This is a ~700 mW Audio Amplifier I built based on the LM386N Chip. The reason I built it was because I had a Wireless Microphone whose Line out was only 0.2 Vp-p and I had to turn the 500 Watt Amplifier/Mixer I have up to 100% and it still wasn't very loud. This amplifier boosts the voltage 20x using the default gain of the LM386N to about 4 Vp-p. This allowed me to turn down the volume on the bigger amplifier or really pump out sound. It's also capable of powering a small speaker if you want it too. For my initial schematic I forgot to put a Filter Capacitor on the Vin and the SMPS I was using with it made crazy noise so I put a 470 uF on the board after testing it.
The schematics and gerber files are on my svn at:
I also uploaded this board to OSH Park even though I etched it myself because I needed it the next day:
Here is the board after etching. The thinnest traces are 10 mils and I made some of them 30 mils. Used my standard board making method since this is a simple design and I needed it done quick.
Here it is with the TRS jacks, LM386Ns, and surface mount resistors and capacitors soldered on. The only parts missing are the potentiometers and the Power Supply Filter capacitor that I forgot to put on the initial design.
And the top side...
Here is the finished version opened up. Panel mount potentiometers and barrel jack from radio shack. Three Capacitors from Radial Capacitor kit. Two 1/4 Inch Right Angle Headphone Jacks from Spark fun. I also got the gold pins for the power input from Sparkfun. The aluminum project box was from Sparkfun too. It's excellent, easy to drill and very sturdy. I put two strips of electrical tape on the bottom to insulate bottom of board from the circuit board. If I was concerned about head from the amplifiers I could have put a piece of thermal tape on there instead so I could get good heat transfer to the case.
Here it is being tested attached to a small speaker. Sound quality was nice. No distortion or noise after adding the PS Filter capacitor.
Here it is outdoors hooked up to the 500 Watt amplifier boosting the Microphone output. I could hear it from about 500 ft away. Its running off the SMPS 12+ Volts.