Medical grade hearing aids are very expensive, if a person needs help hearing but not necessarily the full cost and capability of a prescribed hearing aid, this might be an option.
This is a less expensive, and DIY option for a hearing aid. It is not a substitute for a real hearing aid that an audiologist would prescribe. Amplification of all sounds and frequencies, or constant use in loud environments can cause additional hearing loss. This circuit could be helpful for some types of hearing loss and occasional use, as well as fill in during the average amount of time people wait to get a hearing aid (7 years).
The condenser microphone picks up acoustic signals, that then pass through the preamplifier stage composed of Q1, a BC547 transistor and a few resistors and a capacitor. The output from the BC547 preamplifier is then fed into the input for the amplifier circuit through the variable resistor R1 and C2. IC1 is the amplifier, a TDA2822M which is designed for low-power portable applications, and in this case, the output is bridged to drive the single earphone. A small LED is included to indicate power status and hopefully remind you to turn it off when you take it out.
A Low Cost Hearing Aid - [Link]
By Bill Schweber:
In a wireless design, two components are the critical interfaces between the antenna and the electronic circuits, the low-noise amplifier (LNA) and the power amplifier (PA). However, that is where their commonality ends. Although both have very simple functional block diagrams and roles in principle, they have very different challenges, priorities, and performance parameters.
How so? The LNA functions in a world of unknowns. As the “front end” of the receiver channel, it must capture and amplify a very-low-power, low-voltage signal plus associated random noise which the antenna presents to it, within the bandwidth of interest. In signal theory, this is called the unknown signal/unknown noise challenge, the most difficult of all signal-processing challenges.
Understanding the Basics of Low-Noise and Power Amplifiers in Wireless Designs - [Link]
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]