser - deliberately distorting its spectrum. Without this, the sound of the string was too sharp and short, because. an electromagnetic pickup reacts only to the modes of its mechanical oscillations in the plane of the soundboard of the instrument.

An unpleasant circumstance soon emerged: the sound of an electric guitar with a fuser gains full strength and brightness only at high volumes. This is especially evident for guitars with a humbucker pickup, which gives the most "evil" sound. But what about a beginner, forced to rehearse at home? Do not go to the hall to perform, not knowing exactly how the instrument will sound there. And just rock lovers 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 outrageous surroundings.

So, it turned out that the fatal sound appears at volume levels acceptable for residential premises, if the UMZCH is tube. The reason is the specific interaction of the signal spectrum from the fuser with a clean 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 contour and the light for viewing.

Those who need a tube amplifier not for experiments, but because of technical necessity, have no time to master the intricacies of tube electronics for a long time, they are passionate about others. UMZCH in this case, it is better to do transformerless. More precisely, with a single-ended matching output transformer that operates without constant bias. This approach greatly simplifies and speeds up the manufacture of the most complex and critical assembly of the lamp UMZCH.

“Transformerless” UMZCH tube output stage and preamplifiers 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 options for a preamplifier for it. Above - with a tone control according to the classic Baksandal scheme, which provides a fairly deep adjustment, but introduces small phase distortions into the signal, which can be significant when operating the UMZCH on a 2-way speaker. Below is a simpler preamplifier with tone control that does not distort the signal.

But let's get back to the end. In a number of foreign sources, this circuit is considered a revelation, however, identical to it, with the exception of the capacity of electrolytic capacitors, is found in the Soviet Radio Amateur's Handbook of 1966. A thick book of 1060 pages. There was no Internet then and databases on disks.

In the same place, on the right in the figure, the shortcomings of this scheme are briefly but clearly described. Improved, from the same source, 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 through the load. If, instead of high-impedance speakers, you turn on a matching transformer with a conventional speaker, as in the previous. 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 a 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 stray 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", buzzes or squeaks. Foucault currents are fought by reducing the thickness of the plates of the magnetic circuit and additionally isolating them with varnish during assembly. For output transformers, the optimal thickness of the plates is 0.15 mm, the maximum allowable is 0.25 mm. Thinner plates should not be taken for the output transformer: the fill factor of the core (the central core of the magnetic circuit) with steel will fall, the cross section of the magnetic circuit will have to be increased to obtain a given power, which will only increase distortion and losses in it.

In the core of an audio transformer operating with a constant bias (eg, 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 bias; on the other hand, in a conventional magnetic circuit it increases the stray field and requires a larger core. 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 plates (punched), pos. 1 in fig. In them, a non-magnetic gap is formed during the penetration of the core and therefore is 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 closes are solid. Shp plates are often used to assemble transformer cores without magnetization, because Shp plates are made of high quality transformer steel. In this case, the core is assembled in an overlap (the plates are placed with a notch in one direction or the other), and its cross section is increased by 10% against the calculated one.

It is better to wind transformers without magnetization on USh cores (reduced height with widened windows), pos. 2. In them, the reduction of 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 also made from them. Then the assembly of the core is carried out in a cut: a package of W-plates is assembled, a strip of non-conductive non-magnetic material is laid with a thickness equal to the value of the non-magnetic gap, covered with a yoke from a package of jumpers and pulled together by a clip.

Note:"Audio" signal magnetic circuits of the ShLM type for output transformers of high-quality tube amplifiers are of little use, they have a large stray field.

At pos. 3 is a diagram of the dimensions of the core for calculating the transformer, at pos. 4 winding frame design, and on pos. 5 - patterns of its details. As for the transformer for the "transformerless" output stage, it is better to do it on the SLMme with an overlap, because. the bias is negligible (the bias current is equal to the current of the screen grid). 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 turn out to be much less than 800 ohms. The more free space left in the windows, the better the transformer turned out. Therefore, the windings wind turn to turn (if there is no winding machine, this is a terrible machine) from the thinnest possible wire, the anode winding laying coefficient for the mechanical calculation of the transformer is taken as 0.6. The winding wire is of the PETV or PEMM brands, they have an oxygen-free core. It is not necessary to take PETV-2 or PEMM-2, they have an increased outer diameter due to double varnishing and the scattering field will be larger. The primary winding is wound first, because. it is its stray field that most affects the sound.

Iron for this transformer must be looked for with holes in the corners of the plates and clamps (see the figure on the right), because. "For complete happiness" the assembly of the magnetic circuit is carried out in the following. order (of course, the windings with leads and outer insulation should already be on the frame):

1. Prepare half-diluted acrylic varnish or, in the old fashioned way, shellac;
2. Plates with jumpers are quickly varnished on one side and put into the frame as quickly as possible, without pressing hard. The first plate is placed with the lacquered side inward, the next - with the unvarnished side to the lacquered first, etc.;
3. When the frame window is full, staples are applied and tightened tightly with bolts;
4. After 1-3 minutes, when the extrusion of varnish from the gaps apparently stops, the plates are added 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 or the like. 3-5 days.

The core assembled using this technology has very good plate insulation and steel filling. Losses due to magnetostriction are not detected at all. But keep in mind - for the cores of their permalloy, this technique is not applicable, because. from strong mechanical influences, the magnetic properties of permalloy irreversibly deteriorate!

On microchips

UMZCH on integrated circuits (ICs) is most often done by those who are satisfied with sound quality up to average Hi-Fi, but are more attracted by cheapness, speed, ease of assembly and the complete absence of any adjustment procedures that require special knowledge. Simply, an amplifier on microcircuits is the best option for dummies. The classic of the genre here is UMZCH on the TDA2004 IC, standing on the series, God forbid, for 20 years, 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 on a very low-resistance, up to 1.6 Ohm, load, which allows you to remove full power when powered from the 12 V on-board network, and 7-8 W - with a 6-volt power supply, for example, on a motorcycle. However, the TDA2004 output in class B is non-complementary (on transistors of the same conductivity), so the sound is definitely not Hi-Fi: THD 1%, dynamics 45 dB.

The more modern TDA7261 gives no better sound, but more powerful, up to 25 W, because. the upper limit of the supply voltage has been increased to 25V. TDA7261 can be run from almost all on-board networks, except for aircraft 27 V. With the help of hinged components (strapping, on the right in the figure), TDA7261 can operate in mutation mode and with the St-By (Stand By, wait) function, which switches the UMZCH to the minimum power consumption mode when there is no input signal for a certain time. Amenities cost money, so for a stereo you will need a pair of TDA7261 with radiators from 250 sq. see for each.

Note: if you are 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 TDA7482, on the left in the figure, working in the so-called. class D. Such UMZCH are sometimes called digital amplifiers, which is not true. For true digitization, level samples are taken from an analog signal at a quantization frequency of at least twice the highest of the reproducible frequencies, the value of each sample is recorded in an error-correcting code and stored for future use. UMZCH class D - pulsed. In them, the analogue is directly converted into a sequence of high-frequency pulse-width modulated (PWM) pulses, which is fed to the speaker through a low-pass filter (LPF).

Class D sound has nothing to do with Hi-Fi: THD of 2% and dynamics of 55 dB for UMZCH class D are considered very good indicators. And TDA7482 here, I must say, the choice is not optimal: other companies specializing in class D produce UMZCH ICs cheaper and require less strapping, for example, the Paxx D-UMZCH series, on the right in Fig.

Of the TDAs, it should be noted the 4-channel TDA7385, see the figure, on which you can assemble a good amplifier for speakers up to medium Hi-Fi inclusive, with frequency separation into 2 bands or for a system with a subwoofer. The filtering of low-frequency and mid-high frequencies in both cases is done at the input on a weak signal, which simplifies the design of the filters and allows for a deeper separation of the bands. And if the acoustics are subwoofer, then 2 channels of the TDA7385 can be allocated for the sub-ULF of the bridge circuit (see below), and the remaining 2 can be used for midrange-high frequencies.

UMZCH for subwoofer

A subwoofer, which can be translated as a "subwoofer" or, literally, "a subwoofer" reproduces frequencies up to 150-200 Hz, in this range, human ears are practically unable to determine the direction to the sound source. In speakers with a subwoofer, the “subwoofer” speaker is placed in a separate acoustic design, this is the subwoofer as such. The subwoofer is placed, in principle, as it is more convenient, 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. Connoisseurs agree that it is still 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 with consumers with normal hearing and not particularly demanding.

“Leakage” of midrange-high frequencies into the subwoofer, and from it into the air, greatly spoils the stereo, but if you sharply “cut off” the subbass, which, by the way, is very difficult and expensive, then a very unpleasant sound jump effect will occur. Therefore, channel filtering in subwoofer systems is done twice. At the input, MF-HF with bass "tails" are distinguished by electric filters, which do not overload the MF-HF 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, it is already acoustic in the subwoofer: the subwoofer is placed, for example, in the partition between the resonator chambers of the subwoofer that do not let the midrange out, see on the right in Fig.

A number of specific requirements are imposed on the UMZCH for a subwoofer, of which the "dummies" consider the greatest possible power to be the main one. This is completely wrong, if, say, the calculation of acoustics for a room gave peak power W for one speaker, then the power of the subwoofer needs 0.8 (2W) or 1.6W. For example, if speakers S-30 are suitable for the room, then a subwoofer is needed 1.6x30 \u003d 48 watts.

It is much more important to ensure the absence of phase and transient distortions: if they go, there will definitely be a sound jump. As for THD, it is acceptable up to 1%. Bass distortions of this level are not audible (see equal loudness curves), and the “tails” of their spectrum in the best audible midrange region will not get out of the subwoofer.

In order 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 UMZCH are turned on in the opposite direction through the speaker; the signals to the inputs are in antiphase. The absence of phase and transient distortion in the bridge circuit is due to the complete electrical symmetry of the output signal paths. The identity of the amplifiers that form the shoulders of the bridge is ensured by the use of paired UMZCH 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 the 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 the R5C3 and R'5C'3 circuits. Radiator area TDA2030 - from 400 sq. see. Bridge UMZCHs with an open output have an unpleasant feature: when the bridge is unbalanced, a constant component appears in the load current that can disable the speaker, and protection circuits on the subbass often fail, turning off the speaker when not needed. Therefore, it is better to protect the expensive “dubovo” woofer with non-polar batteries of electrolytic capacitors (highlighted in color, and the diagram of one battery is given in the sidebar.

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 sufficiently durable non-ringing plastic, for example, polyethylene. The inner diameter of the pipes is 60 mm, the protrusions inward are 113 mm in the large chamber and 61 in the small one. For a specific speaker head, the subwoofer will have to be reconfigured for the best bass and, at the same time, for the least impact on the stereo effect. To tune the pipes, they take obviously longer lengths and, pushing in and out, achieve the desired sound. The outward protrusions of the pipes do not affect the sound, they are then cut off. The pipe settings are interdependent, so you have to tinker.

Headphone Amplifier

A headphone amplifier is made by hand most often for 2 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 build up "buttons" or "burdocks". The second is for high-end home headphones. Hi-Fi UMZCH for an ordinary living room is needed with dynamics up to 70-75 dB, but the dynamic range of the best modern stereo headphones exceeds 100 dB. An amplifier with such dynamics is more expensive than some cars, and its power will be from 200 watts per channel, which is too much for an ordinary apartment: listening at a very low power level 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 a makeweight are obviously too high.

The diagram of the simplest headphone amplifier on transistors is given in pos. 1 fig. Sound - except for Chinese "buttons", works in class B. It also does not differ in efficiency - 13-mm lithium batteries last for 3-4 hours at full volume. At pos. 2 - TDA classic for on-the-go headphones. The sound, however, gives quite decent, up to average Hi-Fi, depending on the parameters of the track digitization. Amateur improvements to the TDA7050 strapping are innumerable, but no one has yet achieved the transition of sound to the next level of class: the “mikruha” itself does not allow. TDA7057 (pos. 3) is simply more functional, you can connect the volume control on a regular, not dual, potentiometer.

UMZCH for headphones on the TDA7350 (pos. 4) is already designed to build up good individual acoustics. It is on this IC that headphone amplifiers are assembled in most household UMZCHs of the middle and high class. The UMZCH for headphones on the KA2206B (pos. 5) is already considered professional: its maximum power of 2.3 W is enough to drive such serious isodynamic "burdocks" as TDS-7 and TDS-15.