There are quite a few varieties of budget amplifiers and this is one of them. The circuit is very simple and contains only one microcircuit, several resistors and capacitors. The characteristics of the amplifier are quite serious, at such a low cost. The output power reaches 100W at maximum power. Absolutely pure output is 70 W.
Amplifier Specifications
More detailed characteristics of the amplifier on the TDA7294:- The power supply is bipolar with a midpoint of 12 to 40 V.
- F out - 20-20000 Hz
- R out. Max. (supply +-40V, Rn=8 Ohm) - 100 W.
- R out. Max. (supply +-35V, Rn=4 Ohm) - 100 W.
- To the harmonics (Pout = 0.7 R max.) - 0.1%.
- Uin - 700 mV.
These amplifiers work great in pairs, so make two of these and you'll have a simple stereo amplifier. More detailed characteristics of the amplifier and switching circuits can be found in.
It is advisable to choose a power supply for the amplifier that is one and a half times more powerful, so keep this in mind.
Amplifier PCB
Drawing of the arrangement of elements:
Download to the board in lay format:
(downloads: 1084)
When printing, set the scale to 70%.
Ready amplifier
The microcircuit must be installed on a radiator, preferably with a fan, since it will be smaller in size. Making a printed circuit board is not at all necessary. You can take a breadboard with a large number of holes and assemble the amplifier in 30 minutes.
I advise you to build such a simple amplifier that has proven itself very well.
power unit
The power supply is completed according to the classical scheme with a 150 W transformer. I recommend taking a transformer with a ring core, since it is more powerful, smaller and emits a minimum of network interference and electromagnetic background of alternating voltage. The filter capacitors of each arm are 10,000 µF.Collect your amplifier and see you soon!
Due to its excellent technical characteristics, the presented amplifier is recommended for working with home electro-acoustic Hi-Fi equipment.
Its design uses TDA7294 integrated circuits manufactured by SGS-THOMPSON. In their structure, they have protection against short circuits in the load from overheating, as well as a noise reduction system.
Amplifier specifications:
- input impedance 22 kOhm;
- reproduced frequency band 20 Hz-100 kHz;
- output power constant 70 W/8 Ohm;
- musical power 100 W/8 Ohm (IIv. +/- 40 V).
Schematic diagram
The input signal is fed to the amplifier input through capacitor C1 and a low-pass filter consisting of resistor R1 and capacitor C2. Resistor R4 introduces negative feedback. The "MUTT" and "STANDBY" circuits that the amplifier is equipped with are automatically turned on after turning on the power.
Rice. 1. Schematic diagram of a powerful ULF on the TDA7294 chip (100 W).
If it becomes necessary to change the time constant of these circuits, the values of capacitors C9 and CJ should be selected accordingly. It is not recommended to reduce the values of resistors R5 and R6, as this may lead to exceeding the maximum permissible input current for the "MUNF" and "STANDBY" inputs.
Parts and installation
Built-in thermal protection turns off the amplifier when the circuit temperature rises above 145 °C. Installing the amplifier should not be difficult. Assembly should begin by soldering all the jumpers. Then you need to solder resistors and capacitors.
Integrated circuits must first be attached to heatsinks and then soldered onto the board. This will prevent the solder points from accidentally coming off.
The heatsinks that need to be used in the amplifier must provide adequate heat dissipation from the integrated circuits, otherwise they will turn off.
To fully utilize the capabilities of the amplifier, it should be equipped with a good power supply. It is best to use a 300 W toroidal transformer and a 2 x 10000 uF capacitor bank. You can also use two transformers with a power of 150 W each and install separate power supplies for each channel.
| US1 | TDA7294 |
| C1 | 1 µF |
| C2 | 2.2 nF |
| NW | 22 µF/16 V |
| C4, C7 | 100 nF |
| C8 | 22 µF/40 V |
| C4, C5 | 1000 µF/40 V |
| S9, S10 | 10 µF/35 V |
| R1 | 450 Ohm |
| R2, R4, R5, R6 | 22 kOhm |
| R3 | 680 Ohm |
The voltage supplying the amplifier can be within the range of +/-10-+/- 40 V. In any case, the voltage should not exceed 40 V, as this threatens to damage expensive integrated circuits.
When turning on the amplifier, it is necessary to connect a resistor with a power of several watts and a resistance of several tens of ohms in series with the power supply, which will protect the integrated circuits in case of short circuits on the board.
The quiescent current of the amplifier when powered with a voltage of +/-40 V should not be more than 60 mA. The DC output voltage of integrated circuits, measured relative to ground, must be 0 V.
This power amplifier is based on the PA100, described in detail in the application from National Semiconductor's AN1192
When I assembled my powerful homemade 4-ohm speakers, the amplifier could not “drive” such a load, so it was decided to assemble a more powerful amplifier. I have designed a power amplifier circuit that uses two LM3886s per channel in a parallel circuit. At an 8-ohm load, the output power of the amplifier is about 50 Watts, at a 4-ohm load it is 100 Watts. This amplifier uses four LM3886 ULF chips.
By the way, Jeff Rowland uses the LM3886 in some of his Hi-Fi designs and has good reviews. So an inexpensive amplifier can also be of high quality!
The LM3886 chip is connected as a non-inverting amplifier. The input impedance of the ULF depends on resistor R1 (47 kOhm). Resistor R20 (680 Ohms) and capacitor C20 (470 pF) form a high-pass filter on the RCA input connectors. Capacitors C4 and C8 (220 pF) are used to filter RF at the inputs of the LM3886 chip.
When assembling the amplifier, in some places I used high-quality capacitors: C1 (1 µF) "Auricap" for DC filtering, C2 and C6 (100 µF) "Blackgate" and C12, C16 (1000 µF) "Blackgate".
The circuit diagram of the amplifier is shown below.
The development of the printed circuit board was carried out taking into account that the power ground (supply) and signal ground were separated. The signal ground is in the middle and is surrounded by the force ground. Near C5 they are connected by a thin path. The design of the printed circuit board was carried out in the PADS PowerPCB 5.0 program.
I didn’t make the printed circuit board myself, but gave it to a company. When I picked it up, I discovered that some of the holes were smaller in diameter than needed. I drilled it out myself by hand. The photo below is a photo of the board.
Resistors 1kOhm and 20kOhm were manually selected with an accuracy of 0.1%. As output resistors, I used six resistors with a nominal value of 1 Ohm 0.5 Watt 1%, because a 3 Watt 1% resistor is difficult to find.
I used an isolated version of the chip - LM3886 TF, so I directly connected it to the case and heatsink through thermal paste.
Isolation capacitor "Auricap" 1uF 450V. A high quality capacitor was purchased because it is involved in the main signal circuit.
Capacitors in the high-pass filter: "Silver Mica" 47pF and 220pF.
The power filter used a "Blackgate" 1000uF 50V capacitor
Condensers C2 and C6 are also from Blackgate with a nominal value of 100 µF 50 V. For best results, it is better to use bipolar capacitors, but I used electrolytes because... bipolar ones would not fit on the board.
The filter chain R20 (680 Ohm) + C20 (470 pF) is placed directly on the RCA connector. This helps filter out RF noise before it reaches the amplifier board.
The 0.1uF power supply coupling capacitor is soldered on the back of the amplifier board directly to the LM3886 leg, this allows for better filtering of RF noise.
The LM3886 chip is mounted on an aluminum radiator, and then to the amplifier body. Outside the case I attached 3 more radiators from PC processor fans. Thermal paste was used throughout for better heat transfer.
With all these heatsinks, the amplifier heats up quite a bit at medium volume.
In the power supply I used an LT1083 adjustable voltage regulator IC. In front of it I placed capacitors with a capacity of 10,000 μF and after - 100 μF. The advantage of using an adjustable voltage stabilizer is that there is virtually no ripple voltage. Without it, a small 50/100 Hz noise is heard.
Powerful MUR860 diodes were used in the diode bridges.
The LT1083 voltage stabilizer can provide current up to 8A.
The transformer was used with a power of 500VA 2x25V. After the stabilizer, the voltage is 30 Volts.
In the future I plan to replace the stabilizer with a more powerful one (see diagram below). The TIP2955 transistor is capable of withstanding currents up to 15A.
After assembling the amplifier, I measured the DC voltage and found an offset of about 7 mV at the speaker terminals. The voltage difference between the two outputs of the microcircuits is less than 1 mV.
The sound of the amplifier is somewhat similar to the sound of the amplifier I previously assembled on the LM3875 - very clean. There is no noise, no hissing, no buzzing. Compared to the LM3875 amp, this amp delivers about twice the power through my 4 ohm speakers and delivers deep, punchy bass and good dynamics.
List of radioelements
| Designation | Type | Denomination | Quantity | Note | Shop | My notepad | |
|---|---|---|---|---|---|---|---|
| ULF | |||||||
| U1, U2 | Audio amplifier | LM3886 | 2 | To notepad | |||
| C1 | Capacitor | 1 µF | 1 | To notepad | |||
| C2, C6 | 100 µF | 2 | To notepad | ||||
| C3, C7 | Capacitor | 4.7 pF | 2 | To notepad | |||
| C4, C8 | Capacitor | 220 pF | 2 | To notepad | |||
| C5, C9 | Electrolytic capacitor | 10 µF | 2 | To notepad | |||
| C10, C11, C13 | Capacitor | 0.1 µF | 3 | To notepad | |||
| C12, C14 | Electrolytic capacitor | 1000 µF | 2 | To notepad | |||
| C20 | Capacitor | 470 pF | 1 | To notepad | |||
| R1 | Resistor | 47 kOhm | 1 | To notepad | |||
| R2, R3, R7, R8 | Resistor | 1 kOhm | 4 | To notepad | |||
| R4, R9 | Resistor | 22 kOhm | 2 | To notepad | |||
| R5, R10 | Resistor | 10 kOhm | 1 | To notepad | |||
| R6, R11, R13-R16 | Resistor | 0.5Ohm 1W 1% | 6 | To notepad | |||
| R12 | Resistor | 2 ohm | 1 | To notepad | |||
| R20 | Resistor | 680 Ohm | 1 | To notepad | |||
| power unit | |||||||
| U1, U2 | Linear regulator | LT1083 | 2 | To notepad | |||
| D1-D8 | Rectifier diode | MUR860 | 8 | To notepad | |||
| C1, C4 | Electrolytic capacitor | 10000 µF | 2 | To notepad | |||
| C2, C5 | Capacitor | 1 µF | 2 | To notepad | |||
| C3, C6 | Electrolytic capacitor | 100 µF | 2 | To notepad | |||
| R1, R2 | Resistor | 100 Ohm | 2 | To notepad | |||
| R3, R4 | Trimmer resistor | 2.5 kOhm | 2 | To notepad | |||
| TX1, TX2 | Transformer | 220/25V | 2 | To notepad | |||
| Powerful stabilizer | |||||||
| N1, N2 | Linear regulator | LM317 | 2 | To notepad | |||
| V1, V2 | Bipolar transistor | TIP2955 | 2 | To notepad | |||
| V3-V12 | Rectifier diode | MUR1560 | 10 | To notepad | |||
| V13, V14 | Rectifier diode | 1N4007 | 2 | ||||
This is a repeatedly tested circuit of a homemade 100-watt amplifier based on the popular TDA7294 microcircuit, reinforced with a pair of powerful output transistors. This circuit is intended for a low-resistance load, but in it most of the output current is not removed from the microcircuit, but is supplied to the load by additional transistors. And the microcircuit only controls them. UMZCH is designed to work with low-impedance loads with a power of 100 watts or more.
As you can see, the amplifier on the TDA7294 MS is complemented by two powerful output transistors operating in B mode. They amplify the output current of the microcircuit, so much less power is dissipated on it, which is why you can raise the supply voltage to get increased power in the load. At rest, the output transistors are closed and do not consume current from the power source. At a low signal level (up to ~0.5 volts at the load), the transistors do not open, and the output signal flows from the output of the microcircuit to the load through resistor R7. At the same time, tension appears on it. As the signal level increases, the voltage on R7 increases, and when it reaches ~0.6 volts (this corresponds to a power of 30...50 mW at a 4 Ohm load), the output transistors begin to open. At low output voltages, the output transistors open only at volume peaks for a short time. As the output signal increases, the output stage is switched on, taking over power for the load. In this case, only 10% of the power flows from the microcircuit to the speaker and another ~10% of the output power is spent by the microcircuit on driving the output transistors.
Thus, you can work on a low-impedance load and get the maximum voltage and current without overheating the microcircuit. Unlike “parallel” connection, here the microcircuit acts as a preliminary stage, and the main power is controlled by additional transistors. This connection would be a good option for boosting a powerful subwoofer, with its power reaching up to 100 W. A more powerful microcircuit easily provides such power. The second option is the low-frequency/mid-frequency channel of a two-way amplifier (the high-frequency channel is made on a TDA7294 without amplification) for sounding the room. Only bipolar transistors can be used as outputs! For field ones, to open, you need to apply a lot of voltage - about 4 volts, or even more. And this voltage is formed across resistor R7. Its power should be at least 5 W, it will heat up accordingly. And, most importantly, only one microcircuit without outputs will work at low power.
Coil L1 can be wound directly onto R8. To do this, take a resistor of the MLT-2 W type and wind 2 layers of wire with a diameter of 1 mm around it. The top layer should be shorter so that the coils do not slip. Lightly soak the coil with glue to prevent it from coming apart. We wind the coil leads onto the resistor leads. The chip will need a small heatsink. You can put it and the transistors on a common radiator through gaskets. After assembling the amplifier, you need to make sure that there is no self-excitation by looking at the signal using an oscilloscope.
To increase the output power of the amplifier over 100 watts, it is necessary to raise the supply voltage of the transistors to 50 volts with an unstabilized voltage. And for the microcircuit we use a stabilizer for +- 38 volts. The stabilizer is connected to breaks in the power supply circuits of the microcircuit at points A and B. Now power supply voltage drops do not affect the microcircuit, so the power supply to the microcircuit is always maximum and it can always produce the maximum output voltage. This means that the voltage and power at the load will always be the maximum possible.
TDA7294- low-frequency amplifier microcircuit produced by the French company THOMSON. This microcircuit is built on field-effect transistors, which ensures high sound quality, and a minimum of external elements guarantees good repeatability of the device. A correctly assembled amplifier from serviceable parts begins to work immediately and does not require adjustment. The appearance of the microcircuit is shown in the first figure.
To assemble an amplifier on the TDA7294 you will need the following parts:
1. Chip TDA7294 (or TDA7293)
2. Resistors with a power of 0.25 watt
R1 - 680 Ohm
R2, R3, R4 - 22 kOm
R5 - 10 kOhm
R6 - 47 kOm
R7 - 15 kOhm
3. Film capacitor, polypropylene:
C1 - 0.74 mkF
4. Electrolytic capacitors:
C2, C3, C4 - 22 mkF 50 volt
C5 - 47 mkF 50 volt
5. Double variable resistor - 50 kOm
For a stereo amplifier you will need a double set of parts, with the exception of the variable resistor.
The installation is made on a printed circuit board made of single-sided foil fiberglass. Its drawing is presented in the second picture. An archive with the board in .cdr format on a one-to-one scale has also been added.
A microcircuit is installed on the board, from which unused pins have been removed: 5, 11 and 12. Install using a wire with a cross-section of at least 0.74 mm2. The chip itself must be installed on a radiator with an area of at least 600 cm2. The radiator should not touch the amplifier body in such a way as there will be a negative supply voltage on it. The housing itself must be connected to a common wire.
Now a few words about the power supply.
The power supply is a step-down transformer with two windings with a voltage of 25 volts and a current of 5 amperes. It is better to use ultra-fast diodes in the rectifier, but in principle ordinary ones will do. It is advisable to solder a capacitor with a capacity of 0.01 mkF in parallel to each diode. Filter capacitors C1 and C3 have a capacity of 22,000 mkF at a voltage of 50 volts, capacitors C2 and C4 have a capacity of 0.1 mkF. Pay special attention to the power supply, the voltage on the windings should be the same and the filter capacitors too. Voltage imbalance should not be allowed. When power is supplied to the amplifier, it must be supplied at the same time. Otherwise, the chip will explode, which is very impressive!
The supply voltage of 35 volts should only be with a load of 8 ohms; if you have a load of 4 ohms, then the supply voltage should be reduced to 27 volts. In this case, the voltage on the secondary windings of the transformer should be 20 volts.
You can download the printed circuit board files for this amplifier circuit on the TDA7294 chip.
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Source: http://bezkz.su
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