Category Archives: Sound

Extracting audio from a YouTube video using avconv

You can download YouTube videos with the NetVideoHunter Firefox add-on. After installing the add-on, you can download a YouTube video by clicking the icon.


By default the add-on downloads the best available quality from YouTube, that is very convenient.

The downloaded file has an mp4 extension.  Using the libav command line tool avconv, you can extract the audio without transcoding. This way the process is very fast and the audio quality remains the same:

avconv -i testvideo.mp4 -codec copy -vn testaudio.m4a

The -codec copy option makes sure the audio is extracted without conversion an the -vn option excludes the video being written to the output file.

To install avconv on Debian:

sudo apt-get install libav-tools

20 Watt Class A Power Amplifier

In the nineties I built a class A power amplifier based on an article in the November 1985 edition of the Dutch electronics magazine Radio Bulletin. In 2000 I reproduced the article on my web site and added photos and extra schematics for a stabilized power supply for the preamp stage. Although some of the components are probably not available and the original website is long gone (archived on the WayBackMachine), I found it useful to repost the Dutch article: Klasse A-versterker van 20 Watt