Here is a design guide from Maxim describing various classes of audio amplifiers. [via]
This has been a brief survey of the many types of audio amplifiers commonly used in designs today. Clearly, when designing an audio circuit for any type of device, care should be taken in determining the audio amplifier topology best suited to the application. A good understanding of these different classes of audio amps will help you choose the best audio amp for your design.
App note: Various audio amplifier classes - [Link]
Here is a simple and reliable 2.5W Stereo Audio Amplifier based on TEA2025 IC. Nydal Dahl writes:
I have been looking for a good stereo amplifier circuit diagram for a long time. I am not a HiFi geek, I just wanted to build a simple stereo amplifier that could drive some speakers for my desktop computer.All the schematic diagrams that I could find seemed to involve lots of hard-to-find components or you had to use it together with a pre-amplifier or some other amplifier stage. It was always something that made me hesitate.
TEA2025 – 2.5W Audio Stereo Amplifier - [Link]
The LM4780 is a great part to build your own Audio Power Amplifier. It is not a new part, but is a very popular part used audio amplifier circuits. This part is spec’d to drive two 8Ω loads at 60 watts. The part comes in a wide TO-220 package and can be mounted to a heat sink. Pay attention to the voltage on the thermal tab it is a voltage supply not gnd.
This circuit demonstrates how easy it is to configure the amplifiers.
Build your own Audio Amplifier Circuit - [Link]
Gio @ diyaudioprojects.com point us to:
This is a project that has roots to back about 2 years ago. I wanted a quality headphone amplifier to be an addition to my Hi-Fi stereo system. It was to be something to use when I didn’t want to disturb everyone else in the house. I tried several different tube types in the amplifier design process. I used 6J6, 12AU7, 6SN7, 6CG7/6FQ7 and 12AT7. Generally all worked, but none seemed to have either the needed output level or didn’t match well (likely to the choice of transformers) and sounded on the dull side. The 6DJ8 (ECC88) dual triodes worked like a charm. They had the combination of sufficient current flow, modest voltages on the anodes (important for the matching transformers) and enough gain to make the amplifier sing. The next best tube type was the 6CG7/6FQ7. Almost as good, but they are getting a bit scarce and the new production JJ E88CC are now quite common and reasonably priced. I am sure other triodes could be used and there is no reason why a high impedance ( on the primary side) small push-pull output transformer would not work. I doubt that you can find one much cheaper than the matching transformers I used. Certainly not with similar response and distortion characteristics.
DIY 6DJ8 (ECC88) Tube Headphone Amplifier - [Link]
Bruce Heran writes:
It has been a while since I did anything really crazy in DIY and had it work out far above my expectations. Such is the case for the Mini Blocks. I had a lot of extra parts lying around (really a huge amount of them) and tried to figure out what I could build. Two small chassis about 5 inches by 9 inches by 2 inches (12.5 X 22.5 X 5 cm) were just begging for a project. They are just the right size for lots of things. I first thought of a pair of SET amps. But since I didn’t have any suitable single ended output transformers I nixed that idea. A preamp perhaps could be built on one of the chassis. Since I have many preamps now that didn’t really get the nod either. A pair of small push-pull amplifiers was next on the list. Maybe, but I have so many amps now that it doesn’t make sense either. Since this hobby doesn’t always have to make sense, that is what I built. Clever observers will note that each of the mini blocks is a whole lot like half of a PoddWatt amplifier
Mini Block Push-Pull EL84 (6BQ5) Valve Amplifiers - [Link]
The TDA2003 has a better performance than the TDA2002 using the same pin configuration. Additional features compared to TAD2002, requires few external components, easy assembly, is a low cost solution to an audio amplifier. A mounted amplifier with TDA2003 features protection against short pins to ground.
TDA2003 Power Amplifier - [Link]
Amplifier with TDA7294 of the ST microelectronics, you can get power up to 100W in a single chip.
TDA7294 Power Audio Amplifier 80W - [Link]
This circuit is a complete 2.1 amplifier for two satellite speakers and one subwoofer.
TDA2030 Audio Amplifier with 2.1 – 3 x 18 Watt – Subwoofer - [Link]
This is a PDF in English published in 1947 and features 45 complete schemes of tube amps, including diagram drawing material list and description of operation. Ideal for anyone interested in old amplifiers (Vintage) and the supporters as well as a modern valve amplifier. The power of the circuits presented in the book ranges from 1 to 75 Watts.
Practical Amplifier Diagrams – Tubes Audio Power Amplifiers - [Link]