Allan Espinosa

Audio amplifier goodness

2007 July 22

For the third and fourth activity in my TCOM 121.2 Telecommunications laboratory class, I asked the students to prepare a 200 gain (46 dB) audio amplifier using the LM386 with a bandwidth of 20-20kHz.

I required the students to perform simulations by creating a SPICE netlist. The learning curve required is very steep to meet a 1-2 week deadline for performing the activity. I pointed them to the sci.electronics.cad Usenet newsgroup to search from the SPICE .subckt model since the IC cannot be found by default in the library components of MultiSim or Electronics Workbench. There were sample demonstrations on how to generate the netlist and use the model file using LTSpice in the laboratory. My classes’ were very resourceful. To accomodate the steep learning curve, they were able to find an LTSpice symbol associated with the LM386 subckt model and was able to generate simulations using the conventional schematic capture method.

They implemented their audio amplifier circuits on a standard issued prototyping breadboard. Some were able to get gains of up to 190+ but others are still struggling to exceed a 3dB gain (hence the lab extension). After reaching the 43-46 dB gain milestone, they celebrated their accomplishment by playing with the circuit. Most of the students plugged the output of the amplifier to a speaker. Thus sounds were produced based on the frequency input in the function generator. One of my students, Dale Dy played a rendition of “Happy Birthday” using various frequencies from our signal generator and his groups’ LM386 Audio Amplifier:


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