This is a homemade amplifier that's powered by a 9 volt battery,
has an on-off switch and an audio tapered volume knob (potentiometer)
for more natural volume control.
It makes use of the LM386 amplifier chip, though I used the equivalent
Some of the things I've used it for include
and much more.
As you can see
below, I package it up in a jar usually painted black and with the
speaker in the jar's cover, though in the laser communicator I built it
into the laser communicator itself and use it for amplifying the signal
going to the laser.
the video below to hear it in
Thanks to duncanbayne on
hackaday.com for the delicious suggestion.
For the hungry crystal radio user, Jujubes!
The following is the circuit I used. I first got it from the
book "Radio Receiver Projects You Can Build" by Homer L. Davidson
and then found the same general circuit diagram in
describing the LM386 chip on Texas Instruments' website.
Crystal radio amplifier circuit using LM386 amplifier chip.
I first made and tested the circuit on a breadboard and then
moved the components over one-by-one to a perfboard, soldering
them together on the back. The layout I used is given in the diagram
below in case you want to do this too.
Testing on a temporary breadboard first.
Soldered permanently onto a perfboard.
And below is how I laid it out on the perfboard. See the circuit
diagram above for how the parts should be soldered together on
the back. The layout I used when I put it on the breadboard is given
further down below.
My layout on the perfboard.
The 9 volt battery was attached to the perboard using two tie straps.
They were put on loosely enough to make it easy to slide the battery
in and out for replacement while being tight enough to hold it in place.
Drilling 4 slots for tie straps.
Tie strapping the battery in place.
The soldering on the back.
The amplifier in the jar before painting.
If you prefer to make it on a breadboard then here's the layout I
used when prototyping.
The amplifier circuit on a breadboard.
Below is a video I made that not only demonstrates this amplifier in
action but also goes through step-by-step how to make it.