Introduction: Built in Ukulele LM386 Amplifier and Speaker
The LM386 is a great little all-around amplifier that can be used for music and guitar amplification. I decided to install one in my beater tenor ukulele so that I could amplify the preamp pickup built into my uke, or amplify a removable piezo pickup that I can easily put on and take off my uke, or use the ukelele as a stand-alone amplifier for my phone or guitar.
I discovered that by adding the amplifier to the ukulele it gave it a much brighter and pleasing tone. Now when I play the uke with the amp turned off, it sounds very dull to me.
This project only requires a hand-full of inexpensive parts:
LM386 kit - about $1.50
1/4 inch jack - $1.00
Speaker - salvaged from broken bluetooth speaker - about $2.00 if bought new
On/off switch (spst) - salvaged or $1.00 new
9volt battery and box - about $2.00
Buying a comparable micro-amp would run you $30.00 or more and building your own is a lot more fun.
The LM386 is surprisingly powerful as it can boost the input signal up to 200 times.
In the future, I want to try some other cheap amps that are even better than the LM386 and also some other speakers and transducers. Perhaps I will even paint my ukulele to cover up the scars resulting from experiments past.
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Step 1: Build the LM386
You can buy the LM386 as a single IC or a kit or pre-built module. I bought the kit cause they are fun to put together and only take about half an hour. Mine came with no instructions but you just insert the components into the marked holes on the circuit board and solder them and as long as you don't put the capacitors in backward, you are good to go.
The amplifier is great as it is for a low-impedance input device like a pre-amplifier or piezo contact transducer pickup for a stringed instrument. If you want to use this amp on a high-impedance input like an electric guitar then you probably want to build the Ruby guitar amplifier which is well documented here: https://www.electrosmash.com/ruby-amp-analysis and other websites that show how to match the electric guitar impedance to the basic LM386 amp.
Add an on/off switch (SPST) between the 9-volt battery positive terminal and the amplifier VCC in terminal.
The speaker can be a 4 ohm or 8 ohm speaker.
Step 2: Modify Your Ukulele to Mount Amplifier Parts
1. Speaker hole: You need to mount a speaker somewhere. Where I mounted mine is ok but I wish I had put it lower down so that my arm would not cover the speaker. Probably losing a little volume because of that. You must also be aware of the bracing struts inside the ukulele or guitar before you make your holes. I messed my first hole up for the amplifier potentiometer because I drilled through a strut and that left no room for the potentiometer shaft to poke through.
I cut the hole, very crudely, with a utility knife blade. You can get nice little hole cutters to make a cleaner job of it but it is hidden beneath the speaker anyway so it doesn't matter to anyone except perfectionists.
Also, you should have a grill of some kind to cover the speaker as it is easily punctured. Mine is held on with a couple of magnets to the speaker rim. I tacked the speaker itself to the ukulele with a couple of dabs of hot glue. Doesn't take much to hold it into place.
2. Amplifier volume control shaft: I mounted mine in an awkward position under my arm. Should also have mounted in further down so that it could be easily adjusted.
3. Battery box: I mounted the battery box on the backside and that seems to be a good place for it. I don't think that making it a part of the back of the uke affects the sound adversely. Battery positive lead goes to the switch and the ground lead goes to the amplifier. Also, cut the hole using a utility knife blade.
4. Input jack: use a mono 6.5mm (1/4 inch) jack and connect it to the LM386 input pins.
Step 3: Using the Amplifer
1. You can use the ukulele amp as a stand-alone amplifier for music or as an amp for another ukulele or guitar.
2. If your uke or guitar has a pre-amp built into it then you can run the pre-amp out into the amplifier input with a guitar cable or pedal cable like I do.
3. You can use an external transducer or surface mount pickup and input that into the amplifier input.
4. You can use the pre-amp output or a transducer output jack and run that into some effects pedals like a looper and run the looper output back the ukulele amp input.
Step 4: Future Modifications...
1. There are some really really cheap and nice amplifiers out there that can be used in place of the LM386 and which will probably do even a better job of amplification. The LM386 only outputs about a half-watt of power while the PAM8403 outputs two 3 watt channels of power. I think that will be my next project as they only cost a couple of dollars.
2. I could probably find a better speaker than the one I used. You can use 4 or 8-ohm speakers. The LM386 will easily drive a 12-inch speaker though it won't rattle the timbers.
3. It would be nice to try a ToneWoodAmp effect by using some vibration speakers.
4. I want to plug in a looper pedal between the uke pre-amp the uke amplifier. WIll require purchasing a looper pedal and two guitar cables.
5. I wonder what effect would happen by covering the ukulele soundhole? WIll more volume and pressure come through the speaker or does the uke require some sort of air-hole?
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