USE IT.
THE ORIGINS OF THE
CRACKER BOX AMP
Blind Lightnin' Pete's cracker box amp.
A FEW WORDS FROM
BLIND LIGHTNIN’ PETE
The cracker box amp I built cost $5. It uses an 8-pin
National Semiconductor LM386 series low-voltage
op-amp IC. The amp circuit unleashes the full
potential of this beast and creates ¼ watt of arena-shaking power. Think of it as sort of a silicon shrunken
head of the Marshall stack that Jimi Hendrix played
at Monterey.
This integrated circuit has provided the basis for
low-power solid-state amplifiers in recent years,
including the famous Smokey Amp and a few of the
designs at runoffgroove.com.
Photography by Blind Lightnin' Pete
You can buy an LM386 for under a buck; it’s a
standard RadioShack item, the same one that was
used in the MAKE project for turning your old computer mouse into a robot (see MAKE, Volume 02,
page 96, “Mousey the Junkbot”). Our favorite hobbyist robot supply source, Solarbotics (solarbotics.
com), sells them for 75¢ a piece.
I added a couple of capacitors, a couple of resistors,
an LED, a ¼" jack, a potentiometer, and a $2 speaker, wrapped it all in a big blob of solder, crammed it
in whatever empty box was laying around, and voilà!
The pot controls the gain, and it goes from
California clean vintage Fender to Santana Mesa
Boogie crunch to Hendrix Marshall. It runs off any
combination of batteries — I usually use a 9V, but
it’s possible to get a cleaner tone with 12V ( 8 AA
batteries in series). I have used it to drive a 4× 12
Marshall cabinet, and it gets pretty loud. Not loud
enough to compete with a rock drummer, but loud
enough for me not to hear my wife screaming “turn
it down,” which I guess is enough for household
use. If we had any neighbors, I could raise some
complaints from it. Let’s just say that even with a 2"
speaker it’s plenty loud enough for most apartment
dwellers.
Interested in learning a bit more about the LM386?
A great place to start is National Semiconductor’s
website ( national.com) where you can download
the data sheet. Even better, if you take the time to
register on the site, they will generously send you
a few samples for free!
Ask for the LM386N- 4 series, as these are rated
to handle up to 18V. Although any of the LM386
chips will work wonderfully for our hi-gain design,
several experimenters and makers have found that
cleaner tones with more headroom are achievable
by running the circuit with a few extra volts.
OTHER OP-AMP 386
PROJECTS
Home-built bat detector:
bertrik.sikken.nl/bat/my_div.htm
Mini bench amp to test audio circuits:
makezine.com/go/minibench
Headphone amplifier:
radiowrench.com/sonic/so02144.html
See videos of Blind Lightnin’ Pete playing his
cigar box guitar through his cracker box amp at
makezine.com/09/crackerboxamp.
Make: 111
