Simple and High Quality Audio Amplifier:

 So here is another circuit. I have posted the pictures of what i built using this circuit. Its a tiny amplifier schematic that can be used to drive the large speakers. I 've shown in the diagram the lm386 which is an opamp available in DIP and SMD. This chip is fantastic thing & very popular everywhere. It can be found in any radioshack or our local electronics stores. Most of the mp3 players coming from china now a days uses this amp. Given below is the schematic that is the basic version i designed and below this there is the modified version with explanation. 

You can click on the image to enlarge it. Well here are some important things i think i must mention here. So please read them if you are a beginner :

1. The Capacitor 47nf    = 0.047uf = 473pf
2. The Capacitor 100nf  = 104pf
3. Potentiometer must be of 10k if you bring 50 k then put a 102pf capacitor between wiper of potentiometer and ground.
4. To get some extra gain put 10uf  capacitor (of 50v) between pin 1 and 8 of IC.

Components Required:

• IC - LM 386 or C386
• Capacitor 100nf
• Capacitor 473pf
• Capacitor 330uf at 16v
• Capacitor 100uf at 35v
• Resistance 10 Ohm  [ 0.25Watt ]
• 9v Battery or a 9v DC clean power supply

I never liked the diagram people provided on the internet that is quite similar to the above one. Because it contains a huge noise and distortion signals at output. Also 47nF and resistor 10R in series between pin6 and ground which is used to prevent noisy signals found to be useless. So after a lot of experiments i came to a decision that just a single 100nF capacitor was fine to bypass those unwanted noisy signals. Below the modified version is given:

 Firstly, lets discuss the input. So, in the previous circuit we used potentiometer and here i am using two 1K resistor parallel? No, they're not parallel. They are the left and right channels for input. This is due to many persons asked me about "how to use it to listen stereo?" and so, i simply added a mixer circuit at input using 1K resistor (yes its simple and cheap method to do so, however there are also several other ways).  Now you can listen to the good to both channels of stereo audio but not like stereo effect. Shorting the left and right channel is not suitable and recommended method. Just use this method which can be called a passive audio mixer in order to mix both of the channel of incoming audio. However you won't be having a stereo output as there is just a one speaker and just one input at IC lm386 pin 3 (But you can use two amp-circuits for that). But i think that it is just fine if you're about to listen to the audio just for fun. So, in the above given schematic you can still add a stereo potentiometer if you want. A value of 10K would be fine will provide you good range of setting the input gain. 
I saw many people use a 10uF capacitor between gain pins 1 and 8 of IC386, i don't recommend that because i experimented on it resulted in blown chips and one time it caught fire on the breadboard which caused my beautiful and expensive breadboard look horrible. The amp chip was draining alot of current than expected in order to increase the gain however i didn't have a low current power supply so it got blown. Anyways;

Circuit on vero-board can be more compact as follow:

Keep the wires that you use to create connection between IC pins and other components as shortest possible. This would prevent unwanted noise from surroundings or any electric device near it. Or maybe it caught the radio frequency sometime. 

Components Lists:
LM386
8 pin DIP socket
1000uF-16v Capacitor
100nF ceremic Capacitor (Code for which is 104)
2pcs 100uF - 16v Capacitor
2pcs 1K resistors 0.25W 

To build a good amplifier never salvage capacitors. Use new one with accurate values mentioned. In order to make it sound clean forever use a metal project enclosure box and never forget to connect the amplifier circuit's ground wire to it. 
Good Luck.! And Have a wonderful project. (Y)