This article will discuss a fairly common and popular amplifier chip TDA7294. Let's look at its brief description, technical characteristics, typical connection diagrams and give a diagram of an amplifier with a printed circuit board.
Description of the TDA7294 chip
The TDA7294 chip is a monolithic integrated circuit in a MULTIWATT15 package. It is intended for use as an AB Hi-Fi audio amplifier. Thanks to its wide supply voltage range and high output current, the TDA7294 is capable of delivering high output power into 4 ohm and 8 ohm speaker impedances.
The TDA7294 has low noise, low distortion, good ripple rejection, and can operate from a wide range of supply voltages. The chip has built-in short circuit protection and an overheat shutdown circuit. The built-in Mute function makes it easy to control the amplifier remotely, preventing noise.
This integrated amplifier is easy to use and does not require many external components to function properly.
TDA7294 Specifications
Chip dimensions:
As stated above, chip TDA7294 is produced in the MULTIWATT15 housing and has the following pinout arrangement:
- GND (common wire)
- Inverting Input
- Non Inverting Input
- In+Mute
- N.C. (not used)
- Bootstrap
- Stand-by
- N.C. (not used)
- N.C. (not used)
- +Vs (plus power)
- Out
- -Vs (minus power)
You should pay attention to the fact that the microcircuit body is connected not to the common power line, but to the power supply minus (pin 15)
Typical TDA7294 connection diagram from datasheet
Bridge connection diagram
Bridged connection is the connection of an amplifier to speakers, in which the channels of a stereo amplifier operate in the mode of monoblock power amplifiers. They amplify the same signal, but in antiphase. In this case, the speaker is connected between the two outputs of the amplification channels. Bridge connection allows you to significantly increase the power of the amplifier
In fact, this bridge circuit from the datasheet is nothing more than two simple amplifiers to the outputs to which an audio speaker is connected. This connection circuit can only be used with speaker impedances of 8 Ohms or 16 Ohms. With a 4 ohm speaker, there is a high probability of the chip failing.
Among integrated power amplifiers, the TDA7294 is a direct competitor to the LM3886.
Example of using TDA7294
This is a simple 70 watt amplifier circuit. Capacitors must be rated for at least 50 volts. For normal operation of the circuit, the TDA7294 chip must be installed on a radiator with an area of about 500 cm2. The installation is carried out on a single-sided board made according to .
Printed circuit board and arrangement of elements on it:
Amplifier power supply TDA7294
To power an amplifier with a 4 Ohm load, the power supply must be 27 volts; with a speaker impedance of 8 Ohms, the voltage should already be 35 volts.
The power supply for the TDA7294 amplifier consists of a step-down transformer Tr1 having a secondary winding of 40 volts (50 volts with a load of 8 Ohms) with a tap in the middle or two windings of 20 volts (25 volts with a load of 8 Ohms) with a load current of up to 4 amperes. The diode bridge must meet the following requirements: forward current of at least 20 amperes and reverse voltage of at least 100 volts. The diode bridge can be successfully replaced with four rectifier diodes with the corresponding indicators.
Electrolytic filter capacitors C3 and C4 are designed mainly to remove the peak load of the amplifier and eliminate voltage ripple coming from the rectifier bridge. These capacitors have a capacity of 10,000 microfarads with an operating voltage of at least 50 volts. Non-polar capacitors (film) C1 and C2 can have a capacity of 0.5 to 4 µF with a supply voltage of at least 50 volts.
Voltage distortions should not be allowed; the voltage in both arms of the rectifier must be equal.
(1.2 Mb, downloaded: 4,057)
Author of the article: Novik P.E.
Introduction
Designing an amplifier has always been a challenging task. Fortunately, recently, many integrated solutions have appeared that make life easier for amateur designers. I, too, did not complicate the task for myself and chose the simplest, high-quality, with a small number of parts, does not require configuration and stable operation of the amplifier 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 excites if the wiring is incorrect; it burns for any reason, etc.” Nothing like this. It can only be burned by improper switching on or short circuiting, and cases of excitation have never been noticed, and not just by me. In addition, it has internal protection against short circuits in the load and protection against overheating. It also includes a muting function (used to prevent clicking when turned on) and a standby function (when there is no signal). This IC is a class AB ULF. 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 with a resistance of 4 Ohms), the ability to operate in a wide range of supply voltages, high technical characteristics (low distortion, low noise, wide range of operating frequencies, 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 range | 3db signal Output power 1W |
20-20000 | Hz | ||
| Long-term output power (RMS) | harmonic coefficient 0.5%: Up = ± 35 V, Rн = 8 Ohm Up = ± 31 V, Rн = 6 Ohm Up = ± 27 V, Rн = 4 Ohm |
60 60 60 |
70 70 70 |
W | |
| Peak music output power (RMS), duration 1 sec. | harmonic factor 10%: Up = ± 38 V, Rн = 8 Ohm Up = ± 33 V, Rн = 6 Ohm Up = ± 29 V, Rн = 4 Ohm |
100 100 100 |
W | ||
| Total harmonic distortion | Po = 5W; 1kHz Po = 0.1-50W; 20-20000Hz |
0,005 |
0,1 |
% | |
| Up = ± 27 V, Rн = 4 Ohm: Po = 5W; 1kHz Po = 0.1-50W; 20-20000Hz |
0,01 |
% | |||
| Protection response temperature | 145 | 0 C | |||
| Quiescent current | 20 | 30 | 60 | mA | |
| Input impedance | 100 | kOhm | |||
| Voltage Gain | 24 | 30 | 40 | dB | |
| Peak output current | 10 | A | |||
| Operating temperature range | 0 | 70 | 0 C | ||
| Case thermal resistance | 1,5 | 0 C/W | |||
(PDF format).
There are quite a lot of circuits for connecting this microcircuit, I will consider the simplest one:
Typical connection diagram:
List of elements:
| Position | Name | Type | Quantity |
| C1 | 0.47 µF | K73-17 | 1 |
| C2, C4, C5, C10 | 22 µF x 50 V | K50-35 | 4 |
| C3 | 100 pF | 1 | |
| C6, C7 | 220 µF x 50 V | K50-35 | 2 |
| C8, C9 | 0.1 µF | 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 >600 cm2. Be careful, on the microcircuit body there is not a common one, but a power minus! When installing the microcircuit on a radiator, it is better to use thermal paste. It is advisable to place a dielectric (mica, for example) between the microcircuit and the radiator. The first time I didn’t attach any importance to this, I thought, why would I be so frightened that I would short the radiator to the case, but in the process of debugging the design, tweezers that accidentally fell from the table shorted the radiator to the case. The explosion was awesome! The microcircuits were simply blown to pieces! In general, I got off with a slight fright and $10 :). On the board with the amplifier, it is also advisable to supply powerful electrolytes 10,000 microns x 50V, so that during power peaks the wires from the power supply do not cause voltage dips. 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 butter.” Capacitor C3 can be removed (or not installed), which is what I did. As it turned out, it was precisely because of it that when a volume control (a simple variable resistor) was turned on in front of the amplifier, an RC circuit was obtained, which, when the volume increased, mowed down the high frequencies, but in general it was needed to prevent excitation of the amplifier when ultrasound was applied to the input. Instead of C6, C7, I put 10000mk x 50V on the board, C8, C9 can be installed of any similar value - these are power filters, they can be in the power supply, or you can solder them by surface mounting, which is what I did.
Pay:
I personally don’t really like using ready-made boards, for one simple reason - it’s difficult to find elements exactly the same size. But in an amplifier, the wiring can greatly affect the sound quality, so it's up to you to decide which board to choose. Since I assembled an amplifier for 5-6 channels at once, therefore the board for 3 channels at once:
In vector format (Corel Draw 12)
Amplifier power supply, low pass filter, etc.
power unit
For some reason, the amplifier's power supply raises many questions. In fact, right here, everything is quite simple. A transformer, diode bridge and capacitors are the main elements of the power supply. This is enough to assemble the simplest power supply.
To power a power amplifier, voltage stabilization is not important, but the capacitance of the power supply capacitors is important, the larger the better. The thickness of the wires from the power supply to the amplifier is also important.
My power supply is implemented according to the following scheme:
The +-15V power supply is intended to power operational amplifiers in the amplifier's preliminary stages. You can do without additional windings and diode bridges by powering the stabilization module from 40V, but the stabilizer will have to suppress a very large voltage drop, which will lead to significant heating of the stabilizer microcircuits. Stabilizer chips 7805/7905 are imported analogues of our KREN.
Variations of blocks A1 and A2 are possible:
Block A1 is a filter for suppressing power supply noise.
Block A2 is a block of stabilized voltages +-15V. The first alternative option is easy to implement, for powering low-current sources, the second is a high-quality stabilizer, but requires precise selection of components (resistors), otherwise you will get a misalignment of the “+” and “-” arms, which will then result in a zero misalignment on the operational amplifiers.
Transformer
The power supply transformer for a 100W stereo amplifier should be approximately 200W. Since I was making an amplifier for 5 channels, I needed a more powerful transformer. But I didn’t need to pump out all 100W, and all channels cannot simultaneously draw power. I came across a TESLA transformer on the market (below in the photo) 250 watts - 4 windings of 1.5 mm wire of 17V each and 4 windings of 6.3V each. By connecting them in series, I got the required voltages, although I had to rewind the two 17V windings a little in order to get the total voltage of the two windings ~27-30V, since the windings were on top - it wasn’t too difficult.
An excellent thing is a toroidal transformer, these are used to power halogen lamps, there are plenty of them in markets and stores. If two such transformers are structurally placed one on top of the other, the radiation will be mutually compensated, which will reduce interference to 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 cost a lot. In principle, you can buy 2 transformers for 100-150 Watt 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 I made a separate bridge for each arm to provide a current reserve for the diodes. When turned on, powerful capacitors are charged, and 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, 20 A across two arms. In this case, the transformer and rectifier diodes operate briefly in short circuit mode. Current breakdown of diodes will have unpleasant consequences. The diodes were installed on the radiators, but I did not detect heating of the diodes themselves - the radiators were cold. To eliminate power supply interference, it is recommended to install a ~0.33 µF capacitor, type K73-17, in parallel with each diode in the bridge. I really didn't do this. In the +-15V circuit, you can use bridges of the KTs405 type, for a current of 1-2A.
Design
Ready design.
The most boring activity is the body. For the 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 in a separate compartment and you can freely put 3 more amplification channels into the case.
After field tests, it turned out that it would be useful to install fans to blow over the radiators, despite the fact that the radiators are quite 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 100 Ohm trimmer resistor 1 W at the lowest speed (see next figure).
Amplifier block
The microcircuits are based on mica and thermal paste, the screws also need to be insulated. 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 it was all temporary....
After hanging these guts, a slight hum appeared in the speakers, apparently something was wrong with the “ground”. I dream of the day when I throw it all out of the amp and use it only as a power amp.
Adder board, low pass filter, phase shifter
Regulation block
Result
It turned out more beautiful from the back, even if you turned it butt forward... :)
Construction cost.
| TDA 7294 | $25,00 |
| capacitors (power electrolytes) | $15,00 |
| capacitors (others) | $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, it didn't come cheap. Most likely I didn’t take something into account, I just bought, as always, much more of everything, because I still had to experiment, and I burned 2 microcircuits and exploded one powerful electrolyte (I didn’t take all this into account). This is a calculation for an amplifier for 5 channels. As you can see, the radiators turned out to be very expensive; I used inexpensive but massive processor coolers; 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 may wonder whether you need it :), although it contains an amplifier of a lower quality. Amplifiers of this class cost about $500.
List of radioelements
| Designation | Type | Denomination | Quantity | Note | Shop | My notepad |
|---|---|---|---|---|---|---|
| DA1 | Audio amplifier | TDA7294 | 1 | To notepad | ||
| C1 | Capacitor | 0.47 µF | 1 | K73-17 | To notepad | |
| C2, C4, C5, C10 | 22 µF x 50 V | 4 | K50-35 | To notepad | ||
| C3 | Capacitor | 100 pF | 1 | To notepad | ||
| C6, C7 | Electrolytic capacitor | 220 µF x 50 V | 2 | K50-35 | To notepad | |
| C8, C9 | Capacitor | 0.1 µF | 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 |
BM2033
LF amplifier 100 W (TDA7294, ready-made unit)
1463 rub.
The proposed unit is a reliable, powerful low-frequency amplifier with small dimensions, a minimum number of external passive wiring elements, and a wide range of supply voltages and load resistances. The amplifier can be used both outdoors and indoors as part of your musical audio complex. The amplifier has proven itself well as a ULF for a subwoofer.
Attention! This amplifier requires a BIPOLARY power supply and, if you plan to use it in a car from a battery, then in this case you will need TWO BATTERIES or one battery together with the NM1025.
| Parameter | Meaning |
| Upit. constant BIPOLARY, V | ±10...40 |
| Upit. nom. constant BIPOLARY, V | ±40 |
| Iconsumption Max. at Upit. nom. | 100 W / 36 V = 2.5 A |
| Irest, mA | 60 |
| Recommended AC Power Supply not included | transformer with two secondary windings TTP-250 + diode bridge KBU8M+ ECAP 1000/50V (2 pcs.), or two S-100F-24 power supplies (not for maximum power) or NT606 (not for maximum power) |
| Recommended radiator, not included. The radiator size is sufficient if during operation, the element installed on it does not heat up more than 70 °C (if touched by hand - tolerable) |
205AB0500B, 205AB1000B 205AB1500B, 150AB1500MB Install through the KPTD insulator! |
| Operating mode | AB class |
| Uin., V | 0,25...1,0 |
| Uin.nom., V | 0,25 |
| Rin., kOhm | 100 |
| Rload, Ohm | 4... |
| Rload.nom., Ohm | 4 |
| Rmax. at Kgarm.=10%, W | 1 x 100 (4 Ohm, ±29 V), 1 x 100 (6 Ohm, ±33 V), 1 x 100 (8 Ohm, ±38 V) |
| UMZCH chip type | TDA7294 |
| frab., Hz | 20...20 000 |
| Dynamic range, dB | |
| Efficiency at f=1kHz, Pnom. | |
| Signal/noise, dB | |
| Short circuit protection | Yes |
| Overcurrent protection | |
| overheat protection | Yes |
| Overall dimensions, LxWxH, mm | 43 x 33 |
| Recommended Case not included | |
| Operating temperature, °C | 0...+55 |
| Relative operating humidity, % | ...55 |
| Production | Contract manufacturing in Russia |
| Warranty period | 12 months from date of purchase |
| Lifetime | 5 years |
| Weight, g |
The ULF is made on the TDA7294 integrated circuit. This IC is a class AB ULF. Thanks to a wide range of supply voltages and the ability to deliver current to a load of up to 10 A, the microcircuit provides the same maximum output power at loads from 4 Ohms to 8 Ohms. One of the main features of this microcircuit is the use of field-effect transistors in the preliminary and output amplification stages.
Structurally, the amplifier is made on a printed circuit board made of foil fiberglass. The design provides for installation of the board into the case; for this purpose, mounting holes along the edges of the board are reserved for 2.5 mm screws.
The amplifier chip must be installed on a heat sink (not included in the kit) with an area of at least 600 cm2. As a radiator, you can use the metal case or chassis of the device into which the ULF is installed. During installation, it is recommended to use heat-conducting paste type KTP-8 to increase the reliability of the IC.
To “softly” turn off the sound, leg 10 (MUTE) of the microcircuit is used.
To “softly” turn off the amplifier in Standby Mode, leg 9 (STAND-BY) of the microcircuit is used.
In this design, the amplifier uses simultaneous control of two modes (MUTE and STAND-BY).
SW1 open - sound on, amplifier on
SW1 is closed - MUTE - no sound, STAND-BY - standby mode
The amplifier operates when the voltage at leg 9 and leg 10 is greater than + 3.5 volts. Such levels allow you to control the amplifier from conventional digital microcircuits.
If the voltage at the corresponding pin is less than +1.5 volts relative to ground (in fact, relative to pin 1 connected to ground), then the mode is turned on - the microcircuit is silent, or completely disabled. If the voltage is greater than +3.5 V, then the mode is disabled.
A correctly assembled ULF does not require tuning. However, before using it, you need to do several operations:
1. Check the correct connection of the signal source, load and MUTE/ST-BY control signals (if the standard switch SW1 fails to be used).
2. Apply the supply voltage, the useful signal, and then close SW1 to start the chip.
The unit is configured and completely ready for use.
X1 - Entrance. Apply the signal here from the preamplifier, AUX output of the radio.
X2 - GND (common). Apply an amplified signal to X1, X2.
X3 - Connect the red positive +48V power wire
X4 - GND (common). Connect the green power wire (the middle connection point of single-pole power supplies).
X5 - Positive output "+" to the speaker.
X6 - Negative output "-" to the speaker. Attention: this is not -48V (not a minus bipolar power supply!) Connect a speaker to X5, X6.
X7 - Connect the black negative power wire -48V.
Electrical circuit diagram BM2033
Connection diagram BM2033 after the timbre block VM2111
Using BM2033 with NM1025
Information about the required bipolar power supply for the BM2033
As a stereo amplifier we We do not recommend using very powerful circuits that require bipolar power supply due to the lack of bipolar power supplies. If you have decided to buy a powerful amplifier BM2033 (1 x 100 W) or BM2042 (1 x 140 W), then this means that you are ready to buy powerful power supply, the cost of which may exceed the cost of the amplifier itself several times.
As a power source you can use IN3000S (+6...15V/3A), or IN5000S (+6...15V/5A), or PS-65-12 (+12V/5.2A), or PW1240UPS (+ 12V/4A), or PW1210PPS (+12V/10.5A), or LPS-100-13.5 (+13.5V/7.5A), or LPP-150-13.5 (+13.5V/11.2A).
Amplifiers BM2033 (1 x 100 W) and BM2042 (1 x 140 W) require bipolar power supply, which, unfortunately, we do not have in finished form. Alternatively, it can be provided series connected unipolar power supplies from the sources listed above. In this case, the cost of the power supply doubles.
Oddly enough, but for many users, problems begin already when purchasing a bipolar power supply or making it yourself. In this case, the two most common mistakes are often made:
- Use a single-supply power source
- When purchasing or manufacturing, take into account effective value of voltage of the secondary winding of the transformer, which is written on the transformer body and which is shown by the voltmeter when measuring.
Description of the bipolar power supply circuit for BM2033
1.1 Transformer- must have TWO SECONDARY WINDINGS. Or one secondary winding with a tap from the midpoint (very rare). So, if you have a transformer with two secondary windings, then they need to be connected as shown in the diagram. Those. the beginning of one winding with the end of another (the beginning of the winding is indicated by a black dot, this is shown in the diagram). Get it wrong and nothing will work. When both windings are connected, we check the voltage at points 1 and 2. If the voltage there is equal to the sum of the voltages of both windings, then you have connected everything correctly. The connection point of the two windings will be the “common” (ground, case, GND, call it what you want). This is the first common mistake, as we see: there should be two windings, not one.
Now the second error: The datasheet (technical description of the microcircuit) for the TDA7294 microcircuit states: +/-27 power is recommended for a 4 Ohm load. The mistake is that people often take a transformer with two 27V windings, THIS CAN'T BE DONE!!! When you buy a transformer, it says effective value, and the voltmeter also shows you the effective value. After the voltage is rectified, it charges the capacitors. And they are already charging before amplitude value which is 1.41 (root of 2) times greater than the current value. Therefore, in order for the microcircuit to have a voltage of 27V, the transformer windings must be 20V (27 / 1.41 = 19.14 Since transformers are not made for such voltage, we will take the nearest one: 20V). I think the point is clear.
Now about the power: in order for the TDA to deliver its 70W, it needs a transformer with a power of at least 106W (the efficiency of the microcircuit is 66%), preferably more. For example, a 250W transformer is very suitable for a stereo amplifier on the TDA7294
1.2 Rectifier bridge- As a rule, questions do not arise here, but still. I personally prefer to install rectifier bridges, because... no need to bother with 4 diodes, it’s more convenient. The bridge must have the following characteristics: reverse voltage 100V, forward current 20A. We put up such a bridge and don’t worry that one “fine” day it will burn down. This bridge is enough for two microcircuits and the capacitor capacity in the power supply is 60"000 μF (when the capacitors are charged, a very high current passes through the bridge)
1.3 Capacitors- As you can see, the power supply circuit uses 2 types of capacitors: polar (electrolytic) and non-polar (film). Non-polar (C2, C3) are necessary to suppress RF interference. By capacity, set what will happen: from 0.33 µF to 4 µF. It is advisable to install our K73-17, which are pretty good capacitors. Polar (C4-C7) are necessary to suppress voltage ripple, and besides, they give up their energy during amplifier load peaks (when the transformer cannot provide the required current). Regarding capacity, people still argue about how much is needed. I learned from experience that for one microcircuit, 10,000 uF per arm is enough. Capacitor voltage: choose yourself, depending on the power supply. If you have a 20V transformer, then the rectified voltage will be 28.2V (20 x 1.41 = 28.2), capacitors can be set to 35V. It's the same with non-polar ones. It seems like I didn't miss anything...
As a result, we got a power supply containing 3 terminals: “+”, “-” and “common”. We’re done with the power supply, let’s move on to the microcircuit.
2) Chips TDA7294 and TDA7293
2.1.1 Description of the pins of the TDA7294 chip
1 - Signal ground
4 - Also a signal ground
5 - The pin is not used, you can safely break it off (the main thing is not to mix it up!!!)
7 - "+" power supply
8 - "-" power supply
11 - Not used
12 - Not used
13 - "+" power supply
14 - Chip output
15 - "-" power supply
2.1.2 Description of the pins of the TDA7293 chip
1 - Signal ground
2 - Inverse input of the microcircuit (in the standard circuit the OS is connected here)
3 - Non-inverted input of the microcircuit, we supply an audio signal here through the isolation capacitor C1
4 - Also a signal ground
5 - Clippmeter, basically an absolutely unnecessary function
6 - Voltage boost (Bootstrap)
7 - "+" power supply
8 - "-" power supply
9 - Conclusion St-By. Designed to put the microcircuit into standby mode (that is, roughly speaking, the amplifying part of the microcircuit is disconnected from the power supply)
10 - Mute output. Designed to attenuate the input signal (roughly speaking, the input of the microcircuit is turned off)
11 - Input of the final amplification stage (used when cascading TDA7293 microcircuits)
12 - The capacitor POS (C5) is connected here when the supply voltage exceeds +/-40V
13 - "+" power supply
14 - Chip output
15 - "-" power supply
2.2 Difference between TDA7293 and TDA7294 chips
Such questions come up all the time, so here are the main differences between the TDA7293:
- Possibility of parallel connection (complete garbage, you need a powerful amplifier - assemble it with transistors and you will be happy)
- Increased power (by a couple of tens of watts)
- Increased supply voltage (otherwise the previous point would not be relevant)
- They also seem to say that it is all made on field-effect transistors (what’s the point?)
That seems to be all the differences, I’ll just add that all TDA7293 have increased glitches - they light up too often.
- How to connect an LED to control the start-up of the VM2033 amplifier?
- The LED should be connected in parallel to any arm of the power source. Don't forget to install a current-limiting R=1 kOhm in series with the LED.
VM2033 is just a fairy tale! I used it to replace a burnt-out channel in the old Start 7235. It pumps 1.5-2 times more powerful than before, despite the fact that it heats up less. Now I want to use them to replace the terminals in Vega122. There was only one little thing that upset me - due to my carelessness, I screwed the microcircuit directly to the radiator. As a result, I had to resolder the microcircuit itself and restore the burnt out track.
Updated: 04/27/2016
An excellent amplifier for home can be assembled using the TDA7294 chip. If you are not strong in electronics, then such an amplifier is an ideal option; it does not require fine tuning and debugging like a transistor amplifier and is easy to build, unlike a tube amplifier.
The TDA7294 microcircuit has been in production for 20 years and has still not lost its relevance and is still in demand among radio amateurs. For a novice radio amateur, this article will be a good help in getting to know integrated audio amplifiers.
In this article I will try to describe in detail the design of the amplifier on the TDA7294. I will focus on a stereo amplifier assembled according to the usual circuit (1 microcircuit per channel) and will briefly talk about the bridge circuit (2 microcircuits per channel).
TDA7294 chip and its features
TDA7294 is the brainchild of SGS-THOMSON Microelectronics, this chip is an AB class low-frequency amplifier, and is built on field-effect transistors.
The advantages of the TDA7294 include the following:
- output power, with distortion 0.3–0.8%:
- 70 W for 4 ohm load, conventional circuit;
- 120 W for 8 ohm load, bridge circuit;
- Mute function and Stand-By function;
- low noise level, low distortion, frequency range 20–20000 Hz, wide operating voltage range - ±10–40 V.
Specifications
| Technical characteristics of the TDA7294 chip | |||||
|---|---|---|---|---|---|
| Parameter | Conditions | Minimum | Typical | Maximum | Units |
| Supply voltage | ±10 | ±40 | IN | ||
| Frequency range | Signal 3 db Output power 1W |
20-20000 | Hz | ||
| Long-term output power (RMS) | harmonic coefficient 0.5%: Up = ±35 V, Rн = 8 Ohm Up = ±31 V, Rн = 6 Ohm Up = ±27 V, Rн = 4 Ohm |
60 60 60 |
70 70 70 |
W | |
| Peak music output power (RMS), duration 1 sec. | harmonic factor 10%: Up = ±38 V, Rн = 8 Ohm Up = ±33 V, Rн = 6 Ohm Up = ±29 V, Rн = 4 Ohm |
100 100 100 |
W | ||
| Total harmonic distortion | Po = 5W; 1kHz Po = 0.1–50W; 20–20000Hz |
0,005 | 0,1 | % | |
| Up = ±27 V, Rн = 4 Ohm: Po = 5W; 1kHz Po = 0.1–50W; 20–20000Hz |
0,01 | 0,1 | % | ||
| Protection response temperature | 145 | °C | |||
| Quiescent current | 20 | 30 | 60 | mA | |
| Input impedance | 100 | kOhm | |||
| Voltage Gain | 24 | 30 | 40 | dB | |
| Peak output current | 10 | A | |||
| Operating temperature range | 0 | 70 | °C | ||
| Case thermal resistance | 1,5 | °C/W | |||
Pin assignment
| Pin assignment of the TDA7294 chip | |||
|---|---|---|---|
| IC output | Designation | Purpose | Connection |
| 1 | Stby-GND | "Signal Ground" | "General" |
| 2 | In- | Inverting input | Feedback |
| 3 | In+ | Non-inverting input | Audio input via coupling capacitor |
| 4 | In+Mute | "Signal Ground" | "General" |
| 5 | N.C. | Not used | – |
| 6 | Bootstrap | "Voltage boost" | Capacitor |
| 7 | +Vs | Input stage power supply (+) | |
| 8 | -Vs | Input stage power supply (-) | |
| 9 | Stby | Standby mode | Control block |
| 10 | Mute | Mute mode | |
| 11 | N.C. | Not used | – |
| 12 | N.C. | Not used | – |
| 13 | +PwVs | Output stage power supply (+) | Positive terminal (+) of the power supply |
| 14 | Out | Exit | Audio output |
| 15 | -PwVs | Output stage power supply (-) | Negative terminal (-) of the power supply |
Note. The microcircuit body is connected to the power supply negative (pins 8 and 15). Do not forget about insulating the radiator from the amplifier body or insulating the microcircuit from the radiator by installing it through a thermal pad.
I would also like to note that in my circuit (as well as in the datasheet) there is no separation of input and output lands. Therefore, in the description and in the diagram, the definitions of “general”, “ground”, “housing”, GND should be perceived as concepts of the same sense.
The difference is in the cases
The TDA7294 chip is available in two types - V (vertical) and HS (horizontal). The TDA7294V, having a classic vertical body design, was the first to roll off the production line and is still the most common and affordable.
Complex of protections
The TDA7294 chip has a number of protections:
- protection against power surges;
- protection of the output stage from short circuit or overload;
- thermal protection. When the microcircuit heats up to 145 °C, the mute mode is activated, and at 150 °C the standby mode is activated;
- protection of microcircuit pins from electrostatic discharges.
Power amplifier on TDA7294
A minimum of parts in the harness, a simple printed circuit board, patience and known good parts will allow you to easily assemble an inexpensive TDA7294 UMZCH with clear sound and good power for home use.
You can connect this amplifier directly to the line output of your computer sound card, because The nominal input voltage of the amplifier is 700 mV. And the nominal voltage level of the linear output of the sound card is regulated within 0.7–2 V.
Amplifier block diagram
The diagram shows a version of a stereo amplifier. The structure of the amplifier using a bridge circuit is similar - there are also two boards with TDA7294.
- A0. power unit
- A1. Control unit for Mute and Stand-By modes
- A2. UMZCH (left channel)
- A3. UMZCH (right channel)
Pay attention to the connection of the blocks. Improper wiring inside the amplifier may cause additional interference. To minimize noise as much as possible, follow several rules:
- Power must be supplied to each amplifier board using a separate harness.
- The power wires must be twisted into a braid (harness). This will compensate for the magnetic fields created by the current flowing through the conductors. We take three wires (“+”, “-”, “Common”) and weave them into a pigtail with a slight tension.
- Avoid ground loops. This is a situation where a common conductor, connecting blocks, forms a closed circuit (loop). The connection of the common wire must go in series from the input connectors to the volume control, from it to the UMZCH board and then to the output connectors. It is advisable to use connectors isolated from the housing. And for input circuits there are also shielded and insulated wires.
List of parts for TDA7294 power supply:
When purchasing a transformer, please note that the effective voltage value is written on it - U D, and by measuring it with a voltmeter you will also see the effective value. At the output after the rectifier bridge, the capacitors are charged to the amplitude voltage - U A. The amplitude and effective voltages are related by the following relationship:
U A = 1.41 × U D
According to the characteristics of the TDA7294, for a load with a resistance of 4 Ohms, the optimal supply voltage is ±27 volts (U A). The output power at this voltage will be 70 W. This is the optimal power for the TDA7294 - the distortion level will be 0.3–0.8%. There is no point in increasing the power supply to increase power because... the level of distortion increases like an avalanche (see graph).
We calculate the required voltage of each secondary winding of the transformer:
U D = 27 ÷ 1.41 ≈ 19 V
I have a transformer with two secondary windings, with a voltage of 20 volts on each winding. Therefore, in the diagram I designated the power terminals as ± 28 V.
To obtain 70 W per channel, taking into account the efficiency of the microcircuit of 66%, we calculate the power of the transformer:
P = 70 ÷ 0.66 ≈ 106 VA
Accordingly, for two TDA7294 this is 212 VA. The nearest standard transformer, with a margin, will be 250 VA.
It is appropriate to state here that the power of the transformer is calculated for a pure sinusoidal signal; corrections are possible for a real musical sound. So, Igor Rogov claims that for a 50 W amplifier, a 60 VA transformer will be sufficient.
The high-voltage part of the power supply (before the transformer) is assembled on a 35x20 mm printed circuit board; it can also be mounted:
The low-voltage part (A0 according to the structural diagram) is assembled on a 115x45 mm printed circuit board:
All amplifier boards are available in one.
This power supply for the TDA7294 is designed for two chips. For a larger number of microcircuits, you will have to replace the diode bridge and increase the capacitor capacity, which will entail a change in the dimensions of the board.
Control unit for Mute and Stand-By modes
The TDA7294 chip has a Stand-By mode and a Mute mode. These functions are controlled through pins 9 and 10, respectively. The modes will be enabled as long as there is no voltage on these pins or it is less than +1.5 V. To “wake up” the microcircuit, it is enough to apply a voltage greater than +3.5 V to pins 9 and 10.
To simultaneously control all UMZCH boards (especially important for bridge circuits) and save radio components, there is a reason to assemble a separate control unit (A1 according to the block diagram):
Parts list for control box:
- Diode (VD1). 1N4001 or similar.
- Capacitors (C1, C2). Polar electrolytic, domestic K50-35 or imported, 47 uF 25 V.
- Resistors (R1–R4). Ordinary low-power ones.
The printed circuit board of the block has dimensions of 35×32 mm:
The control unit's task is to ensure silent switching on and off of the amplifier using the Stand-By and Mute modes.
The operating principle is as follows. When the amplifier is turned on, along with the capacitors of the power supply, capacitor C2 of the control unit is also charged. Once it is charged, Stand-By mode will turn off. It takes a little longer for capacitor C1 to charge, so Mute mode will turn off second.
When the amplifier is disconnected from the network, capacitor C1 discharges first through diode VD1 and turns on the Mute mode. Then capacitor C2 discharges and sets the Stand-By mode. The microcircuit becomes silent when the power supply capacitors have a charge of about 12 volts, so no clicks or other sounds are heard.
Amplifier based on TDA7294 according to the usual circuit
The microcircuit's connection circuit is non-inverting, the concept corresponds to the original one from the datasheet, only the component values have been changed to improve the sound characteristics.
Parts List:
- Capacitors:
- C1. Film, 0.33–1 µF.
- C2, C3. Electrolytic, 100-470 µF 50 V.
- C4, C5. Film, 0.68 µF 63 V.
- C6, C7. Electrolytic, 1000 µF 50 V.
- Resistors:
- R1. Variable dual with linear characteristic.
- R2–R4. Ordinary low-power ones.
Resistor R1 is double because stereo amplifier. Resistance of no more than 50 kOhm with a linear rather than logarithmic characteristic for smooth volume control.
Circuit R2C1 is a high-pass filter (HPF) that suppresses frequencies below 7 Hz without passing them to the amplifier input. Resistors R2 and R4 must be equal to ensure stable operation of the amplifier.
Resistors R3 and R4 organize a negative feedback circuit (NFC) and set the gain:
Ku = R4 ÷ R3 = 22 ÷ 0.68 ≈ 32 dB
According to the datasheet, the gain should be in the range of 24–40 dB. If it is less, the microcircuit will self-excite; if it is more, distortion will increase.
Capacitor C2 is involved in the OOS circuit; it is better to take one with a larger capacitance to reduce its effect on low frequencies. Capacitor C3 provides an increase in the supply voltage of the output stages of the microcircuit - “voltage boost”. Capacitors C4, C5 eliminate noise introduced by wires, and C6, C7 supplement the filter capacity of the power supply. All amplifier capacitors, except C1, must have a voltage reserve, so we take 50 V.
The amplifier's printed circuit board is single-sided, quite compact - 55x70 mm. When developing it, the goal was to separate the “ground” with a star, ensure versatility and at the same time maintain minimal dimensions. I think this is one of the smallest boards for TDA7294. This board is designed for installation of one microcircuit. For the stereo option, accordingly, you will need two boards. They can be installed side by side or one above the other like mine. I’ll tell you more about versatility a little later.
The radiator, as you can see, is indicated on one board, and the second, similar one, is attached to it from above. Photos will be a little further.
Amplifier based on TDA7294 using a bridge circuit
A bridge circuit is a pairing of two conventional amplifiers with some adjustments. This circuit solution is designed for connecting acoustics with a resistance of not 4, but 8 ohms! Acoustics are connected between the amplifier outputs.
There are only two differences from the usual scheme:
- the input capacitor C1 of the second amplifier is connected to ground;
- added feedback resistor (R5).
The printed circuit board is also a combination of amplifiers according to the usual circuit. Board size – 110×70 mm.
Universal board for TDA7294
As you have already noticed, the above boards are essentially the same. The following version of the printed circuit board fully confirms the versatility. On this board you can assemble a 2x70 W stereo amplifier (regular circuit) or a 1x120 W mono amplifier (bridged). Board size – 110×70 mm.
Note. To use this board in a bridge version, you need to install resistor R5 and install jumper S1 in a horizontal position. In the figure, these elements are shown as dotted lines.
For a conventional circuit, resistor R5 is not needed, and the jumper must be installed in a vertical position.
Assembly and adjustment
Assembling the amplifier will not pose any particular difficulties. The amplifier does not require any adjustment as such and will work immediately, provided that everything is assembled correctly and the microcircuit is not defective.
Before first use:
- Make sure the radio components are installed correctly.
- Check that the power wires are connected correctly, do not forget that on my amplifier board the ground is not centered between plus and minus, but on the edge.
- Make sure that the microcircuits are isolated from the radiator; if not, then check that the radiator is not in contact with ground.
- Apply power to each amplifier in turn, so there is a chance you won’t burn out all the TDA7294 at once.
First start:
- We do not connect the load (acoustics).
- We connect the amplifier inputs to ground (connect X1 with X2 on the amplifier board).
- We serve food. If everything is fine with the fuses in the power supply and nothing smokes, then the launch was a success.
- Using a multimeter, we check the absence of direct and alternating voltage at the output of the amplifier. A slight constant voltage is allowed, no more than ±0.05 volts.
- Turn off the power and check the chip body for heating. Be careful, the capacitors in the power supply take a long time to discharge.
- We send a sound signal through a variable resistor (R1 according to the diagram). Turn on the amplifier. The sound should appear with a slight delay, and disappear immediately when turned off; this characterizes the operation of the control unit (A1).
Conclusion
I hope this article will help you build a high-quality amplifier using the TDA7294. Finally, I present a few photos of the assembly process, do not pay attention to the quality of the board, the old PCB is unevenly etched. Based on the assembly results, some edits were made, so the boards in the .lay file are slightly different from the boards in the photographs.
The amplifier was made for a good friend, he came up with and implemented such an original housing. Photos of the assembled stereo amplifier on the TDA7294:
On a note: All printed circuit boards are collected in one file. To switch between “signatures”, click on the tabs as shown in the figure.
list of files
TDA7294 (SGS-THOMSON MICROELECTRONICS)- in essence, this is a ready-made Hi-Fi ULF class AB with field-effect transistors in the input and output stages. The amplifier input sensitivity is 700mV. The circuit is the simplest, but nevertheless has high technical characteristics (see table below).
And this is a typical connection diagram for the TDA7294 microcircuit and a list of additional elements:
On some forums you come across unflattering reviews about the TDA7294, saying that the microcircuit gets excited or burns out altogether. Don’t pay attention to such statements, if everything is assembled correctly, the circuit works perfectly, there is no excitement, but it can burn out for one reason, the circuit was assembled with crooked hands, the power was supplied to the wrong place, or something was accidentally short-circuited. If installed correctly, it is difficult to burn out the microcircuit, it has internal protection against short circuits in the load, temperature protection is triggered when the microcircuit reaches 145 degrees, the presence of a muting function prevents clicks when the amplifier is turned on, there is a standby mode when there is no signal.
For the manufacture of a printed circuit board, single-sided fiberglass is used. The figure below shows a view from the side of the elements and their denominations are labeled:
Please note that filter capacitors C6, C7, C8, C9 in this version are installed in the power supply, and not on the main board of the amplifier.
In general, of course, many radio amateurs design a printed circuit board depending on the dimensions of the existing elements; mainly the electrolytic capacitors used, with the same capacity, can differ significantly in size from each other. Below we present another option for printing on two channels, maybe it will be useful to someone.
Power supply for amplifier based on TDA7294.
As you already understand, the amplifier is powered from a bipolar source. Before you start designing a power supply, you need to decide what load the amplifier will operate on, i.e. 4 or 8 Ohm. For a load of 8 Ohms the optimal voltage will be +-35 volts, for 4 Ohms +-27 volts. This means that the transformer in the first case should have two windings of 25 volts each, in the second - two windings of 20 volts. You can roughly estimate the value of the variable and what will happen after the rectifier bridge with filter capacitors using the formula: Ua = 1.41xUd, where Ua is the amplitude value, Ud - effective. For example, from a 20 volt variable after the rectifier we get: 20*1.41=28.2 volts.
In terms of transformer power: to power two channels of the amplifier, a TS-250 from an old TV was rewound, the diameter of the secondary winding wire was calculated for a current of 5 amperes.
Read the article about calculating transformers:
See the following figure for the power supply diagram:
The +-15 volt auxiliary voltage is designed to power the preamp circuitry and can be adjusted to suit your needs.
As rectifier bridges, it is convenient to use diode assemblies designed for a current of about 20 amperes, because when the amplifier is turned on, high-capacity capacitors begin to charge, and the current surge is quite significant.
Do not forget to install the microcircuits on radiators of at least 600 cm2. And keep in mind that the body of this mikruhi is not a common wire, but a minus of the power supply, therefore, use KPT paste and mica to isolate it from the radiator. For cooling, some use radiators from computer processors with an additional fan installed on it (see figure below)
The easy repeatability of the amplifier is due to the not too expensive TDA7294 microcircuit, a small number of additional elements and the simplicity of the circuit. If everything is done carefully and correctly, then there is nothing special to adjust, the amplifier works and the ear is happy.
Addendum to the article:
You can download the amplifier circuit board for the TDA7294 in LAY format using a direct link from our website. File size - 26 KB.
