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100 Watt Audio Power Amplifier

This is an exceptionally well designed amplifier, with a lot of power reserve, high fidelity, low distortion, good S/N ratio, high sensitivity, low consumption and full protection. Having all these almost ideal characteristics this amplifier is likely to become the basic building block of your future high fidelity system, or it can also become the element that will upgrade your existing system.

How it Works

The circuit works from a symmetrical ñ 40 VDC power supply and draws a maximum current of 2.6 A. The input circuit of the amplifier is a differential amplifier built around Q4 and Q5 that employ DC feedback thus preventing any DC voltage from appearing across the speaker with the usual destructive results. Q11 acts as a current source and ensures that the input stage draws a constant current of 1 mA.

The signal which appears as a voltage drop across the resistor connected in series with the collector of Q4 is used to drive the DARLINGTON pair Q3, Q2 which together with the constant current source of 7 mA that is Q10, form the driver stage. This stage operates in class A and is driving the complementary output stage Q1, Q9. The transistor Q7 is used to balance the circuit at different temperatures and must be mounted on the heatsink between the out put transistors. The feedback loop which consists of R8, R9, C2, C3 provides AC stability to the circuit. The circuit also incorporates a protection stage that makes it virtually indestructible. This protection circuit is built around Q6, Q8. If for whatever reason the output remains connected on one supply rail and the common the output is also protected from high DC voltages that could burn the speakers. The supply rails should be protected by 2 A fuses for the 8 ohm version and 3 A for the 4 ohm.

Technical Specifications - Characteristics

Output power (f=1 KHz, d=0.5 %): 100 W in 8 ohm
Supply voltage: ................  40 V
Quiescent current: ............. 50 mA
Maximum current: ............... 2.6 A
Sensitivity: . 600 mV
Frequency response: ............ 10-35000 Hz (-1 dB)
Distortion HD: ................. 0.01 %
Intermodulation dist.: ......... 0.02 %
Signal/noise: 83 dBConstruction


To cater for those who wish to use 4 ohm speakers with this amplifier the Kit includes the necessary components for both versions. The components that differ are R3,4,17 and 23. If you build the 8 ohm version then you must also include in the circuit R28 and D7, D8 which are not used in the 4 ohm version. As you see all the components are already marked on the component side of the p.c. board.

The construction is made this way much simpler. Start the construction from the pins and the jumper connections, continue with the resistors and the capacitors and last solder in place the semiconductors. Check each resistor before soldering it, to see if its colours match those in the component list. Be careful with the electrolytic capacitors because their polarity should be respected. The polarity of those capacitors is marked on their bodies and on the component side of the p.c. board.

NOTE: On the p.c. board next to R2, R16 are marked two other resistors which do not appear in the circuit diagram but are included in the components. They are of 1 ohm 2 W (brown, black, gold) and must be included in the circuit. Take care when you are soldering the semiconductors because if you overheat them they can be damaged.

The output transistors should be mounted on the heatsink that is included in the kit. Take care not to short circuit them with the heatsink and we recommend that you use some HTC between the transistor body and the sink in order to improve heat dissipation. Follow the diagram for the mounting of the power transistors as it shows clearly how to insert the insulators and the screws. Q7 should be made to touch the heatsink and is a good idea to use a bit of HTC between its casing and the surface of the heatsink.

When you finish the construction of your project clean the board thoroughly with a solvent to remove all flux residues and make a careful visual inspection to make sure there are no mistakes, components missing and short circuits across adjacent tracks on the board. If everything is OK you can make the following connections: Input: 3 (signal), 5 (common) Output: 7 (signal), 6 (common) Supply: 1 (-40 VDC), 2 (+40 VDC) 5 (0 VDC)

Connect a milliammeter in series with the power supply, short the input of the amplifier, turn the power ON and adjust the trimmer P1 so that the quiescent current is about 50 mA. When you finish this adjustment remove the shunt from the input and connect the output of a preamplifier to it. Connect the pre amplifier to a suitable source and turn everything ON.

The signal should be heard from the speakers clear and undistorted. First of all let us consider a few basics in building electronic circuits on a printed circuit board. The board is made of a thin insulating

material clad with a thin layer of conductive copper that is shaped in such a way as to form the necessary conductors between the various components of the circuit. The use of a properly designed printed circuit board is very desirable as it speeds construction up considerably and reduces the possibility of making errors. Smart Kit boards also come pre-drilled and with the outline of the components and their identification printed on the component side to make construction easier. To protect the board during storage from oxidation and assure it gets to you in perfect condition the copper is tinned during manufacturing and covered with a special varnish that protects it from getting oxidised and makes soldering easier. Soldering the components to the board is the only way to build your circuit and from the way you do it depends greatly your success or failure. This work is not very difficult and if you stick to a few rules you should have no problems. The soldering iron that you use must be light and its power should not exceed the 25 Watts. The tip should be fine and must be kept clean at all times. For this purpose come very handy specially made sponges that are kept wet and from time to time you can wipe the hot tip on them to remove all the residues that tend to accumulate on it.
 DO NOT file or sandpaper a dirty or worn out tip. If the tip cannot be cleaned, replace it. There are many different types of solder in the market and you should choose a good quality one that contains the necessary flux in its core, to assure a perfect joint every time.
DO NOT use soldering flux apart from that which is already included in your solder. Too much flux can cause many problems and is one of the main causes of circuit malfunction. If nevertheless you have to use extra flux, as it is the case when you have to tin copper wires, clean it very thoroughly after you finish your work. In order to solder a component correctly you should do the following:

  • Clean the component leads with a small piece of emery paper. - Bend them at the correct distance from the component body and insert the component in its place on the board.

  • You may find sometimes a component with heavier gauge leads than usual, that are too thick to enter in the holes of the p.c. board. In this case use a mini drill to enlarge the holes slightly. Do not make the holes too large as this is going to make soldering difficult afterwards.

  • Take the hot iron and place its tip on the component lead while holding the end of the solder wire at the point where the lead emerges from the board. The iron tip must touch the lead slightly above the p.c. board.

  • When the solder starts to melt and flow, wait till it covers evenly the area around the hole and the flux boils and gets out from underneath the solder. The whole operation should not take more than 5 seconds. Remove the iron and leave the solder to cool naturally without blowing on it or moving the component. If everything was done properly the surface of the joint must have a bright metallic finish and its edges should be smoothly ended on the component lead and the board track. If the solder looks dull, cracked, or has the shape of a blob then you have made a dry joint and you should remove the solder (with a pump, or a solder wick) and redo it.

  • Take care not to overheat the tracks as it is very easy to lift them from the board and break them.

  • When you are soldering a sensitive component it is good practice to hold the lead from the component side of the board with a pair of long-nose pliers to divert any heat that could possibly damage the component.

  • Make sure that you do not use more solder than it is necessary as you are running the risk of short-circuiting adjacent tracks on the board, especially if they are very close together.

  • When you finish your work cut off the excess of the component leads and clean the board thoroughly with a suitable solvent to remove all flux residues that still remain on it.
If it does not work

Check your work for possible dry joints, bridges across adjacent tracks or soldering flux residues that usually cause problems. Check again all the external connections to and from the circuit to see if there is a mistake there.

  • See that there are no components missing or inserted in the wrong places.

  • Make sure that all the polarised components have been soldered the right way round. - Make sure the supply has the correct voltage and is connected the right way round to your circuit.

  • Check your project for faulty or damaged components. If everything checks and your project still fails to work, please contact your retailer and the Smart Kit Service will repair it for you.

L1 : 10 turns with wire 0,5mm turned on a restistor of 1W

If you use a 4Ohm speaker you will place R3,4,17,23 at the board.

If you use a 8Ohm speaker you will place D7 D8 and R28.

For R2 and R16 if you don't find a 0,47Ohm place two of 1 Ohm parallel.

R16 must be 0,47Ohm...the 1Ohm must be a typographical error, take care of this, i haven't tested it.

Compact High-Performance 12V 20W Stereo Amplifier

Amplifiers which run from 12V DC generally don’t put out much power and they are usually not hifi as well. But this little stereo amplifier ticks the power and low distortion boxes. With a 14.4V supply, it will deliver 20 watts per channel into 4-ohm loads at clipping while harmonic distortion at lower power levels is typically less than 0.03%.

This is an ideal project for anyone wanting a compact stereo amplifier that can run from a 12V battery. It could be just the ticket for buskers who want a small but gutsy amplifier which will run from an SLA battery or it could used anywhere that 12V DC is available – in cars, recreational vehicles, remote houses with 12V DC power or where ever.

12 Volt 20W Stereo Amplifier circuit schematic

Because it runs from DC, it will be an ideal beginner’s or schoolie’s project, with no 240VAC power supply to worry about. You can run it from a 12V battery or a DC plugpack. But while it may be compact and simple to build, there is no need to apologise for “just average” performance. In listening tests from a range of compact discs, we were very impressed with the sound quality.

Long-time readers might recall that we presented a similar 12V power amplifier design back in May 2001. It was a similar configuration to this one but it is now completely over-shadowed by the much lower distortion and greatly improved signal-to-noise ratio of this new design. In fact, let’s be honest: the previous unit is not a patch on this new design. It used two TDA1519A ICs which resulted in distortion figures above 1% virtually across the board and a signal-to-noise ratio of only -69dB unweighted.

20W Stereo Amplifier circuit schematic

However, by using the TDA­7377 power amplifier IC and making some other improvements, the THD (total harmonic distortion) of the new design is about 50 times better than the older unit (see performance graphs for details). The bottom line is that the THD under typical conditions is around just 0.03% or less. It is also able to deliver more output power due to the improved output transistors in the new power amplifier IC.

In addition, its idle power consumption is low – not much more than 1W. As a result, if you don’t push it too hard it will run cool and won’t drain the battery too quickly. And because the IC has self-protection circuitry, it’s just about indestructible. It will self-limit or shut down if it overheats and the outputs are deactivated if they are shorted.

Circuit diagram:
12V 20W Stereo Amplifier circuit schematic

With a 12V supply, the largest voltage swing a conventional solid-state power amplifier can generate is ±6V. This results in a meagre 4.5W RMS into 4O and 2.25W RMS into 8O, without considering losses in the output transistors. Even if the DC supply is around 14.4V (the maximum that can normally be expected from a 12V car battery), that only brings the power figures up to 6.48W and 3.24W for 4O and 8O loads respectively – still not really enough.

There are three common solutions to this problem. The first is to boost the supply voltage using a switchmode DC converter. This greatly increases the cost and complexity of the amplifier but it is one way of getting a lot of power from a 12V supply. However, we wanted to keep this project simple and that rules out this technique.

Parts layout:
PCB layout of compact 12V 20W Stereo Amplifier circuit schematic

There are variations on the boosting method, such as the class H architecture used in the TDA1562Q IC featured in the Portapal PA Amplifier (SILICON CHIP, February 2003). It is able to achieve 40W/channel but with >0.1% THD. In that case, the amplifier output itself provides the switching for a charge pump. The second method is to lower the speaker impedance. Some car speakers have an impedance as low as 2O, which allows twice as much power to be delivered at the same supply voltage. However, we don’t want to restrict this amplifier to 2O loudspeakers.
Author: Nicholas Vinen - Copyright: Silicon Chip

Identify IC TDA7293 and TDA7294 Fake or Original

TDA7293 and TDA7294 is a common feature of the bootstrap capacitor is not installed work as usual, which gives an opportunity for unscrupulous traders to provide fake, counterfeit goods market is the most polished printed for the TDA7294 TDA7293, from the printing on the can identify, find a few different batches of IC for your reference:

If you can not see it, multimeter test:
TDA7294 pin 11, pin 12 empty legs, open state is insulated
TDA7293 pin 11 (voltage amplification stage output), pin 12 (bootstrap) has a resistance:

图片点击可在新窗口打开查看Picture this subject as follows: 3456 +1. Gif
TDA7293 limit voltage 120v
Limit voltage 100v TDA7294
I found that some batches were TDA7294 90V breakdown in the type of IC sound like TDA2030, reaction was slow, boring sound, though not sure whether the fake, but certainly not a good thing!
The breakdown is not more than 90V, the general performance of the midrange and treble sound clear and bright, fast response! Found in different batches of test and origin of the TDA7294 sound even different!
Sound quality not as good as Legend TDA7293 TDA7294, wrong! I found a few pieces of genuine TDA7293 sample tests and found TDA7293 TDA7294 sound much better than that, the biggest feature is bright! Fast! Power foot.
Above are for reference only, are welcome to share and talk about their experiences

TDA7293 + upc1237 Integrated Amplifier with Speaker Protection Circuit

TDA7293 + upc1237 integrated amplifier speaker protection circuit board,with Morocco genuine IC, clear and transparent sound quality!
Audio channel, "European "style, all with Philips capacitors:decoupling filtering using Philips C 470uf/50v audio capacitors, Philips 0.1uf, 100V MKT, input capacitance Philips 1uf/250V MKP (better than MKT ! less waste!) bootstrap capacitor: PhilipsPHILIPS22uf/100V audio capacitor, negative feedback DC blocking capacitors Philips 22uf/100V, full-bridge 25A1000V (15A is sufficient), filter capacitor 12000uF 2 only (measured). Coupling, bootstrap, negative feedback DC-blocking capacitors were installed before the match, reduced errors, more accurate positioning to pan!

Circuit real materials, design science will have good sound, small volume whenthe soft and delicatetenderness allows you to enjoy a "European style"! Alt bursting bright when you'll likely getloud!

Circuit design features:
1:relay protection circuit can not be omitted!A speaker a few hundred dollars, and an IC tens of dollars!Switch which is no current impact sound amplifier fever minimum requirement!
2: Integrated rectifier, horn protection, power amplifier into one, convenient!
3: The filter capacitor is measured using instruments elected, the board adopted Sanyoung12000UF50WV, all of the measured capacity is greater than 10000uF, to ensure bursting with power! (Lot of brands on the market are sets of skin capacitance, renovation, disassemble parts, simply by the instrument that pays top academics ... a lot of testing capacity is only half! Filter capacitor also instruments speak for themselves!)
4: Audio channel system used in Europe and Philips MKT Philips electrolytic capacitor decoupling, resolving power better! The protection circuit uses Japanese-made capacitors do not waste resources and
5:1% of the audio channels all use metal film resistors;input capacitance with MKP. The face of hundreds of high-power operational amplifier K resistance, input capacitance, although little effect on MKP psychological effect or to vote for it!
6: The most critical is the choice of high-power amplifier TDA7293IC, you may not believe that a model with the quality of different batches of the IC 369 will be divided and so on, but I tested a few batches of the TDA7293, even sound different! In order not to touch the interests of some business, do not say. OUR engineer "winnowed out" some good batches of IC on Taobao only for your reference!

Recognition of experience TDA7293/7294 Post:

Is limited, I hope you valuable advice!

TDA7293ICbasic parameters:
Power: 140W +140 W
Output Impedance :4-8 ohms
Harmonic Distortion: 0.005%
Input voltage :24-30V dual AC input (recommended).
Board body size: 14 X 7.8 X 6 dimensions (cm)

Note: IC such as TDA7293 or TDA7294 heat sink and the negative power of its similarities to install the radiator and IC must be isolated from insulation, thermal conductivity recommended mica and particles, buying power amplifier board shop and complimentary high-quality mica particles

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