It can be used with different devices - MP3 players, Walkmans, Radios, .etc. It can be used also for your own designs - can be connected to the analog outputs of audio DACs, to the outputs of self made radios (for example using TDA7000, or TA7642) or other gadgets.
In comparison with the other instructables, this will not give you an exact instructions how to do the job, but will give you the idea and show you for example how it can be realized in a particular case. The success of this project will relay on your imagination and capabilities ...
The main idea here is - why to make something from scratch, if it exists...
Where an existing audio amplifier can be taken from?
The answer is - from a defect computer CD-R,W, DVD-R,W reader, writer, ROM-drive..
All they have audio output for headphones, which has almost always a volume control.
When those devices broke, normally the malfunction is always in the mechanics, in the laser system, in the optics, but, I think never in the audio headphone amplifier.
Where to find a defect drive?
You decide - at scrapyard, at the place were you company throws away the broken equipment for recycling, in some garage sale, to ask your friends, eBay...
Let's suppose, we have found our defected drive.
Let's go for the first step.
Step 1: Exctracting the audio amplifier board
The audio amplifier board is normally placed directly behind the front panel of the drive. The PCB in most cases has a long narrow shape. Between the audio amplifier board and the "main" board of the drive a flat cable connection is done. Unsolder it from the main board. May be will be possible to use it, if needed.
Do not forget to extract also the laser diodes and the electric motors - they can be used for other instructables.
On the pictures can be seen the extracted board, which was placed behind the front panel and contains the audio amplifier.