Hi Gang! I've been asked a lot how to make an amplifier
for a crystal radio, one that plays loudly on a speaker.
As you can see I got a little fancy and made a permanent one in this jar.
I'll show you how I made it step-by-step, and how you can make one too.
I originally saw the circuit from this good book.
It uses an LM386 amplifier chip. When I looked up LM386 online,
the first document I found was from the chip maker's website,
Texas Instruments. And in that document I found the very same
circuit with additional details about the chip.
The book information and the website link are in the description below this video.
Here's the circuit for my crystal radio. And here's the earpiece that's used to listen
to the radio. That's the part that this amplifier replaces.
And here's the amplifier circuit it gets replaced with.
And this is how I arranged it all on my perfboard. I'll be following that step-by-step.
Here are the parts you'll need.
First the capacitors. Two 10 micrfarad electrolytic capacitors.
A 0.1 micrfarad ceramic capacitor. Two 220 microfarad electrolytic capacitors.
And a 0.047 microfarad ceramic capacitor.
For controlling the volume, you'll need a 10 kilo ohm potentiometer,
or variable resistor. The volume will be controlled by turning the
knob. Mine is audio tapered, or log tapered.
The alternative is linear tapered. The type of taper tells you how the resistance,
or volume in this case, changes as you turn the knob.
Here's a graph showing you a linear taper. You can see that when the knob is turned halfway,
the volume will be at half. But in this audio, or logarithmic graph,
when the knob is turned halfway, the volume will be around 16%.
At least that's what I got when I measured my audio potentiometer
at what looked like halfway. Audio ones exist because of the way humans
tend to expect volume to change as they turn the volume knob.
You'll also need a 10 ohm resistor.
A simple on/off switch.
A 9 volt battery, and some way of attaching to the battery.
A small speaker, usually one that's 8 ohms. This is a permanent magnet type of speaker,
which I took from a toy electric guitar.
And an LM386 amplifier chip. My local electronics store didn't have an
LM386 but they had an equivalent one called NTE823.
If you can't find an LM386, just look for an equivalent or replacement
part.
I didn't want to solder directly to the pins on the chip
so I got a socket for plugging it into. I'll solder onto the socket's pins instead.
I want this one to be permanent. So instead of doing my usual breadboarding,
I got this perfboard for soldering everything on to.
And now for how to make it.
The first thing I did was to plug it all into a breadboard,
to test it. The placement of the holes in the perfboard
match the holes in the breadboard exactly,
so it's easy to move it all permanently to the perfboard afterward.
The whole thing will be mounted inside this plastic jar.
So taking into account the breadboard and the size of the jar,
I mark the perfboard, and cut it.
The battery will be mounted on the board. So I drill out some larger holes,
and use some tie straps to hold the battery in place.
I pull them only tight enough to hold it while still allowing me to slide it out for
replacement.
I'll start with the chip. Looking closely at it you'll notice it has
eight pins, and in this corner is a round dot.
That dot means the pin at that corner is pin 1.
From there we know that this is pin 2, 3, 4, 5 and so on up to pin 8 right here.
I'll be soldering to the socket and not the chip directly,
so I put the socket in the perfboard, in a place that corresponds to where the chip
is in the breadboard. On the back I bend a few of the pins to hold
it in place.
On the breadboard, this row of holes are all electrically connected
together. I use that row for connecting to Earth ground,
and battery negative. So I make a mark on the perfboard along the
corresponding row.
Put one end of a red wire in this hole and the other end in this hole.
Make sure there's plenty of bare wire on both ends
for soldering to things. That'll connect pin 6 to battery positive
later.
Put one end of a black wire in this hole and the other end in this hole.
That connects pin 4 to ground.
While we're at it, connect a wire from this hole to this hole.
That connects pin 2 to pin 4, but remember, pin 4 is connected to ground.
So we're really just connecting pin 2 to ground.
Put one end of a red wire in this hole and another in this hole.
Later we'll be putting a few other things in these holes
to connect them together. So pin 5 will be connected to them too.
And lets do a similar thing by putting a wire in these holes.
That'll connect pin 8 to something else.
That something else is this 10 microfarad electrolytic capacitor.
Since it's an electrolytic capacitor, it has a positive leg and a negative leg.
The negative leg is indicated by this stripe or minus side here.
Put the positive leg in this hole next to the red wire we just put in.
Put the negative leg in this hole next to pin 1.
So in the last two steps we just connected pin 1 to pin 8
through this capacitor. We did it in two steps because the chip will
be in the way.
It's getting a little crowded back here so I'll solder a few things together to make
room. To save headaches later, after each solder
I check it with a magnifying glass and my meter.
The solder joint was successful so I trim the excess wire and move on.
And here's the result after this batch is done.
Put the 10 ohm resistor in these holes. That connects one end to ground.
Put the 0.047 microfarad capacitor in these holes,
oriented either way. That connects it between the 10 ohm resistor
we'd just put in, and pin 5.
And to finish off that area, get one of the 220 microfarad electrolytic
capacitors. Put the positive leg here and the negative
leg here. That connects it between pin 5 and the speaker,
which we'll put in later.
Next, put the 0.1 microfarad capacitor in these holes.
Orient it either way. That connects it between pin 7 and ground.
And lastly for that side of the chip, take the remaining 220 microfarad capacitor
and put the positive leg here and the negative leg here.
That connects it between pin 6 and ground.
Take the remaining 10 microfarad electrolytic capacitor
and put the positive leg here and the negative leg here.
That connects it between pin 3 and the middle of the potentiometer,
which we'll connect next.
The potentiometer has 3 legs to connect to. So I solder a black wire to this leg,
a yellow wire to the middle leg, and a red wire to this leg.
The wires have to be fairly long since this potentiometer will be
mounted in a hole in the side of the jar. To connect it up, I put the black wire here,
the yellow wire here and the red wire here.
That connects the black to ground, the yellow to the 10 microfarad capacitor
we'd put in during the previous step, and the red will go to the crystal radio's
output later.
I'll put a very long red wire in the hole beside the red wire we'd just put in from
the potentiometer. That will be going out a hole in the jar
for connecting to the crystal radio's diode.
Next for the speaker. I'll put the black wire here and the red wire
in this hole here. The polarity doesn't really matter.
That connects the speaker between ground and the negative leg of this 220 micrfarad
capacitor we'd put in earlier.
I've soldered some long wire to two legs of the switch
because the switch will be mounted in a hole in the jar somewhere.
I'll put one wire here and the other wire here.
That connects one end to the red wire that goes to pin 6
and the other end to the battery positive, which we'll do next.
This is the connector for plugging into a 9 volt battery.
I put the red wire, which is battery positive, into this hole and the black wire here.
That connects the positive to the switch and the negative to ground.
As you can see, I've been soldering and testing connections
as I went along. The last thing to do is solder all these ground
wires together. For that I prepare a long wire
with a long piece of insulation stripped off it.
I put it in this hole and bend the bare part to reach all the parts
that should be grounded. And here it is all soldered.
Now I can insert the chip. Remember to pay attention to the dot on the
chip that tells you where pin 1 is.
And that's it!
Now to mount my crystal radio amplifier in a jar.
First I permanently put on the tie straps for holding the battery.
Then I make holes for the potentiometer, or volume control knob,
and the on/off switch. Then I make a nice big hole in the cover for
mounting the speaker. I also cut two slits in the side
for the wires for connecting to the crytal radio.
I put everything in place. I hot glue the speaker in place.
I also attach alligator clips to the wires for connecting to the crystal radio.
I painted the jar black and made some nice labels for the volume control
and switch. I fasten the potentiometer and switch,
and screw on the cover. Done!
Time to have some fun! Here's my so called indoor crystal radio.
I first connect the red wire to the crystal radio's diode.
Then I connect the black wire to the crystal radio's ground.
As you can hear, it's fairly loud.
Now to try out the volume knob.
And here's my portable crystal radio in a pizza box!
Well thanks for watching!
See my youtube channel, rimstarorg for more videos like this.
That includes one showing step-by-step how to make
your own indoor crystal radio. And another showing how to make a portable
pizza box crystal radio. And for variety,
see how radiation works using an Americium pellet from a smoke detector
as an example.
And don't forget to subscribe if you like these videos,
or give a thumbs up or leave a question or comment below.
See you in a bit!