Little Gem Amplifier

the completed amplifier

I needed to build an inexpensive amp to go with the Cigar Box Guitar I built for my girls for Christmas in 2010.  Once again the inspiration for this project came from Make magazine's $5 cracker box amp.  That project was based on the 1/2W Little Gem amp from RunOffGrove.  It is a great sounding little amp with separate volume and gain controls.  It is also inexpensive and easy to build.

There was no way a cardboard amplifier was going to survive in a house with a 2 and a 6 year old.  So I dug through my pile of reclaimed junk in the basement and found a wooden index card box.  (It's so satisfying to finally use something that you've been holding onto for years for no reason other than you know you are going to need it one day!)  I purchased the electronics parts that I needed from Radio Shack.  The handle, knobs, feet, and power cord were all from an old PA amplifier I rescued from the trash.  The speaker and grill were from an old Archer speaker I found in the same trash pile.  The aluminum panel for mounting the controls came from my old clipboard that I accidentally ran over.

Little Gem schematic

visual diagram of Little Gem found here

I built the amp just as laid out in the schematics with a few changes.  I swapped the battery for a 12v wall wart that I had saved from some discarded electronic device.  I housed the transformer inside the amp to make it easier to transport.  I also added a power switch and led power light.  I used this great Dremel circle cutter to cut out the speaker opening.  The controls were recessed in the side to protect them.  The LM386 power amplifier chip was mounted in an IC socket so I could easily swap it out just in case I blew it up during construction.  The final price was probably closer to $15 rather than the $5 claimed in the original article, still cheap enough.  The hardest part of this project was finding the free speaker.  The construction itself was pretty easy.  Check my video to hear the amp in action.

inside view

the finished circuit

control mount

transformer