DIY Matchbox Μicro-amp

Hello everybody, hope you're doing well

in this instructable, I m gonna show you how to make a simple matchbox µ-amp. So essentially it is a pretty simple and basic rechargeable loudspeaker in which all electronics components (except speaker) fit into a good old box of matches. It is also a simple project that is great for folks that are just starting to tinker with amplifiers because in its concept it is pretty basic and is almost completely made from recycled materials. I will also share with you some tips and tricks on how to make it louder and do some troubleshooting if you decide to give this project a go yourself. The plan was to make a portable phone amplifier that would hopefully be louder than the average smartphone speaker and fit it all into a small matchbox. I wrote hopefully because the speaker used in this project is pretty small when it comes to dimensions which means that there isn't any huge difference between the speaker used in this project and the average smartphone speaker. Because amplifier and circuit work well, the only component left that could make difference in sound quality is the speaker, so for better results use a higher-quality speaker. At first, I used a speaker from an old mobile phone, and while that worked I had quite a bit of distortion when the volume was turned up, so I replaced that speaker with a speaker from an old laptop which explains that If you see two different speakers on photos below so don't let that confuse you.

Box of matches

Speaker

PAM8403 amplifier

Charging connector

Rechargeable battery

Charging board

3,5 mm jack

Small switch

100-ohm resistors 2x

Spray paint (optional)

Superglue

Hot glue

Small piece of cloth (optional)

Wire

Tools Soldering iron, solder, hot glue gun, pliers, utility knife, and tweezers.

I would recommend you to use tweezers because the matchbox is a really small box and soldering some components in such a small box can be tricky.

List of components:

Box of matches

3.5 mm jack

Speaker

PAM8403 amplifier board

Small switch

Battery

Protection/charging board

Wire

Before I started working on my matchbox I spraypainted it.

I think that a 16340 Li-ion battery should work well for this project, If you wanna go smaller try a Li-po battery, but be more careful if you are using a Li-po battery.

In this step solder, the protection (and charging) board to battery terminals and that is it for this step.

Here I used the PAM8403 amplifier board, and the reason for that is that this is a class D amplifier that is pretty small in dimensions making it ideal for this kind of project.

What does it mean when an amplifier is class D?

In a nutshell, it means that in a class D amplifier amplifying devices operate as switches, and it also means that they have high efficiency. High efficiency is important here in this project because it means longer battery life. Note that this is a stereo amplifier, although in this project only one channel is used. This means that you need to convert stereo signal to mono signal. An alternative amplifier would be PAM8302 (mono class D amplifier), but you would still need to convert the stereo signal to mono. If you look at the PAM8403 amplifier board you should see some letters, they tell you what goes where.

L stands for left channel,

R stands for the right channel,

5v +/- stands for power supply input,

A symbol that looks like an upside-down T stands for ground and

OUT L and R stand for left and right output (this is where the speaker connects to).

In this step, I will show you how to recycle a 3.5 mm jack from old headphones and prepare it for the next step.

Start by cutting it off at a certain length, then remove isolation, when you do that you should find 4 wires and 2 of those should be the same color. Now all of these 4 wires have a thin layer of isolation on them and the easiest way to remove it is simply to burn it with a lighter, so one quick stroke over the flame should do the trick in this case. At this point, you should have 4 wires with isolation removed, twist together 2 of those that are the same color, and connect 2 100 ohm resistor to the other 2 wires ( 1 resistor at each wire), then twist other ends of resistors together and that is it :D.

Simply solder two wires before placing the switch into the box, this will make things easier in future steps.

Start by placing components inside the box to plan out the situation, also make two holes one for the charging connector, and one for the switch.

Place component, trace the outline with a pen, and then cut it out. Do this two times one for the charging connector and one for the switch.

The easiest approach would be to solder most of the components together before installing them into the box.

I wrote about connecting them in steps 3 and 4 but here it is to sum it up: Resistors are connected to the input of the amplifier ( so you need to pick which channel you would like to use either R or L here I used the Right channel of the PAM8403 amplifier), GND goes to GND, and power supply (in this case battery with protection board) goes to 5v. I connected - from the battery to - on the board and + of the battery on the switch and from the switch to the board. And lastly, the speaker goes to the output of the amplifier board (R out in my case).

Also, add a bit of hot glue to make sure nothing shorts out.

Trace the outline of your speaker, and then cut a hole in the box of matches.

Because this kind of cardboard is pretty thin I would suggest you to cut out a speaker hole with all electronic components in place.

Close the box of matches and pull two speaker wires through the hole (these are two wires from the output of the amplifier board) and then solder the speaker to these two wires. And if you are wondering where you can find a small speaker for this project, try looking at some of your older phones (or eighter tablet, or a laptop maybe). As I mentioned before at first I used a speaker from an old phone and while that worked I had quite a bit of distortion when the volume was turned all the way up, and a better speaker solved that problem, so I got that speaker from an old laptop. I simply cut it out of its speaker box using wire cutters.

Now to secure the speaker in place use hot glue. Wrap the speaker in some cloth, place it on the speaker hole then hot glue it in place. Hot glue works really well here because the matchbox itself is pretty thin and if the volume is turned all the way up there would be some kind of rattling sound because both speaker and box vibrate and bounce out of each other, but that problem is gone when the speaker is glued firmly in place with hot glue. And now the box of matches acts as a speaker box.

The ending result is pretty decent, What I mean by decent here, in this case, is that it is easily as loud as an average smartphone speaker with few hours of playtime, and don't expect that if you make one of these that you're gonna have Hi-Fi sound, but if you use a decent and more high-quality speaker, and if you do it right you could have great results.

For some reason or other to me, it looks like some toy made in the 1940-s, and don't forget that a striker still works :D.