It seems like only yesterday I started playing the guitar: my mother bought me an acoustic for about 15,000pts (about 90 ? from today) and at that time I didn’t know a single chord. I started to learn classical guitar, but what I liked was bands like Nirvana or MetallicA. It wasn’t until about 4 years later that I had (and still have) my first amp. It was a Fender that was priced out of my month’s salary at the time, about 80,000pts (about $500 now). In those four years I missed having an amplifier to be able to play with “electricity”.
Today there are many more options. In fact, I don’t use my amp anymore. Instead, I connect my instruments to multi-effect pedalboards that go straight to the computer, where I can record and edit whatever I want. But how much are those footswitches worth? There are many prices, but I have two that once cost me between 300 and 500 euros. I explain this because it’s clear that ‘one of the problems of wanting to play with an amplifier is the price of this one or the devices that replace it. In this article we will show you how to create the cheapest mini amp you can imagine.
The cheapest amplifier you can imagine
All we’ll need to create this mini-amplifier will be:
- An LM386 chip ().
- A 9V battery. The “flask” of a lifetime.
- Some Perfboard. You have something in THIS LINK, but that one already exceeds the promised price. If you have something from an old device you can use it perfectly.
- A resistance of 10 ohm.
- A 10k potentiometer ().
- Some old headphones.
The first thing we’ll have to do is manufacture the circuitry. We’ll do it without soldering anything, and if it works, we’ll solder everything. The intention is to check first if it works and then give the last touches to the board. If we rush to solder and something goes wrong there will be no turning back. Also, when welding, we can go too far, break something and not know what has caused the failure, if a bad assembly or when welding.
The LM386 chip’s instruction sheet already has some examples of how to create amplifiers, so we don’t have to get too hot in the head. We will have to take the first example, the 20 gain amplifier. The chip diagrams can be a bit confusing: the triangle represents the 8-pin LM386 chip in the center of the circuit and the chip design is anything but triangular. The pins are numbered around the chip from 1 to 8 as shown in the picture below. IMPORTANT: Unless otherwise stated in our instructions, the measurements are in inches.
We will have to alter the capacitor values to get as close as we can to the standard values. We will use a ceramic capacitor from .047μF and an electrolytic capacitor from 220μf instead of the values we see above. In the following picture, the two batteries on the left would be replaced by the 9V battery.
In the following picture we see a small speaker from a compact board. We can use any 8 ohms speaker.
Then we have to put the components in the perforated material and bend the wires to form the circuit. Here we have to take into account that we have to leave enough space to fit the 9V battery, the biggest component by far. If we use a larger speaker, we can simply put the mini-circuitry at the back or opposite of the speaker.
Where to use this amplifier
We can use it in any project where we need to amplify the sound, like a headphone preamplifier, a portable guitar amplifier, a portable MP3 player speaker or even to do robotic voices. Of course, the sound delivery will never compare to a quality speaker worth hundreds of euros.
In this article we are talking about using it as a guitar amplifier. If we are going to put it in a metal box, we will have to cover the walls with some kind of insulation. It’s clear that 9V won’t kill us, but it’s likely that we’ll get some kind of cramp that will make us feel like a little prick. Besides, insulating it will also come in handy so that the dirt doesn’t deteriorate our new creation.
Below you have several images of the printed circuit board. Labels and traces have been added to help with the assembly. Please note that the audio input cable of our headphones will be soldered directly into the potentiometer hole.
To use it as a guitar amplifier, all we need to do is to connect the 1/4-inch jack to the audio input. As soon as we solder it, any standard electric guitar cable will work. The result is shown in the following picture. We have used a box of Altoids pickups, which are like the famous Juanola we have in Spain but with a mint flavour. I think it’s important to mention that we have to be careful with the 1/4 jack port because if we bend the inside part we can cause it to sound bad, which it doesn’t usually do, or we can hear very annoying interferences.
The decoration must also be taken into account. Because of its size, we can fit this mini-amplifier almost anywhere. If we are going to use it as a speaker, I have seen this amplifier placed inside a hollow book where an MP3 can also be placed. On the other hand, it is also possible to make a box with LEGO parts, which would give it a more “geeky” image while avoiding the problem of small cramps, which are not dangerous but can be annoying.
How about this world’s cheapest mini-amplifier?