Introduction: The Process of Building a Cigar Box Guitar Amp - Little Gem or the $5 Crackerbox Amp
I have been an electronics hobbiest for several years, and there is something special about making musical toys. The most fun that I have is making Cigar Box Amps to sell locally, on Etsy.com, and sometimes eBay. I also run a website, tech-tut.com, that I try my best to describe what I'm doing and building. I'm finally attempting a highly detailed process that I can't exactly publish on my site, so here I am on Instructables. This is my first Instructable ever, and I value any feedback to make it the best it can be.
Building a Cigar Box Guitar Amp is not difficult, but it can be time consuming, especially if you want it to be near-perfect. Some things that don't always work out for me are the hole diameters and the occasional scratch in the soft wood of the cigar boxes. Even some of the nicer, tougher cigar boxes give way easily if your fingernail slides across the grains.
The time frame to complete a Cigar Box Amp ranges from a little over an hour to four hours depending on whether you have an assembly line or not. It also depends on the cigar box. If you have a thin box, it won't take you as long. Thick wooden boxes take longer to file the holes (unless you have potentiometers and jacks with long threads).
Overall, you will enjoy your Cigar Box Amp. Whether you buy one pre-assembled or built it from scratch in your favorite cigar box, you can expect that people will be impressed.
Step 1: Gather the Necessary Parts
This is the toughest part. You need to decide what you want to install your amplifier in. The easy choice for me is to use a cigar box, but Make magazine ran an article that used cracker boxes.
Next, you need to go shopping for parts. There are kits that you can buy with nice printed circuit boards out there. I've never used one because I like the "from scratch" method.
These are the parts from my latest Jameco.com order:
1-------------24133-------------------LM386-3 700mw opamp
1-------------140514-----------------100 ohm pot
1-------------29197-------------------5k ohm pot
1-------------281746-----------------stereo Switchcraft 1/4" jack
1-------------2006764----------------5mm blue LED (Everyone likes blue, right?)
1-------------23077--------------------5mm LED holder
1-------------1954818----------------speaker, 4-inch, 5w
1-------------690380------------------10ohm resistor (has to be bought in qty 100)
1-------------690865------------------1k ohm resistor for LED
1-------------30496--------------------220uF Electrolytic capacitor
1-------------93761--------------------100uF Electrolytic capacitor
1-------------43140---------------------perfboard or other circuit board
Grill cloth (Optional...find scraps of fabric locally)
Wire, solder, soldering iron, wire strippers, wet sponge, spray glue, hot glue gun, hot glue sticks, sand paper (220 grit works fine), rotary cutoff tool, drill and bits, hole saw (3-3.5"), drill press (optional), files, pliers, tape measure, calipers (optional), pencil.
The original circuit was labeled the "$5 Crackerbox Amp" in Make Magazine volume 9, but the parts order above is just under $30 buying the minimum quantities. You still have to find a cigar box and pay for shipping. :)
You may be able to find some of the above parts cheaper locally. Half the fun is shopping around for parts.
Step 2: Drill and Sand Your Enclosure
Your Cigar Box Guitar Amp is about to be born.
I'm going to describe my method using an imaginary 7"L x 7"H x 2.5"D cigar box. These dimensions won't exactly match the photos. Every cigar box is different, and the measurements that I make will not be the same.
Do a dry layout! Make sire that the parts will fit the cigar box.You also want to make sure that the controls and parts do not interfere with the closing of the cigar box.
I always start with the speaker location and work my way from there. I like to have the speaker at the "bottom" of the amp like most traditional, store bought amps. We are using a 4" speaker, so the center of the speaker is 2" from any edge. We will mount the speaker with the center 2.5" from the bottom of the cigar box (Be sure to factor in the thickness of the box side wood and add that to the measurement). The thickness of the wood on my imaginary box is .25", so I am going to make a dot at 2.75" (Measurement A in my drawing). Then find the center of your box. The center of my imaginary cigar box is 3.5" (Measurement B in my drawing). If the bottom left of the cigar box is the origin of an xy plane, the xy coordinates for this hole would be (3.5",2.75"). Use a punch or the tip of your pencil to bore a small divot so that your drill doesn't travel. Using a hole saw, drill a hole here.
The next holes to drill are for the LED, potentiometers, input jack, and voltage jack. In the drawing I have everything but the voltage jack on the "front" of the cigar box. I usually call the actual bottom of the cigar box the front. I evenly space them across the top edge of the front. Each hole is 1.4" (about 1 7/16") from each other. The outside holes are 1.4" from the edge. These holes are 1 - 1.5" from the top of the amp. You can be creative and put your parts wherever you'd like.
The final part to be drilled for is the power jack. You can put it on the side. Simply center it and drill wherever you please. Again, every cigar box is different, and giving you an exact measurement probably wouldn't work. For my imaginary cigar box, I will drill a hole that is at (3.5",1.25") with the corner of the side being drilled as the origin.
Drill each hole so that the parts fit using various drill bits. I use a stepper bit and then file the hole with a round file to get the final diameter. Dry fit all of these parts before continuing. Once the parts fit into their holes, sand the speaker hole so that it looks nice.Start heating up your glue gun!
Note: Be careful not to sand the outside of the cigar box. You only want to knock off the burrs left from the drilling process.
Step 3: Install the Speaker and Controls Into the Cigar Box
Dry fit all of the parts one more time before continuing. Visually inspect the box to make sure that the lid will close. If everything acts like it's going to fit, then set everything aside except for the box and the speaker.
If you choose to use a speaker cloth, now is the time to attach it. Spray a layer of glue inside the enclosure around the speaker hole. Cut a circle of cloth, and place it over the hole (on the inside of the box). Stretch it out so that it dries tight.
Next, put some hot glue on the corners of the speaker frame (on the speaker cone side) [Be sure not to get any glue on the speaker!], and press it to the box. Once it cools for a few seconds, apply more glue to the corners to get a good bond to the box. Once this glue cools, your speaker should not move.
Next, insert your potentiometers and tighten the nuts. Use a rotary cutoff tool to trim the 100 ohm trim pot shaft. It is too long. Insert your input jack and the voltage jack, and tighten the nuts. Finally, press in the LED holder. Insert the LED from the inside, and hot glue the LED into place.
Now, you are ready to make the circuit.
Step 4: Time to Make the Circuit and Connections
First, you'll need the schematic and layout. http://runoffgroove.com/littlegem.html
Start by placing the LM386-3 into the perfboard. Then populate and solder the parts around it in accordance with the schematic and the wiring diagrams. My drawing below shows you pretty much what connects to where.
Then follow the wiring diagram that I published on my website Adding a power supply to a Cigar Box Amp (REVISED) or the one at GeneralGuitarGadgets. Looking at both will provide some insight into the wiring of these circuits. I also drew a picture to give one more view to the wiring diagram and layout. The drawing below is exactly how I install my circuits.
If you want a printed circuit board, GeneralGuitarGadgets.com has one for $8. That's a little steep for me since I can populate and solder a circuit onto perfboard in under ten minutes. It's the wire connecting that will take a little longer. They do sell a 9v regulated power supply for $11 that is worth having.
After you solder the circuit board together you can make the individual connections to the controls. Following the various wiring diagrams that I've linked to should make it fairly easy.
[I feel as though this is cheating you! After publishing I realized that figuring out the wiring is still tricky! The next set of instructions is going to be full of step by step photos.]
Step 5: Step by Step Photos of the Installation (Wiring Diagram in Real Life)
The colors that you use to make this circuit don't really matter, but I am going to describe the colors to help make following this process a little easier.
Picture 1: The first step is to solder the negative battery wire (A) and a long black wire (B) to the tip terminal of the voltage jack.
Picture 2: Solder the positive battery wire (C) to the contact terminal of the voltage jack.
Picture 3: Solder a long red wire (D) to the sleeve terminal of the voltage jack.
Picture 4: Solder the long black wire (B) from picture 2 to the sleeve contact terminal.
Picture 5: Solder a 1k resistor to the LED's cathode. This is the end with the small indentation.
Picture 6: Solder a long black wire (E) to the other side of the 1k resistor.
Picture 7: Trim the long black wire (E) from picture 6 to the third terminal of the 100 ohm pot. Then solder two long black wires (F and G) to the same contact. Take notice of the pot's orientation.
Picture 8: Solder a blue wire (H) to the positive terminal of the speaker.
Picture 9: Solder the other end of the blue wire (H) from picture 8 to the middle terminal of the 100 ohm pot.
Picture 10: Solder a long green wire (I) to the first terminal of the 100 ohm pot.
Picture 11: Solder the long red wire (D) from picture 3 to the anode of the LED. Then solder another long red wire (J) to the same spot.
Picture 12: Solder the other end of the black wire (F) from picture 7 and another long black wire (K) to the negative speaker terminal. Next, solder the other end of the long black wire (K) to the ring terminal of the input jack. Finally, solder a long yellow wire (L) to the tip terminal of the input jack.
Picture 13: Solder a wire (M and N) to pins 1 and 3 of the LM386-3 IC.
Picture 14: Solder the white wires from picture 13 to the terminals of the 5k ohm pot. Solder wire (N) to the right terminal, and solder wire (M) to both the middle and left terminals.
Picture 15: Solder the long yellow wire (L) from picture 12 to the .01uF capacitor on the circuit board.
Picture 16: Solder the other end of the long green wire (I) from picture 10 to the negative end of the 220uF capacitor.
Picture 17: Solder the other end of the long red wire (J) from picture 11 to pin 6 of the LM386.
Picture 18: Solder the long black wire (G) from picture 7 to pins 3 and 4 of the LM386.
At this point, all of the wires should have a home.The next step should really make you happy.
Step 6: Finishing Up
Connect a battery to the battery snap, and plug in a guitar. The LED should light up.
If the LED lights, turn the volume and gain all the way up and play something. Does it sound right? Play with the volume knobs and make sure they work correctly. If it sounds great, then put a dab of hot glue on the circuit board, and glue it down so it doesn't flop around.
I used a piece of magnet wire to tie up the wires coming from inside the box to the lid.
Step 7: Plug It in and Play
You can add features like handles and decorations at this point. Search Google for cigar box amp photos. Join CigarBoxNation.com, and chat with other cigar box hackers. The Cigar Box Amp is just the beginning.
This is a video of me demonstrating my first 3/4w Cigar Box Guitar Amp. You can also check Etsy.com if you have decided that pre-made is the route for you.