In this instructables I'm gonna share the process by which i developed my small guitar amplifier (actually i'm not a guitar player, but I called this project like this because of the appearance of the mini amplifier, so it can be used as a general purpose amplifier as well).
My main intentions were to keep it as small as possible without sacrificing the sound quality, to make it looks like vintage and to turn it into practical and affordable. So some features couldn't be included in it, as sound distortion for example.
This project requires little electronics skills, since the amplifier circuit is pretty simple (thanks LM386), and a bit of wood working skills, since the box isn't that complex at all. I'll give the measures I used in the case of my amplifier, but actually it's up to you, since the design isn't the most important aspect of this project.
So here goes the list of components I used for the electronic part:
- 1 LM386
- 1 resistor of 10kOhms
- 1 resistor of 10Ohms
- 1 electrolytic capacitor of 220uF/16V
- 1 ceramic/polyester capacitor of 33nF
- 1 ceramic/polyester capacitor of 47nF
- 1 potentiometer of 10kOhms, if possible with switch
- 1 jack plug(P10)
- a 2´1/2 speaker - 4Ohms
- a 9V battery plus connector or a 7.4V lithium battery
The most expensive component is the speaker, and I used a Sony one, but it´s not necessary to do so, I just chose this one because there are few options of 2´1/2 speakers to buy, and because the sound quality of this speaker is simply amazing, but any brand of speakers is fine since it fits the project.
Step 1: The Case
The case is pretty simple, and can be done with plywood or any other kind of wood. I used some pieces of wood I had at home, I don't know what kind of wood it is, but it's not important at all.
I used some screws and wood glue in order to unite all the parts of the box, but maybe just the wood glue is enough, I would just recommend the use of screws in the bottom of the box, because then it's possible to take the speaker out of the box easily.
As a suggestion the box can be covered with those fabrics that are used in common amplifiers, or maybe painted with some kind of varnish.
The measures are specified in the PDF file (on the bottom of the page), some measures can be different according to the speaker or maybe the kind of wood you are using, then just make sure to fit them to the materials you are got.
It's not necessary to use the same materials and components that I'm using, so some characteristics can be a bit different. what I mean is that you don't need to buy new materials since you already have some that can fit the project pretty well.
Because I also did this, I just grabbed some stuff I had at home, put everything together and then the Mini Amplifier was born.
Step 2: The Circuit
Since I'm using the LM386 the circuit is pretty simple, and can be found in the datasheet of the LM386, I used the circuit of BASS BOOST, I know that the sound of the guitar is based on high tones, but as I said in the beginning this is actually a general purpose amplifier, so if you are planning to use it as a guitar amplifier just change the circuit for another suggestion in the datasheet.
In bottom of the page the PCB that I used is available, it's really small and fit the case pretty well (of course), but remember that is the bass boost one, so if you want another circuit, just ask me that I can do that for you (of course, in my free time).
Step 3: The Front Panel
The front panel holds the potentiometer and the P10 connector, I haven't done a PCB for these parts, because I couldn't find the datasheet of the potentiometer, since I took it from an old board found.
The potentiometer already has a switch in it, so I'm not using an extra switch, but as it's hard to find these potentiometers, if you don't have one, just include a switch in the front panel, and a led as well, if necessary.
The wiring process is simple, just make sure that the soldering is well done, in order to avoid noise and bad quality sound, it's also interesting to use thermo retractable sheath in the terminals in order to isolate all the wiring and the soldering connections.
The central pin of the potentiometer is connected to the SIGNAL IN ( identified in the PCB as a S), the extremity pins, one is connected to the GROUND (that is also available in the PCB) and the other one to the P10 connector (but pay attention, because it must be connected in the positive or the signal part in the P10 connector, as specified in the picture below), and finally the negative (GROUND) part of the P10 connector must be connected to the same ground of the potentiometer.
***Pay attention while connecting the extremities of the potentiometer, else the increase/decrease function of it, can be inverted (considering the pattern that is commonly followed), if you don't mind about it as me, that's not a big deal, but if you prefer in the "right" way take care while connecting it.
Step 4: Putting Everything Together
In this part all the parts will be connected, just remember to be stingy while connecting all the in order to avoid miss connections, that are able to damage the circuit or maybe the speaker, so double check all the steps and pay attention to every single detail.
There is also a video showing the parts of the mini amplifier, so if you are interested in doing it just check the video.
Step 5: Testing
So the video ilustrate the performance of the mini amplifier, there is a part in the video that a failure in the sound ocurred, but that is because of my microphone, the amplifier is sounding pretty well.