TDA2040 - 20W single chip power amplifier

(plus TDA2050 notes)

The TDA2040 is a more powerful alternative to the TDA2030 mentioned in another article. It applications are similar, but here are the ideas again:

  • A pair can form a capable amp for a stereo system (i.e. a home made or upgraded midi system or 'ghetto-Blaster', although battery operation will not be possible).
  • This amplifier can be used to complete surround sound systems (i.e. centre and rear channel amps). I use this amp for my rear and centre channels in my current surround sound system.
  • A pair can be used to improve the sound from a NICAM® TV, or even one may be used to improve a mono TV.
  • Beefing up those 400W+ amps in PC speakers (seriously)!
  • Tweeter or mid range amplifiers in bi-amp or tri-amp systems.

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This amplifier is based on the typical application in the ST Microelectronics datasheet. The performance from this circuit is very satisfactory. The sheet contains data for typical noise and distortion statistics, I can't confirm these statistics because I don't have the equipment, but my ears tell me that the sound is good and with sensitive speakers, this amp will show quite a nice bit of power.

The circuit is even simpler than the one used for the TDA2030, yet the performance is even better. Again, you can try to make this amp on a veroboard or stripboard PCB, but you will have a hell of a job to mount the IC onto the board - I know I did! For those who do want to try, an illustration and description is below:

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It can be done, firstly I straightened out the pins, followed by cutting them to the length of the shortest two. Then VERY carefully, I split the pins apart so they would push into the pre-drilled holes in the stripboard - they do not need to go in far so do not force them further than necessary, the pins will break.

If your wiring onto PCB, then this is much simpler! Just layout the tracks in the way you prefer, drill the holes, etch it then solder in the small amount of components with minimal effort. The ST Microelectronics datasheet contains a suggested PCB layout which I used and this works well and is highly recommended.

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. 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.

Components

All resistors are recommend to be 1% metal film, but 5% will do (except for R4, the 4.7 ohm resistor). Capacitors should be electrolytic with values of 1uF or greater, although I used a tantalum capacitor - I would not recommend this though as the only benefit they bring are that they are smaller, mini-elects are available from my supplier anyway and they are barely bigger and much cheaper! All electrolytics should be rated at 25V minimum and be connected the right way round!...

That leads into a little story here, the first time I built the TDA2040 amp (on stripboard by the way) I made a mistake. Well I hooked up the amplifier with a music source, speaker and +/- 15V power supply. Excellent, everything was working so I decided to knock up the volume a bit, and then... an almighty BANG, with a flash of light and flames! It scared me a lot! When I returned to my senses, the amp was still working, with volume, but I took no chances and turned it off by whipping the mains plug out of the socket.

After looking, I realised that one of my capacitors had be reduced to its plastic base, C6 was that very one. Because I had worked with much smaller amplifiers with single rail supplies, I naturally put the negative side of the capacitor into ground. Of course when the positive goes into a -V rail, its obviously connected the wrong way round, and running 15V the wrong way through a capacitor is sure to make it violently explode. I then had the task of clearing up the mess made by the fluffy stuff that exploded from the capacitor. I did not find the top until a month later, behind my wardrobe. This means it accelerated upward, hit the ceiling and bounce behind the wardrobe - home-made rocket :O

On a more serious note, connect them the right way round, the possibilities of danger are high, a fire could start or the capacitor case could take out your eye, not pleasant. As for the other capacitors, these can be polyester types and they don't care what way round they go (fortunately)!

Back to the details... Do not run this amp without a good heatsink, it will get very hot very quickly and this shortens it life. Get a good heatsink for prolonged running, especially at high voltages into 4 ohms. It must also be insulated from the metal tab on the back on the chip. This usually means mica washers, but there are alternatives. Only if you are operating at low voltages can you get away with a small (medium-sized) plastic heatsink.

Performance

After wired correctly, the TDA2040 is a great amplifier. Its unlikely to be hi-fi but will compete against these far from hi-fi midi and mini systems you often see sold at car-boot sales (well in the UK anyway).

I use three of these amps in my surround sound system. This is 20W to rear left, 20W to rear right and 20W to centre. The TDA1514 operates the front channels. The sound from this system is very good indeed, more capable with movies then music, but still gives an enjoyable experience.

This amp will also suit many other purposes, I will leave you to use your imagination, but I do recommend it for its simplicity, cost and performance. Only the TDA2050 (see below) offers more power, but I have not built it yet (and it's quite expensive).

Power Supply

A power supply for this amp is simple. You need to wire up a 12-0-12 transformer in order to get +/-17V recommended. This means mains wiring so:

MAINS VOLTAGE IS VERY DANGEROUS. DO NOT WIRE IT UNLESS YOU ARE SUITABLE QUALIFIED, DEATH OR SERIOUS INJURY MAY RESULT.

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For one amp, 40VA transformer should be sufficient, meaning if you have two amps, 80VA is the recommended minimum. Capacitors should be 4700uF or bigger, rated at 35V. Feel free to increase the capacitance but you may not get much additional benefit for the price involved. A fuse should be installed, I will leave it to you to work out what's appropriate because of the world-wide mains variations. Also be sure to correctly earth the supply and any metal casing around it.

Bridge Version

The datasheet also contains the circuit for a bridged version. This has an output of 30W and uses two of the TDA2040 chips to drive an 8 ohm load. I have not yet tested a bridge version yet, but if you got a need for it then build it because its sure to give you what you'd expect. The cost will be higher, but it will still be cheap for a 30W amp. When wiring the loudspeaker, never short it to ground.

The power supply for the bridge version is the same as above, but double the transformer VA rating. This means 80VA for mono, 160VA for stereo.

TDA2050 application

The TDA2050 (datasheet here) will drop right in to the same circuit board for the TDA2040 and will operate just by changing two components:

  • R4 should be changed from 4.7 ohms to 2.2 ohms.
  • C7 should be changed from 0.1uF (100nF) to 0.47uF (470nF).

The same basic notes apply so read all the above, except that:

The Heatsink should be larger, as the TDA2050 is more powerful, its bound to have a higher operating temperature.

Supply voltage may be increased beyond the maximum +/- 20V of the TDA2040 to a maximum of +/- 25V. This can be obtained by a 15V transformer (15-0-15) and uses the same PSU circuit. As the power is higher too, I would recommend a minimum of 50VA for one TDA2050 amp, double this for two. 100VA is unlikely to be available so go for 120VA. There is no bridge version so don't even consider it. If you do wish to experiment, then you could use the simple bridging adapter in the Audio Pages. If this is used, make sure you have something like a 300VA transformer, notice that this amp will now be expensive so maybe Project 3A in the Audio Pages will give better results (and may be cheaper).

I must mention that I have not built a TDA2050 amplifier yet, but it is bound to work so long as you design the circuit well and take note of the precautions issued. If you do make the TDA2050, you can expect around 32W into 8 ohm loads.