The $5 Cracker Box Amp

By Ed Vogel
Category: Music
Time Required: 1-2 hours
Difficulty: Moderate

In MAKE, Volume 04, I presented my version of the venerable cigar box guitar, which included an electric pickup so you could play the guitar through an amplifier.

People from around the world emailed me to tell me they’d built cigar box guitars based on my instructions. I struck up a conversation with one gentleman from Europe who goes by the moniker Blind Lightnin’ Pete. He made a couple of beautiful cigar box guitars, including one he calls the Vintage Blues Texas Rattlesnake Special model. He then went one step further, and built a cracker box guitar amplifier.

This outstanding little amp cost me all of $5 to build, since I had some parts lying around (you’ll spend more like $30 if you buy all the parts from scratch). Pete kindly allowed me to modify his design and present it as a project for you to build. (See Step 8 for a word from Pete about the origins of the cracker box amp.)

My amp differs a little from Pete’s because I wanted to make a workable little practice amp with parts and tools that could be purchased “one-stop shop” at RadioShack and built in an hour.

Steps

Step #1: Download the schematic.

Download the PDF of the schematic from the files above and print it out. NOTE: Cairn Idris designed a circuit layout diagram that is much easier to read than this schematic.

Step #8: A Few Words From Blind Lightnin’ Pete

The Origins of the Cracker Box Amp
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 1 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 http://runoffgroove.com.
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, Mousey the Junkbot). Our favorite hobbyist robot supply source, Solarbotics, sells them for 75¢ a piece.
I added a couple of capacitors, a couple of resistors, an LED, a 1/4“ 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 412 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 (http://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.
See videos of Blind Lightnin’ Pete playing his cigar box guitar through his cracker box amp at http://makezine.com/09/crackerboxamp.

Conclusion

This project first appeared in MAKE Volume 09, page 104.

Related Posts on Make: Online:

Cracker Box Amp Subwoofer

http://blog.makezine.com/archive/2009/04...

Coconut Amp

http://blog.makezine.com/archive/2008/02...

Flashback: Cracker Box Amp

http://blog.makezine.com/archive/2009/05...

5 Responses to The $5 Cracker Box Amp

Laura Cochrane on November 22nd, 2011 at 5:32 pm said:

I asked Ed Vogel, and he thinks this audio jack from Neutrik would work:

http://www.mouser.com/search/ProductDetail.aspx?qs=43pPWqpsSNu6OdPNfquEbw%3D%3D

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Goli Mohammadi on June 22nd, 2012 at 6:06 pm said:

Genius! Do you have pics of it posted anywhere?

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Damon on August 13th, 2012 at 9:11 pm said:

Just found this:
http://runoffgroove.com/faq.html

I’ll give it a try tonight.

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Gabriel Sharp on January 1st, 2013 at 4:24 pm said:

i made mine from parts of an answering machine someone threw out… 0$ spent

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Max on January 29th, 2013 at 3:51 am said:

The author used some parts he had lying around. The $5 was all he had to spend to get parts he didn’t have.

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