Tuesday, 10 February 2009

Fixing ALSA Driver

Since buying my Dell Studio laptop back in December, I had not got around to fixing the Advanced Linux Sound Architecture (ALSA) bug. The bug manifested itself in a variety of guises, as the bug report lists, but for me it meant that:

  • The front, built-in speakers were always on

  • The headphone jacks (there are two) were mute unless phones were inserted at boot-time

  • Unplugging the headphones immediately caused them to stop working

This was really annoying, but then so are exams, so I neglected to fix it.

Today however, I grabbed the latest snapshot of the driver source from: http://www.alsa-project.org/snapshot/ and compiled it from source, installed it, rebooted. Now full functionality is restored, the headphones work fully and the front speakers can be controlled independently of the master volume.

Whilst this may not seem particularly impressive, this is the first time I've ever successfully compiled from source and installed any part of the linux kernel.

I hope the fixed ALSA driver gets included into the next kernel release very soon.

Sunday, 1 February 2009

Guitar Effects Mods

I don't play the guitar, but my flatmate does. He has a collection of electric guitar effects peddles and has recently expressed an interest in modifying one of his less favoured peddles to improve the sound. This interest was further motivated by an ebook which he received at Christmas detailing common mods made to a number of popular effects peddles.

So yesterday afternoon was spent taking apart the peddle apart, making some simple changes to it and then seeing if it made a difference. After reading the instructions for the mod, I was a little sceptical as to the difference it would make to the sound. The changes involved replacing one of the capacitors with a beefier one and replacing two diodes with three diodes (one was replaced with two in series). In addition, and at the insistence of my flatmate, the LED colour was changed, so that it was obvious that the peddle had been modified.

After a couple of hours wrestling with a horribly constructed PCB, we were finished. The unit worked first time, however neither of us were sure if our changes had made a significant difference to the sound. The aim was to make the distortion effect more 'responsive' and 'thicker'. Whilst my flatmate was certain there was a difference, I am less convinced. Despite this, I learned a few interesting things about this area of electronics:

Guitar effects peddles are remarkably easy to modify. There appears to be a lot of information including schematics and suggested modifications to be found on the internet.

Some effects peddles are custom made for bands and cost a phenomenal amount.

The design of such peddles seems to be a black art. The results are very subjective and I have no idea how one would go about designing to specification such a device. If I played the guitar then I would be tempted to build from scratch a simple effects peddle which allowed you to tweak component values quickly - as I suspect this is how most peddles are designed. Although this is entirely un-researched!