02 August, 2003

Unleashing the LM386

From Wikipedia Commons, author 'Samba pa ti'
The LM386 must be one of the most popular audio output amplifiers among radio amateurs, despite having been around for a long time. It's an IC which even has its own Wikipedia page. The LM386 can be obtained in both dual-in-line and surface-mount packages and outputs 325 mW in the standard version that runs from 4-12 Volts supply voltage.

Its voltage gain of 46 dB is in many cases too little, especially in direct conversion receivers. When I built the Pixie 2 with the LM386 audio stage, it struck me how the sensitivity of the receiver was limited by the audio gain. I asked myself if it would be possible to increase the gain and add some filtering in a simple way. The result is a gain of more than 70 dB and an audio bandwidth of a few hundred Hz by only adding 5 passive components to the standard circuit: 3 resistors, 1 capacitor and an inductor.