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13 Apr 2014

In the first of a series of videos tutorials on microphones, Doug Ford, former head designer at Rode Microphones explains the basics of how microphones work, the different types – carbon, dynamic, ribbon, condensor/electret, and how the omnidirectional pattern works. Also, the internal construction of a high end measurement microphone.

EEVblog #602 – Introduction to Microphones - [Link]

9 Apr 2014


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]

28 Mar 2014


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]

25 Mar 2014



This DIY 300B triode amplifier project was completed by Stamou Tasos who is from Greece. Giovanni Militano and  Stamou Tasos write:

As a thank you for the 300B amplifier schematics, Stamou has shared with us his implementation of the 300B single-ended (SE) tube amplifier schematic by J.C. Morrison. I have assisted by translating, formating and presenting his DIY 300B triode amplifier project.

The circuit that I decided to follow for my 300B triode amplifier I found on this site, the 300B Single-Ended (SE) tube amplifier schematic with direct coupled 6SN7 input stage. Please take a look at the SE 300B schematic for a description of Mr. J.C. Morrison’s SE 300B tube amplifier circuit which I will refer to as the “original schematic”. Specifically recommended in the circuit notes was that premium output transformers and components be used for the 300B amplifier build. For this SE 300B triode tube amplifier build I have used premium parts throughout, Lundahl audio output transformers and a DIY chassis. This 300B Single-Ended-Triode (SET) amplifier circuit uses a direct coupled 6SN7 driver stage. The output stage is a SE 300B triode and the maximum power output is about 8 Watts per channel. A pair of reasonably sensitive (~91 dB+) loudspeakers will be required with this 300B SET amplifier.

DIY 300B Single-Ended-Triode (SET) Hi-Fi Amplifier - [Link]

22 Dec 2013


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]

16 Dec 2013


The basis for this tube preamplifier started out as a post in the Super simple single stage tube preamp thread on the website Forum. One of the members (see Mark’s 4S Universal Valve Preamps) had suggested building a Super Simple Single Stage Preamp (“4S” Preamp for short) and there was much discussion concerning various tubes, gain, noise, etc. and several designs were presented using various dual triode tubes. Then the proverbial gauntlet was thrown down with the phrase “switch from 12AU7 to 12AX7″. My answer was to design a universal line stage preamplifier that would work well with an entire range of tubes. Thus was the 4S Universal tube preamplifier born.

4S Universal Preamplifier for 12A*7 Tubes - [Link]

16 Dec 2013


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]

2 Dec 2013


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]

7 Nov 2013


Raffael @ code-bude.net build a webradio by himself. It’s made from an Arduino, an hacked TP-Link WR703N router and some interface parts.

Today I want to present you one of my larger craft projects. This time it is not just about software, but also about the associated hardware. What is it? A web radio!

I like to listen to internet radio stations, but I didn’t want to run my pc only for listening to webradios. Connecting my phone to my stereo either wasn’t a solution, since I’d rather wear this with me, because I don’t want to run for each SMS / Whatsapp message to the music system. And because I always like to tinker, it was obvious to build a web radio as a standalone device myself.

RadioduinoWRT – a do it yourself webradio - [Link]

19 Sep 2013


Gio Militano writes:

Until recenty my desktop computer has always shared a room with a Hi-Fi setup so there has never been a need for using decent speakers with the computer. When the desktop computer was moved into it’s own room (with no HiFi) I quickly realized that good speakers were now required for decent quality music playback. I had been using some low cost Radio Shack speakers with an inexpensive Tripath based amplifier and I was really itching for an upgrade.

Fostex FE103En Bass Reflex Bookshelf Speakers - [Link]





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