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Building A Little Gem Practice Amp
Last Updated 09/12/04
By Paul J. Marossy
I built this amp just for fun. I had a
LM386 IC chip lying around that I wanted to use for something, and so I thought it might be fun to
build a 1/2 watt solid state amp that you could take pretty much anywhere, like you can with a
Pignose amp. The circuit used is called the "Little Gem", and it can be found at www.runoffgroove.com.
The circuit is extremely simple to build, and it can be made with parts that are available at
RadioShack. I built this per the schematic except for substituting the 220uF output cap with a
330uF one for more bass. Below is some pictures of this project.
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The first thing that had to be done was
to create a chassis. This is simply a 5"x7" piece of galvanized sheet metal which I
purchased from the roofing section at Lowe's for less than a dollar. It is just
bent at a 90 degree angle. This will be attached to the cabinet and will give the
appearance of a real chassis.
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Here, the chassis is mounted to the cabinet using six screws. Before the chassis
is attached to the cabinet, it feels rather flimsy, but after it is attached, it
actually feels pretty solid.
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This is a close up of the actual circuit, built on perfboard and mounted on 1" high
standoffs. The circuit is quite simple - only an IC chip, four caps,
one resistor, a 5K pot and a 25 ohm rheostat. It doesn't get much simpler than that...
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Here is a top view of the installed chassis. From left to right: input jack, gain control,
master volume, DC power jack and on/off switch. I used a different kind of material to cover this
cabinet - a desert camoflauge material that I had left over from a project a few years ago.
I think it looks kinda cool.
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Here are the speakers that I used, a pair of 50 watt 4" 16 ohm speakers wired in parallel, mounted to
3/8" thick speaker baffle. The speakers and baffle were picked up at a local thrift store for
four dollars. I removed them from the original speaker cabinet and used the back of the speaker
cabinet for my new speaker baffle, which is a particle board type of material.
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Here is the finished product. I pretty much did this project with parts I had lying around. The
cabinet is made from 1/2" particle board. The overall dimensions of the cabinet are:
10.5 inches wide, 8 inches high and 6.75 inches deep. Weight is approximately 8 to 9 lbs.
Even though the speakers are small in size, it sounds like a much bigger amp than it is.
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