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.
Step 2: Shaping the Amplifier Board.
It is good practice to take a picture of the board by a digital camera in macro modus, to plot it, if possible on A3 sheet, and to try to understand the structure of the board. You can see that also some additional electric components are placed on the board - switches, LED's for read/write operations.. etc. You have to decide what should be used - do you need light indication of the supply presence, do you need the volume control..
Normally, for the low noise reasons, the audio amplifier occupies a compact area, which must be identified. In this case it is about 1/3 of the whole PCB area placed at the end of the board where the chip is mounted.
The next action is to mark the part of the board which should be used, in the way that the signal paths and supply for the audio amp tracks should be kept safe. There are always some tracks which connect switches, sensors, LED's placed on the other part of the board and can be cut without any influence on the audio amp performance. For the marking I used a dark marker. Now the board can be cut. For that purpose I use usual scissors. You have to cut the board carefully some distance away from the marker line - because of the cracks, which appear during the cut. After cutting the board, it must be shaped - all sharp edges have to be polished. For that purpose an abrasive paper can be used.
Step 3: The Research Work
The task is now to connect the amplifier in the correct way.
I removed the flat cable. I plotted the picture of the PCB with the metal tracks view on a A3 sheet - to be easy to follow each track and connection. You can use markers with different color for each signal.
Let's start with the ground pin - normally the ground is the "fattest" wire on the PCB. It is chip pin #4.Using Ohmmeter you can check this. A suitable place where the ground cable ( "-" of the battery) shall be soldered must be found. There the green lack must removed from the PCB. I scratch it using a big needle. A hole for the ground cable must be drilled there.
Step 4: Power Supply Connection
After that we can mount the regulator, solder it and to bridge the ground line.
Step 5: Connecting the Mute Signal.
I connected it directly to supply line.
Step 6: Connecting the LED As Power Indicator
- the resistor limiting the current through the LED must be connected to the supply line
- the cathode of the LED must be connected to the ground line
Step 7: Connecting the Inputs
Step 8: The Joy...
I used a plastic box suitable for small radio, where a special place for the 9V ( 6LR61type) battery was reserved. I added an ON/OFF micro switch at the cable from the battery "+". I cut a holes on the box side wall for the volume control, for the audio jack, for the LED and for the micro switch knob using a dremel like tool. Finally I fixed the board using 3 small screws.
I connected the battery, switched the amplifier on.....
The sound was quite good...
Enjoy, you too!