In this episode Shahriar presents a tutorial on the design and characterization of a single-stage low-noise bipolar amplifier suitable for audio applications. Given a set of specifications, a common-emitter topology is investigated. The circuit employs a beta-insensitive biasing scheme which is simultaneously optimized for maximum output swing. The small-signal gain of the circuit is calculated and the bandwidth is set for audio frequencies. A non-inverting operational amplifier is used as a second stage to achieve the desired overall gain. The circuit is assembled on a breadboard where the gain and bandwidth are measured and compared with design specifications. As the final experiment, the circuit is used to amplify signals from a microphone.
Tutorial on the Theory, Design and Characterization of a Single Transistor Bipolar Amplifier - [Link]
Acidbourbon posted a step by step guide of his digitally controlled HIFI amp with 4 way mixer build:
The amplifier section is trivial. You just buy a TDA1554Q, bolt it to the inside of an aluminum box, solder some resistors and capacities to the pins of the IC according to the application note in the datasheet and you have a small HiFi amplifier.
Because the volume control has to be digital, I’m using digital potentiometers. Sadly there are no (affordable) logarithmic digipots available. However I found this method which employs a linear potentiometer in combination with a fixed resistor to “fake” a logarithmic potentiometer.
Digitally controlled HIFI amp with 4 way mixer - [Link]
This 1w audio amplifier circuit is designed using NCP2830 audio IC manufactured by ON Semiconductor. This audio power amplifier ic designed for portable communication device applications and require few external electronic components. NCP2830 is capable to provide 1W continuous output power in 8 ohms load. NCP2830 audio power amplifier main features are : high quality audio (THD+N = 0.04%) , low noise: SNR up to 100 dB, overall system efficiency optimization: up to 89% , Superior PSRR (−88 dB): Direct Connection to Battery , Very Low Quiescent Current 7 mA , Optimized PWM Output Stage: Filterless Capability , Selectable gain of 2 V/V or 4 V/V .
1W audio amplifier circuit using NCP2830 - [Link]
Long term reliable contact without interference, creaking and hum, moreover in a beautiful coat – these are the Neutrik / Rean connectors.
Connectors have in general one interesting feature – there are many similar or almost the same connectors on the market. Audio connectors are not exception in this. Even though they look the same, many times there are huge differences in price and mainly in quality. If we supposed, that every producer designs and makes his products likewise responsibly, then the cheaper one should be probably a good choice. Naturally, in praxis it isn´t so.
A real difference between a quality and a low-class connector can be known only at a close-detail investigation and comparison, and ideally after a real testing in praxis.
Quality audio connector must be made of quality materials and also with a high precision. Naturally, if a producer wants to achieve success on a market, it´s often simply impossible to use a too expensive connector, which would over-price the whole device.
That´s why you can find in our store the Neutrik / Rean connectors offering a high-end class for a very reasonable price. Company Neutrik specializes already for almost 40 years in audio connectors and in general connectors for audio/ video studios, equipment of concerts (backstage) and similar, that´s why also in loudspeaker connectors, power supply, Ethernet,…
In the Neutrik products can also be found connectors Rean representing even more affordable price level while maintaining a very high quality. Already a short look at details of Neutrik/ Rean connectors will tell us, that we´re dealing with precision connectors. A matter of course is a detailed documentation with an exact description of electrical features and materials used. A comprehensive overview about available types will give you the Rean catalogue and the Neutrik catalogue (22MB). To many sophisticated connectors like for example NYS373 there are also available assembly instructions.
Uncompromising quality audio connectors for a compromising price - [Link]
Eric Rosenthal and Michelle Temple have developed a low cost open source DIY hearing assistive device through hole component kit called Wear. Wear is a device that was made to provide a low-cost hearing aid alternative for individuals who suffer from hearing loss and is designed to be used when a hearing impaired individual is interested in having a quality conversation in very noisy environments like family gatherings, restaurants or meetings.
This wearable assistive device has been engineered and designed to improve the quality of conversation, while aiding in reducing extraneous noise. Similar to listening to your iPod, users connect their personal headphones to the device that is worn around the neck. The microphone creates a directional sound lobe 3-6 feet in front of the user. The device amplifies sound directly in the circular zone in front of the user, while reducing noise outside of the zone. The Wear can also be used as a high quality commentatorʼs microphone, for interviews or for general recording.
Latency (delay) imposed by digital signal processing is detrimental to the hearing impaired due to lip sync (lip reading) difficulties. For that reason we used an analog circuit design with no measurable latency. We incorporate a technology using a beam-forming array of 10 microphones that create a circular 6 foot zone. Acoustic waves generated in that zone (coherent) reach the microphones at the same time so they are amplified. Sounds from further away (non coherent) reach the microphones at different times are not amplified. This creates a near field to far field signal level difference of 10 to 11 db. That 10 db level difference improves the intelligibility of near field conversation. Our research over the past two years has allowed us to reduce the size of beam forming arrays to unprecedented small form factors in a lightweight package using low power. All of this is done without digital signal processing while maintaining hi fidelity sound quality so that the directional microphone can also be used for general recording applications as well as an assistive hearing appliance.
The open source kit uses through hole components and comes complete with double sided circuit board, all components, a battery, and assembly instructions.
Wear – A wearable personal assistive hearing device - [Link]
Make your own computer speaker system. This simple and inexpensive project will let you set up a small audio amplifier circuit and let more sound out your computer.
A simple audio amplifier circuit based on the LA4440 IC. This circuit will take your computer’s headphone level output and amplify it to drive a pair of external speakers. If you are listening to music or movies on laptops and computers, this is a useful little project for you. Laptop speakers are never loud enough to give satisfying listening. They give users the ability to hear something, but for anything like music or movie soundtracks they are very poor performers. The output from a laptops built in speakers is just too low, and this circuit addresses that low power with some additional amplification.
This circuit uses an LA4440 and some supporting components to give you much more power, while retaining a small package that you can use. The LA4440 is a dual channel audio power amplifier, with low distortion, and a good frequency range. Using 2 channels, the LA4440 will output 6 watts per channel, that can drive much larger speakers than a laptop can hold. When you set up a small enclosure(s), a 12V power supply, and an audio jack connection to the laptop you’ll have a nice enhancement to your laptop audio enjoyment.
Laptop Audio Amplifier - [Link]
Milen @ instructables.com writes:
The purpose of the project was to create an external USB audio card, which could be able to:
1) serve as usual external USB audio card with headphone/line output and audio line input
2) can transmit the digital audio data at relatively long distance (20m -100m)
3) can receive and process the digital audio data send by the similar card and either transfer it through the USB to the PC, or convert it to analog audio signal
As long distance transfer media was chosen the POF.
A short explanation of the POF technology will be presented:
External USB audio card with optical S/PDIF POF interface - [Link]
Occupying a footprint of just 2.57×3.24 mm, the STA333IS single-chip digital audio system from STMicroelectronics furnishes up to 20 W of audio output power for use in space-constrained LCD and LED televisions, docking stations, and digital wireless speaker systems. With is wide operating voltage range of 4.5 V to 18 V, the device is also suitable for battery-operated equipment.
Part of ST’s SoundTerminal family, the STA333IS combines digital audio IP, such as FFX full flexible amplification, along with signal processing and power circuitry in a chip-scale package to create a high-power, single-chip solution for all-digital amplification. Its power section consists of four independent half-bridge stages. Two channels can be provided by two full bridges capable of delivering up to 10 W + 10 W of power.
Tiny digital audio SoC delivers up to 20 W - [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]
O’K, after having some fun with stereo version of the VU meter I described in my previous blog-post, now it’s time to do a serious stuff. Studio grade VU meter !!! 24 steps, equally spaced every 3 dB, covering Extra wide Dynamic Range from -63 up to +6 dB. Single (mono) channel this time, no messing around, absolute precision at the stake. Plus, it keeps absolutely Top-Flat linear frequency response from 40 Hz up to 20 kHz(*).
Audio VU meter with extra wide Dynamic Range 69 dB - [Link]