I wanted a simple audio amp to play my iPod thru speakers when I am working on electronics. So I chose the LM386 Audio Amp to build a simple stereo. Initially, I checked the voltage output from the iPod headphone jack and compared it to the output from my computer. I used a 2 channel digital oscilloscope to look at the average and peak voltages from different songs. I noticed that the voltage output of the iPod was just a little more than half the output voltage compared to the computer, or about 100-300mV. The base 386 is configured as a 20x gain amp, which would result in an output voltage in the 2-6V range. The speakers I had were 25 ohm, so the power requirements were less than the 0.5W rating of the 386. I used one 386 each for the left and right channels. There was slight hum in the speakers, so I added a 100mF capacitor from Vcc to ground to effectively short out the high frequency hum from the power supply. The sound is pretty good, though it doesn’t have much bass. Next, I want to see if the 386 chip has enough power to drive higher quality, 8 Ohm speakers.
I shared my design with an electronics design engineer that works with my Dad, and he liked the overall design. He gave me some tips about avoiding ground loops by placing the return of the speaker as close to pin 4 (ground of the amp) as possible. Also, he suggested bypassing Vcc to ground right next to the audio amp by placing a 2.2uF tantalum capacitor in parallel with a 0.1uF ceramic cap.
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