Bruno Putzeys writes:
I hate articles titled “Ten … myths debunked.” I would have to start by listing a round number of clumsily worded claims by the non-feedback camp who probably never said any such thing, and juxtapose some simplified school-book explanations to put them right. And after shooting, flaying and roasting alive my straw men and generally hammering home that feedback doesn’t work like that, I should then fail to explain why not. This would leave an excellent status quo where everyone has had their say and truths remain somewhere in the middle.
Negative feedback in audio amplifiers: Why there is no such thing as too much - [Link]
The cMoy is a headphone amplifier kit based around a single dual-channel opamp, suitable for use with portable audio equipment, smartphones, computers etc. It is based on a design well-known in the DIY Audio community. Akafugu writes:
We’ve partnered up with Praktisk Audio, a newly launched audio brand and made it into an open source hardware kit that is easy to assemble for anyone looking for a starting point into the world of DIY audio.We use high-quality parts sourced in Japan, including Rubycon capacitors and a NJM4556AD opamp. The potentiometer is a 10kΩ ALPS potentiometer with built-in on/off switch.The cMoy comes as a kit, and includes the PCB board and all the components you need.No amplifier would be complete without an enclosure, so we are offering a choice of two beautiful aluminum enclosures. Both are Made in Japan by the company Takachi.The standard enclosure is in aluminum with custom-made black acrylic front panels. The deluxe enclosure comes with beautiful custom-cut aluminum front and back panels with high-quality silk screen.
Cmoy Headphone Amplifier Kit - [Link]
Potentially, headphone listening can be technically superior since room reflections are eliminated and the intimate contact between transducer and ear mean that only tiny amounts of power are required. The small power requirement means that transducers can be operated at a small fraction of their full excursion capabilities thus reducing THD and other non-linear distortions. This design of a dedicated headphones amplifier is potentially controversial in that it has only unity voltage gain and employs vacuum tubes and transistors in the same design.
Hybrid Headphone Amplifier – [Link]
Boris Landoni @ open-electronics.org writes:
Today we present you a stereo 10 + 10 Watts audio amplifier based on TDA7297SA, a monolithic dual bridge amplifier that is suitable to be used in projects that feature access to a single 12 volts power supply.This is a compact stereo amplifier: its field of application range from car stereo to portable audiovisual equipments (eg: for sport or public events, conferences or even emergency protection and safety mission equipements such as those needed after distaster events)The heart of the amplifier is the TDA7297SA integrated from STMicroelectronics, a monolithic dual bridge amplifier capable of delivering, in fact, 10 + 10 watts.
A versatile, powerful 10 + 10 W Audio amplifier - [Link]
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]