The Simplest Stereo Amplifier in the World!
If you like playing around with audio amplifier chips you'll no doubt have come across the popular TDA7052. It's an 8 pin DIL device that produces about 1 watt of audio when powered from a 6V supply. The TDA7053 is a 16 pin stereo version which was chosen for this project. These ICs use the bridge tied load (BTL) principle to drive the loudspeaker. Put simply, they work by using two power amps working out of phase with each other so that when one output goes high (up to + supply) the other output goes low (down to 0V). If a loudspeaker is connected between the outputs, then potentially nearly all of the power supply voltage can be applied across it instead of only half which is the case for a normal split rail push pull amplifier. Because output power quadruples when supply voltage is doubled, these IC's can produce a healthy 1 watt when running from only 6 volts
The circuit used is straight from the TDA7053 datasheet which states that it will work on a supply voltage of up to 18 volts. Although this may be the case, even at 12V the IC gets too hot to touch and I would not be happy running it at this temperature for very long. The optimum operating voltage is 6V and this is what I would recommend, although it also works OK on 5V which means it could easily be powered from a standard computer USB socket. A veroboard layout is shown below. Note that bridge tied amplifiers do not require output coupling capacitors which reduces the already small component count even further
If a power amplifier has no input attenuation then it's effectively always working at full volume, relying on the gain control of the source to control the output level. This is fine if used with an iPod or other headphone device as these generally have low noise figures, but when used with a PC and its grotty onboard sound chip, computer generated noise can be a problem. Even with the volume set to zero, some computers still produce lots of electrical noise which will be passed on to any externally connected amplifier. If the amplifier does not have a volume control it will be working at max all the time and any noise at the input will be clearly heard. This can be minimised by adding a potentiometer between the computer and amplfier to reduce the level, and then adjusting the overall volume using the PCs volume control. This is what I've done here, but rather than using a panel mounted pot, I opted for preset pots instead, because once set, they should not need adjusting again (and also because they are more convenient to fit!). There are other versions of these ICs that feature built in DC volume controls (The TDA7052A and TDA7053A) but they also have a higher quiescent current so were not used
The enclosure and connectors are a matter of personal choice. I used a coaxial 2.1mm socket for DC power and a 3.5mm jack for audio. The loudspeakers are connected via a 4 way screwed barrier strip, though alternatively this could be push terminals or even RCA phono sockets. The enclosure does not have to be metal/screened as the inputs are not too sensitive and so do not pick up any stray hum. I used a plastic project box from eBay
To set up the levels, turn the presets to minimum (clockwise in this case) and then set the source volume to maximum. Play some music and adjust the presets anticlockwise until the sound level is just about bearable (and equal from each channel). Reduce the source volume back to a comfortable level. From now on the source volume control will have a nice adjustment range