Many people may have heard of the TDA2822 before, but for those who haven't, it is a small power amplifier that will drive two channels. It is usually in an 8-pin DIL package, but older versions I have seen are 14-pin or similar (there are datasheets for both variants). For simplicity though, my circuits show schematics for the 8-pin DIL package. The datasheet is here, provided by ST. This article is based along the usage of the TDA2822M variant of the chip series as it is commonly available at my supplier at least. The TDA2822 is similar, but has slightly more pins so is less used.
A Few Interesting points:
I have seen the TDA2822 used in commercial offerings too, based on a circuit very similar to the schematic shown. An old ghetto Blaster used this chip (the 14-pin version) and for a small old system, its performance is better than many cheap offerings today. I have also seen this chip in use in PC speakers, a pair I got free when I brought a computer case claimed 120W PMPO. Well I won't lie like they do, this amp is only capable of 700mW per channel from a 6V power supply into 8 ohms (should be over a watt with 12V). This amp can also function well as an amp for headphones, providing 20mW into 32 ohms from 3V. I would have used it for that purpose in my main system, but unfortunately, space was limited and all I could do was run some resistors in series with the output to cut down the volume for headphones.
So what have I done with these amps then? Well recently I have rebuilt a pair of speakers I had to be amplified with this amp. The speakers are quite large 4in speakers, but the TDA2822M will provide over a watt into each from the 12V PSU I am using. With built in transformer, these speakers easily impress more then most cheap walkman and PC speakers.
I have changed my small stereo speakers from a two TDA7052 amps to one TDA2822M amp. This is because my TDA7052 circuit eventually failed. I guess this is so because the outputs from the TDA7052 are bridged and the removal and insertion of the 3.5mm plug that I used to connect the other speaker to the one with the amplifier circuit in would short the circuit momentary. The new circuit will make use of the TDA2822M's non-bridged output which is still capable of nearly as much power (enough for the reason I built the speakers).
The other amp I built was brought as a project kit and uses a similar circuit, the advantage of course was I didn't need to build the board. I used this amp in a small (ish) FM radio. Don't ask how I made a stereo FM radio circuit because the circuit was just re-used from a rather sorry ghetto Blaster. It does have LW and MW too, but these don't work properly. The speakers are just simple elliptical speakers, but quality is bad at all, although it needs a regulated PSU because that digital clock I put in makes the amp hum if it runs off the same unregulated PSU.
The circuit is simple to construct, it can be done easily on strip-board, although I have never tried it to be honest. As always make sure that you insert the TDA2822M chip in the board the right way and please get the electrolytic capacitors the right way round, I only recently blew one up in them larger speakers I have mentioned above. Nothing else is particularly critical, the amp will happily run with the cheapest resistor and capacitors you can buy. A dual log pot is recommended because it gives simple volume adjustment. Any thing else can be added as you require, i.e. tone controls etc, but it is unlikely you will need anything else for simple systems.
The circuit also contains a power LED, which can easily be removed if not needed by omitting R3 and LD1 and also includes a dual gang volume control in the form of RV1a and RV1b.
ST Microelectronics were nice enough to also provide PCB layouts in their datasheet. The following is the stereo application of the TDA2822M fit onto a very small sized board. The only problem with this is for most of my applications the TDA2822M has been a standalone amplifier PCB which means I have wanted to include both volume control, LED's and PCB jack and power sockets. I'm sure you can also modify the layout however to fit your needs...
Note: The above image is copied directly from the datasheet and is not mine, nor is it likely to be 1:1 scale. To achieve this scale, the best idea is to print to PDF file to A4 paper.
While this is mainly a battery operated device, a power supply is easy to make too, and a circuit idea is shown below. You shouldn't need more then 1000uF for the smoothing capacitor, although capacity more won't hurt, it will just increment your parts bill. A simple EI transformer is ideal for the job and 15VA will give you more then 1A with 9V secondary wirings.
MAINS VOLTAGE IS VERY DANGEROUS AND THE FOLLOWING PSU USES IT. DO NOT WIRE IT UNLESS YOU ARE SUITABLE QUALIFIED, DEATH OR SERIOUS INJURY MAY RESULT.
On the other hand, I would recommend, especially for beginners, that you just buy a simple DC adapter (giving about 12V). This is already made and rectified, and most importantly, safe becausemains electricity is dangerous. Get one with a good current output though, I would say 100mA is the absolute minimum, although this amp runs off a 9V PP3 longer than you would expect. For those who want a bit more volume, get a 12V PSU which will provide 1A or more (although more is probably unnecessary), and connect speakers that are sensitive to it, like those elliptical speakers in my radio, or better. Small low cost speakers (especially 55mm or less) have low sensitivity, as do high quality hi-fi speakers and should be avoided unless they are necessary.
This amp can also be very portable, as before I built the radio, I used the amp in a small pair of Walkman type speakers (that were passive). Only from 3V, there was a lot more volume then having them just passive, I recall people were quite impressed (although as you can guess the tone from the speakers was poor).
Extra (simple) parts you may want to add to the schematic could be:
- 3.5mm jack input socket
- A power switch
- 2.1mm power plug (for external PSU's) - if wired correctly, this should disconnect the batteries when a plug is pushed into the socket.
There is a bridge variant of this chip available in the datasheet should it be required. It is smaller still then the stereo version of the chip and should provide output levels similar to or even greater then, the TDA7052.
Again, this circuit is simply taken from the datasheet and you may need to modify it to include a single gang volume control. Please refer to the datasheet for schematics, components their values.
That's about all that can be said about this amp because so many applications are possible from it - it is very cheap too, however if you want that extra power, using two TDA7052 amps is also simple and will give you a little more power. Remember that the TDA7052 amplifiers are bridged and may not be suitable for some situations.