Contents

Warning: These chips has been discontinued and are susceptible to fakes. If you're buying, make sure it is from a good supplier to get a genuine chip otherwise performance will be bad, the chip may be easily damaged and create a hazard, or hum/buzz/hiss may be worse than the official chip, or it may just not work at all.

The original TDA7056 chip is very hard to find and expensive if you do - I've not been able to obtain and test it myself. The TDA7056A and TDA7056B chips are easier to find but are not drop in replacements (despite commonly advertised without the A suffix by some sellers). These 'A' and 'B' variants are still cheap, and the circuit is still very simple. All chips should be made by Philips (now NXP). Note that the gain for the TDA7056A is different than the TDA7056 too.

If you can't get the TDA7056 or the TDA7056A/TDA7056B variants mentioned here, alternative include:

• TDA7266M supports the same 3V to 18V voltage output, is also bridged, and gives more power, however it needs a few more components. TDA7297 (stereo) and TDA7391LV (mono) are other alternatives, but 6V upwards only
• STA540 / TDA7375 are better alternatives still
• LM383 / TDA2003 are also obsolete alternatives, but may be easier to find

Recommended Experience : beginner

TDA7056 application

Quick facts TDA7056

• Power output: 3W into 16 ohms at 10% 1kHz distortion with power supply 11V
• Power output: 1W into 8 ohms at 10% 1kHz distortion with power supply 6V
• Gain: 40dB (fixed)
• Power supply: 3V to 18V single supply
• THD: 0.25%
• Peak output current repetitive: 1A
• Datasheet available here

Guide

The TDA7056 is essentially a slightly upgraded TDA7052 amplifier that is able to handle a bit more power, especially if given a heatsink. Just like the TDA7052, it maintains its simplicity. Largely, this article repeats much of the same information, but adjusted for specifics.

The chip is built by Philips Semiconductors and a data sheet is available here. The chip itself has two amplifiers inside it in bridge configuration to give a good power output for its size. The circuit shown in this data sheet is very simple indeed, requiring only two other components at its bare minimum.

The TDA7056 is a mono amplifier, however if you want stereo, you can either buy two TDA7056 chips, or look at the TDA7057Q, which is the stereo version.

My schematic below shows how simple the circuit is. I've also included a resistor to ensure the input impedance is predictable, a volume control using a 47k potentiometer and DC blocking capacitor C3 to stop the potentiometer becoming noisy over time due to DC in the audio input. They are not completely necessary, and my original schematic did not show them, but I recommend to keep them to avoid problems as they'll add very little cost and take only a small amount of extra room.

#	Type	Quantity
U1	TDA7056	1
R1	4k7 ohm Resistor, ¼W Metal Film, 1%	1
C1	100nF Capacitor, 50V+ Ceramic X7R or MLCC	1
C2	220µF Capacitor, 25V+ Electrolytic	1
In,Vdd,SPK	2.54mm header 2-pin	3
	Heatsink, cable, connectors	~

The capacitors C1 and C2 are for power supply decoupling and are considered necessary. C1 should be a 100nF (0.1µF) ceramic capacitor and located closest to the TDA7056 pins. C2 should be an electrolytic capacitor of 220µF or higher with a voltage rating of a few volts higher than your supply voltage (i.e., 10V for 6V supply, 16V for 12V supply, 25V for 15V supply).

Resistor R1 can be any 4k7 resistor which is 5% tolerance or better. Metal film resistors are best, however since the resistor is not directly in the signal path a cheap carbon resistor will also be fine.

A volume control is not shown but can be added easily at the input pin. It should be 47k linear as the linear potentiometer loaded with R1 will give a good logarithmic response. In order to stop it becoming noisy after time, a DC blocking capacitor of 10µF should be added in front of that. See the TDA7052 article for how to add VR1 and C3 in to the circuit - the same concept will work here.

Below is a layout for the amp for beginners using Veroboard or 'stripboard'. The layout is simple, but you will need to use a track cutter to cut three traces where the amplifier chip is soldered onto the board (shown by the orange squares) but be careful to leave the trace between pin 3 and pin 5 connected as this is where the two grounds meet. If your power and signal ground meet elsewhere in your system, you can also cut this trace in order to avoid ground loops.

The layout does not include a volume control (or capacitor before it) or any LED power indicator. If you have some understanding of electronic circuit design, then you can easily incorporate these onto the board. This will require additional wiring and/or track cutting for the preferred layout.

Construction

Soldering is required to fix the components to the board. If you're a beginner and have not done this before, by all means practice. Soldering on stripboard can be a little challenging at first as it is easy to short the adjacent tracks if too much solder is used. Once this is done, it is difficult to correct without desoldering braid or pump, so avoid using too much solder and touching the other tracks with the iron. I suggest having desolder braid handy as it really saves time to use it to mop up solder when you do make a mistake.

The TDA7056 chip will NOT tolerate lots of solder heat. Therefore, do each solder joint quickly and allow ample time for the chip to cool down before moving on to the next pin. Technically, you only need to solder 6 of the 9 pins as the other 3 are N.C. (no-connection), however, I suggest you solder them all to give the chip physical strength to the board, otherwise it may be too easy to flex and break the soldered legs or their joints to the board.

After soldering, use your continuity tester to ensure that adjacent tracks are not accidentally touching. You can also check the leads of most components to see if they are electrically connected to the stripboard tracks.

The 0.1µF (or 100nF) C1 is a ceramic capacitor. You'll need to spread the leads to bridge from pin 2 to pin 7. The 220µF capacitor C2 is an electrolytic capacitor, and it will also need lead bending/spreading to fit the same wide spacing. Don't worry if it does not fit flush to the board. THE CAPACITOR MUST BE CONNECTED THE RIGHT WAY ROUND, otherwise it's bubble, burst, or launch itself off the board, especially with higher voltages (i.e., 9-12V). On both the schematic and stripboard layout the positive side is shown. On the capacitor itself the negative lead is usually clearly labelled on the capacitor can, or if it's a new capacitor the positive lead is usually the longest lead.

The 4k7 resistor R1 is mounted vertically to avoid the need for an extra jumper if it was mounted horizontally. To mount it vertically, simply bend one end 180 degrees back on itself. The two lead ends should now easily fit in adjacent holes in the board. Vertically mounting resistors like this is often fine and I've seen it done in equipment too.

Once components are soldered and the excess leads have been trimmed, use one of the excess to make a bridge (jumper) between the GND and PGND tracks.

This amplifier is intended to power an 8 ohm speaker from a 6V power supply without a heatsink. With a heatsink, you can push it with a higher voltage for more power, but the datasheet contains no output information for such, I would not go beyond 12V. The maximum voltage of 18V is intended for higher impedance speakers such as 16 ohm and 32 ohm.

I do not recommend driving 4 ohm speakers with it, but if you do (and I have done), then keep the supply under 9V and ensure there is a heatsink.

When wiring the loudspeaker, do not ground it. The TDA7056 uses BTL (Bridge Tied Load) which gives you up to 4 times the power with two amps (which are integrated in the TDA7056) in to the same load impedance. If you short the loudspeaker to ground, do not expect it to work. It may not even protect itself from a repeated loudspeaker short condition.

As a last note, make sure you put the TDA7056 in the right way before you solder it. The stripboard layout shows an asterisk on the chip. This asterisk indicates pin 1, which is the first on the left when the labelled side of the chip faces you. The schematics are oriented so that pin 1 is the first on the left.

The TDA7056, whilst great, is not bullet proof, so avoid mistakes such as connecting the power supply the wrong way round, soldering the chip the wrong way round or shorting out the loudspeaker connections. To avoid this for loudspeaker connections, do not use 3.5mm style connections to the loudspeaker because they may briefly short it whilst inserting/removing whilst the amp is powered on. Use spring clips, banana plugs, DIN sockets or (since it's low power) phono and mini DIN sockets are also fine.

Power

The datasheet is brief on power details. It states 1W output for a 6V power supply into 8 ohms without a heatsink. With a heatsink, it should be possible to get around 2.5W of power off 12V, or even higher if the voltage is raised higher.

Given this is a single supply chip (positive and ground), there are many options for powering it.

8 1.5V AA cells (or UM-3, M, RX6) would give 12V of battery power, or a 7.4V lithium battery will work well.

Power through USB is also an option. USB gives 5V and most PC USB ports now are capable of supplying more than 1A of current, however even the standard 500mA USB current will get a single TDA7056 running fine. At 5V though you can only expect 1W of power at best and at this power, the TDA7056 will draw 400 to 500mA, so running a stereo pair may be a challenge.

If you are running at lower voltages though, the TDA7052 might be a cheaper and easier alternative.

The best power is available from a dedicated power supply.

Wall/brick power supplies are easy to find, and you may even have some unused ones laying around! Aim for 12V. These should have a rated output of 500mA or better for a single TDA7056. Double that for a stereo pair. I recommend increasing C2 to 1000µF to bypass and smooth the voltage further.

Gain

The gain is fixed and cannot be changed by changing/adding like many other amplifiers. The fixed gain of 40dB is rather high, representing a voltage gain of around 100 times! This is calculated as 10^(dB/20) = 10^(40/20) = 100.

Because of the high gain, noise performance won't be fantastic, and you may find that the volume control is rather sensitive if you use a potentiometer that has a low value or too high value.

TDA7056 Building a 'system'

The above schematic is the amplifier with a volume control and that may be all you need to integrate with an existing system. If you're building a new system though you may want to add extra components:

• A power switch
• A power LED
• A low pass filter to remove frequencies above 20kHz
• Batteries and/or
• A power supply
• Optional power supply filtering

The diagram above shows how you could build a mono system. S2 is the power switch, and LD1 with current limiting resistor R3 is a simple power LED using a small 3mm or 5mm LED of whatever colour you prefer.

J2 and S1 are part of a DC power jack. These jacks usually have three pins. One is positive, the other is negative. It's more common that the outside of DC barrel connectors is negative, so do double check! The third pin is usually connected to the barrel outside until you push a plug into the socket.

By connecting a battery box to the third pin, this means when there is no DC power plug pushed in the socket, the batteries are available, but when the DC power jack is pushed in, the batteries are disconnected. If the outside of the DC plug is negative, then that means you need to switch the negative side of the battery box.

L1 and C5 form a high pass filter that helps remove any audible whine noise from cheap switching power supplies. It won't completely eliminate noise, but it can help make what you have usable. You can exclude L1/C6 if you see no need for them, just replace L1 with a wire link. I suggest a value of 2.2µH to 10µH for L1. It should be able to handle at least 1A, preferably 1.5A or better. Power inductors that can easily handle this current should be easy to find at most electronic retailers.

On the input side, R2 and C4 form a low pass filter. The cut off frequency is about 34kHz which means frequencies above that will be attenuated. This helps with harmonics caused by GSM noise when your mobile rings or receives a message nearby.

All grounds must be connected to a single point star, bus or star of stars. Don't create loops or you'll get hum or whine noise when operating on mains powered equipment.

If you want to make a mono amplifier but have a stereo source (often the case), you will need to union the left and right channels as most material (music, TV etc.) will not sound its best or be complete when you only connect the left or right channel. You can do this by using two 1k or higher resistors as shown above (R2 and R4). To save components, the low pass filter can be combined with the summing resistors by dropping the value of C4 to 4.7nF.

A stereo system can be built almost as easily by duplicating the amplifier, speaker and input side components. In the schematic above, VR1 and VR2 should be a dual linear potentiometer so that turning it adjusts the volume to the same level for both left and right channels.

Performance

For the cost and simplicity, the TDA7056 is a pretty good solution to the portable, battery-operated amp problem. As it's a bigger chip that may have a heatsink attached, it's a next step up from the TDA7052 and other chips of the same size.

It's not hifi though, as evident from the 0.25% to 1% THD with just 0.5W of output power. It's not for car radios either, as the 1A peak current limit indicates that it will not be happy to drive 4 ohm speakers off a typical 14.4V.

TDA7056A and TDA7056B application

Quick facts TDA7056A

• Power output: 3W into 16 ohms at 10% 1kHz distortion with power supply 12V
• Gain: 35.5dB (variable via DC control) - max gain of 30dB in my application
• Power supply: 4.5V to 18V single supply
• THD: 0.3%
• Datasheet available here

Quick facts TDA7056B

• Power output: 3.5W into 16 ohms at 10% 1kHz distortion with power supply 12V
• Power output: 5.5W into 8 ohms at 10% 1kHz distortion with power supply 12V
• Gain: 40.5dB (variable via DC control) - max gain of 34dB in my application
• THD: 0.3%
• Power supply: 4.5V to 15V single supply
• Datasheet available here

Two variants of the TDA7056 that is more available nowadays are the TDA7056A and TDA7056B. They are very similar in terms of performance and pin out, but they will not work in the same circuit.

Of the two, the TDA7056B seems to be a little better in that the power output is slightly higher into 16 ohms, and this time, the datasheet actually gives a quoted power output of 5.5W into an 8 ohm speaker. This is the only chip I've brought and tested because it seems to be the best.

Comparing the circuit to the TDA7056, the TDA7056A/TDA7056B needs two additional components at minimum. This is because there is a DC volume control input which needs to be connected to ground via a 1µF capacitor. The input pin for the TDA7056A/TDA7056B (unlike the TDA7056) has a DC offset at its input pin too, meaning that a 470nF capacitor is also needed in series with the input and the input pin.

The extra components and larger board needed due to that is the disadvantage. The advantage is the DC volume control pin 5 provides us some flexibility over the basic TDA7056 above:

• The volume control potentiometer can now go directly to this dedicated pin
• The volume control input is logarithmic, and more accurate than a log potentiometer. This allows use of common linear potentiometers for volume control

Here's the adjusted schematic for a simple amplifier, with a sensible maximum gain of around 27dB for the TDA7056A, or 32dB for the TDA7056B:

#	Type	Quantity
U1	TDA7056A or TDA7056B	1
R1	4k7 ohm Resistor, ¼W Metal Film, 1%	1
R2	6.8k or 5.6k ohm Resistor, ¼W Metal Film, 1%	1
C1	100nF Capacitor, 50V+ Ceramic X7R or MLCC	1
C2	220µF Capacitor, 25V+ Electrolytic	1
C3,C4	1µF Capacitor, 16V+ Electrolytic	2
VR1	250k Lin Potentiometer	1
In,Vdd,SPK	2.54mm header 2-pin	3
	Heatsink, cable, connectors	~

Like the TDA7056, there are power supply bypass capacitors needed - C1 and C2. C1 should be a 100nF ceramic and as close to the TDA7056A pins as possible. C2 is an electrolytic capacitors of 220µF or higher. Electrolytic capacitors are polarised so the positive lead in must go in the positive voltage supply. This is the longest lead if the capacitor is new but check the casing anyway as the negative lead is usually clearly marked.

C3 is an input capacitor. 470nF is suggested in the datasheet and combined with the 20k input impedance this will give a high pass cutoff frequency of 16.93Hz - that's calculated by 1/(2πRC) - 1/(2 × 3.14159 × 20000 × 0.00000047).

C3 should be a polyester or electrolytic capacitor. Polyester is known to have the best audio quality but on an amplifier of this size you're unlikely to notice the difference and an electrolytic will be fine. Avoid a ceramic for this capacitor. If you have 1µF electrolytics, feel free to use those instead (that's what I did on my board). The positive lead must face the chip.

R1 provides a DC path to ground for the audio signal, and also gives the amplifier a predictable input impedance for whatever source you connect. This resistor is suggested as 5k in the datasheet but 4.7k is a more commonly available value that will work just as well.

Below is a layout for the amp for beginners using Veroboard or 'stripboard'. The layout is simple and needs no trace cuts. You will need to retain a lead offcut from one of the capacitor or resistors in order to make a jumper to connect the two ground pins together.

The volume control potentiometer itself I have not included on the board layout above as the size/shape will vary. See below for more details on the volume control. On my build though, I did include the volume control (layout below). To reduce the length, I also combined the input resistor and capacitor on the same PCB track as pin 1, but they need to be isolated by cutting the track where the orange square is.

DC volume control and gain

The DC volume control is at pin 5. The TDA7056A and TDA7056B produce a voltage of around +1.125V at this pin, as well using the current at this pin as a volume reference.

This VC pin gives a convenient way of adding a volume control that is accurate and will not go noisy over time.

Note: It is not possible to control multiple TDA7056A/TDA7056B chips with a single volume control by connecting the VC pins together. I've tried and unfortunately this just makes both chips distort. If you want a stereo amplifier, my first choice would be the TDA7057Q instead, which does allow you to connect the VC pins together, or alternatively just use a dual gang linear potentiometer with the 6k8 in series for each channel.

Capacitor C4 is a 1µF electrolytic that is used for power on muting. How this works is the capacitor initially looks like a short circuit, keeping the TDA7056A muted. The capacitor will then slowly charge by the 1.125 volts on pin 5, leaving the only path to ground via the resistor R2 and potentiometer VR1. For a longer mute time, you can increase the size of this capacitor.

The datasheet shows a 1M ohm potentiometer to allow control of the volume of up to 34dB. 34dB is a high gain, at over 50 times voltage gain, calculated as 10^(34/20). I actually measured nearly 57x (35dB) when I tried. A 220k potentiometer instead will give a gain of around 31dB (36x), which I found more suitable for plugging into laptops, phones, MP3 players etc.

If a gain of 31dB is too low (unlikely), with 500k I measured the gain to 51x (34dB) and that will still give better control compared to the 1M potentiometer.

The additional 6.8k resistor R2 in series with the potentiometer I added to avoid a 'dead' spot on the potentiometer where you have to turn it from its minimum a little more than expected before the TDA7056B has enough current to unmute itself. Feel free to leave this resistor out though if you wish. The gain measurements above include the 6k8 resistor in series with the potentiometer and with both 250k and 500k potentiometers the handling was good - allowing the amplifier to fully mute when the volume potentiometer is turned fully anti-clockwise, and only a small turn clockwise is needed from there to allow signal through.

If some signal is still coming through in your source though when the volume control is set to its minimum, reduce the value from 6k8 to 5k6 or maybe lower still.

The potentiometer is not shown on my layout, but it should be wired like this so that turning it clockwise turns the volume up. This is the front view:

The ground lead (first pin from the left) should be connected to input ground - either back to the board or your input socket.

To avoid noise when touching the potentiometer, consider grounding the metal casing of the pot too. This will not be needed if the potentiometer is mounted on a grounded metal case though, and you'll probably get away with not needing to ground the case either if you have a plastic knob on the potentiometer.

With no volume control connected (only the capacitor), the TDA7056B will still work with a gain of about 65x (36.2dB) from what I measured. If your volume control is elsewhere - you can consider leaving out any resistor and potentiometer from pin 5 completely or cap the gain to your preferred maximum using a fixed resistor e.g., 1M, 470k or 330k (1M giving the highest gain) from pin 5 to ground.

That's somewhat off the maximum possible gain quoted of 40.5dB 105x (typical). To get this gain maximum gain, you actually need to apply a voltage of 1.4V or higher to the VC pin 5. You could do this by connecting a resistor to the positive input, as suggested in the TDA7053A datasheet below. I suggest though that you don't wire the volume in this way unless you really need the maximum gain as the resistor needed will depend on your supply voltage and I prefer the flexibility of being able to plug the amplifier into whatever power supply is available.

Note that the TDA7056A has a different gain range (it's lower), the gains quoted above are for the TDA7056B but based on my experiments with a TDA7052A (which has similar gain) the maximum gain with no potentiometer or voltage source connected to VC will be about 37x (31.4dB).

I couldn't measure the voltage offset for these potentiometers as I found the voltage varied with/without a signal. The datasheet isn't great on details for the volume control, but it does show a gain vs voltage graph that gives you an idea of the voltages needed.

Being able to drive the volume with a DC offset voltage opens up the possibilities of actually driving the volume in other ways - such as with a microcontroller such as PIC or Arduino with a DAC chip, or just any digital potentiometer (does not need to be audio quality).

Power and performance

Below is my actual build. It only took less than 15 minutes to solder up. It's small, convenient, and works quite well. I also included the volume control on the board.

Performance/power is OK, and it could fit the need of a utility amplifier quite well. There are other amplifiers that outperform it now, especially some 25 years later, but this is still the amplifier requiring the least external components.

Your power supply should be in the region of 12V for driving an 8 ohm speaker. I found it could drive 4 ohms too, but it will get hotter still and voltage may need to be reduced below 7.5V to 6V.

Testing music seemed fine. Using a smartphone as a source via it's 3.5mm headphone output, I found it quite capable, and the 250k volume control potentiometer had a nice range to it.

Compared to the TDA7056, the TDA7056B needs a couple more components and a slightly bigger board but considering how quick and easy it was to build, and cheap it is to buy (including components), I think the TDA7056B still makes a great beginner project for building your own powered speaker.

For a stereo system, as mentioned, consider the TDA7057Q instead which will need less components, however you could use two TDA7056B chips using a similar technique as the stereo TDA7056 system above. You need a separate volume control on each chips VC pin, but this can be solved with a single dual gang potentiometer to control the volume of both amplifiers simultaneously.