Introduction: Little Gem Guitar Amp, Cheap and Easy to Make
I thought I needed a small portable combo and I found out about the Little Gem project and thought that would be a perfect project to complete with my kids. They are 7 and 9 and did some of the soldering in the first of the two combos, the red and blue box.
The components should be cheap and easy to find and I saw more builds here on Instructables though those where a bit more complicated and had a bit more finish than I was looking for and I wanted to show how easy it can be if you want it to.
The best thing would of course be to use a proper circuit board but I used a piece cardboard.
I also made it so that disconnecting the guitar cable will cut the power so no need for a power switch or a led to indicate that it is on. Also I only use it with an electric guitar that has a volume pot so no need for a volume pot on the amp.
It has a power jack that disconnects the battery when a cable is inserted.
Step 1: Get the Stuff
- LM386 24133 - 173045208
- Pin IC Socket 112206 - 14813549
- 5k ohm pot 29197 - 16425375
- Stereo jack, 1/4" (I used a switched one) 281746 - 14276004
- Knob (optional) 264946 - 13818606
- Battery snap 216452 - 14204202
- Speaker10ohm resistor 690380 - 16012256
- 0.047µF / 47nF capacitor 1947351 - 16522635
- 0.01µF / 10nF capacitor 15229 - 16586614
- 220uF Electrolytic capacitor 30496 - 16715486
- 100uF Electrolytic capacitor 93761 - 16586614
- Voltage jack 151590 - ?
- Circuit board
As described at electrosmash the pot could be changed to 2k or 1k to increase responsiveness of the gain control. On my amp I use 5k and nothing happens til about half a turn.
I think you should be able to use any stereo jack, the idea is to have the signal on the tip and let the ground go on ring and sleeve. That way when you connect the guitar cable (that normally is mono) the ground will be connected to the circuit board.
You can use any size speaker really, most builds I've seen use 4" speakers but I had pair of 6.5" left over from a car so I used them, the smaller the speaker the smaller the combo naturally.
You can use any enclosure you want, some use cigarr boxes, I chose stuff I found at work. One combo is made from a dishwasher tablet box and the other is a carrying case for a label machine that I cut out the lining on one side.
Step 2: Optional, Place the Speaker, Pot and Jacks First
This step might be best to do first so that you get the correct cable lengths from the start, it is also easier to solder if things are mounted to something. If you have a small box and can not access things easily you can solder first and mount later.
Step 3: Place the Components on the Board
This is one way of placing the components, one important thing is that the 10 Ohm resistor and the 47 nF capacitor should be placed as close to the chip as possible to avoid oscillation.
The long pin on the electrolytic capacitors are positive and there should be a white line on the side (and possibly even "-"-marks on the negative side.
The other two capacitors are non-polarized and can be mounted either way.
You can push the chip in socket now if you want, the dot on the chip goes the same way as the notch on the socket.
Step 4: Solder
Flip the board and solder, this picture shows the components from under the board. I followed another guide that did not have this view and that made it harder to follow for me.
Don't solder "on the fly", that will make for bad connections. Make sure both ends that are to be soldered are stable and will not move while you solder and for some time afterwards while the solder cools down.
Step 5: Done
They sound quite allright, maybe another speaker will sound different but mine has a bit of bass, you can fell the vibrations in the floor. The distortion you get from turning the gain up is not the best but with a battery driven pedal you have a rig that can be carried and played walking around with the amp in a backpack.
In fact, my son uses the one with the red and blue box around the house and he also took it with him when he went to visit a friend. Very portable.