100W DIY Bluetooth Speaker

Thrify Upcycling for Portable Sounds

Daniel Bisegna

Issue 1, July 2017

Using a handful of cheap parts and some nifty recycling, Daniel has created a powerful Bluetooth speaker that’s totally portable, extremely cost-effective, and outperforms many of the more expensive units.

We’ve all seen them in shiny boxes on the shelves of our favourite stores. Unfortunately, the cheap ones are usually “cheap” in every sense of the word, with poor sound quality and speakers that are often undersized. This one boasts a powerful 100W amplifier module, 100W 4Ω coaxial car speaker, in an ultra-compact package. 

Thanks for taking the time to show us your project, Daniel. What made you want to develop your own Bluetooth speaker?

I wanted to build a Bluetooth speaker because I enjoy creating small electronic projects, but have not yet created something practical enough that I would use on a regular basis. After some thought, I decided that a Bluetooth speaker would not only be something that I would use regularly, but it would also challenge me and develop my DIY skills. After finishing this, I now want to take on a more advanced project in the future.

A cost effective car speaker

You’ve made great use of an off-the-shelf car speaker. Did you have it already or were they purchased specifically for this project? 

The car speaker I used was the Audioline 4” 2-way car speaker, which I bought as a pair from JB Hi-Fi, for $27. I did have recycled speakers at home that would have done the job, but I wanted the unit to look its best so I went with a brand new speaker to add to the overall aesthetics. I will potentially use the second speaker in another Bluetooth speaker project.

At $27 a pair, that’s a bargain anyway, and you’re right – we always want our DIY projects to look great! What amplifier module are you using to help wind up the volume? 

The amplifier board is the TPA3116DA, which I purchased from eBay for $17. It’s a 100W single channel amplifier that can be powered by a 12-24V supply (although 9V from a battery will work at a reasonable volume). The board is small, has an adjustable gain control and a big heatsink, making it perfect for this project. With lower voltages, it will distort at high volumes, but my speaker can be powered with either a battery or DC input, meaning it can reach considerable volumes with a power supply.

The distortion is understandable at low voltages; you’re not trying to match a 1000W Hi-Fi system with it, after all. 

The Bluetooth module I used was a simple USB-powered Bluetooth audio receiver I found on eBay. It is powered by 5V USB and outputs to a 3.5mm AUX. To power this, I used an old broken car Navman 5V power supply. This allowed me to get a 5V supply from 12-24V and I used the power light for the power indicator on the speaker itself. I soldered the 5V output to the USB contacts of the audio receiver, and stripped an old AUX cable to get the audio output. 

Note: The original one I purchased is no longer available but it’s similar to the one you’ll find on eBay.
Making it all fit
Bluetooth Internals

That’s a great way to get a 5V supply. I think we’ve all got a few of those unused in-car gadgets lying around. Running from 9V batteries is a great idea to keep it portable. What sort of run time does it provide? 

When deciding to power the speaker, I opted to wire the batteries in parallel to increase the running time. I have not yet done any testing on the speaker but it ran on an old 9V battery from a smoke alarm, for at least an hour at about half volume. I plan to conduct running time tests in the future. One modification I am starting to make on the speaker is a switch that will allow you to switch between a parallel and series circuit, so you can choose between one battery for 9V or two batteries for 18V to provide louder volume. I predict that with one fresh 9V battery, the speaker will easily last a few hours at about half volume with Bluetooth on.

Interesting idea. I don’t doubt you’ll be able to get more distortion-free volume, even if it’s at the expense of some run-time. Can you take us through your custom back panel?

The back panel is rather confusing, so I plan to add labels in the near future. I need to figure out a way to make them look good without simply using white paper print outs. On the right is the DC input socket, which is a standard DC plug, allowing me to use small DC packs or even laptop power supplies for really high volumes. Next to this is the power indicator LED, and below it is the three-way power switch. Switching it up uses the DC input power, switching it down uses battery power, and in the middle turns it off. Next to this is the Bluetooth switch, where the up position turns it off and the down position turns it on. On the left is the AUX in socket and the volume control. 

The box construction is very neat. Was it purpose built or reused from something else? 

The box I used for the speaker was from an old broken toy guitar amp, which was given to me by a friend after he found it under the bed. The unit originally ran on two 9V batteries, making it easy for me to power my project with the same power source. The original circuitry inside was bad and did not work, but I could have reused the speaker inside. Instead though, for the sake of aesthetics and sound quality, I opted for the store-bought ones. The front cover and back control panel of the speaker have a carbon fibre texture. I bought this on the internet for about $4 for a 30cm x 1m roll. This stuff feels very similar (and probably is) to the contact you might use to cover a school book. I used a hair dryer and a lighter to soften the material on the back, enabling me to poke holes through it so as to put the switches and sockets in. The unit now weighs 1.4kg overall, including the batteries.

That’s an amazing reuse of a suitable enclosure, which is sometimes the most difficult part. It also explains the selection of 9V batteries, which aren’t an obvious choice right away. With all the parts recycling you’ve done for this project, was it a cost-effective project in the end?

Absolutely! Once I had all the parts for the project, it took me about four or five hours of wiring, soldering, and re-soldering the innards together until it was finally complete. The total cost of the project was as follows: [editor's note: prices may have changed]

•    Box: $10 (Old,from a friend)
•    Speaker: $27 (for a pair)
•    100W Amplifier Module: $17 (Now selling on eBay for $12)
•    Bluetooth Module: $5
•    I already had all the wiring and switches

This makes a project cost of just $49. In comparison, similar speakers on the market that can reach similar volumes can sell in upwards of $200, so I believe that this project was not only a really fun way to improve and develop my DIY electronics skills, but I’ve also saved myself hundreds of dollars for the same (if not better) result. 

That’s awesome! What a successful project, for so many reasons! If you were to build a second one, is there anything you would change?

If I were to build a second speaker there would be a few things I would change. Firstly, I would make my own box for it. I got lucky that a standard four-inch car speaker fit perfectly into this one. But with a custom built box I would be able to make a speaker fit very well, with adequate space allocation for the amplifier and batteries. The configuration of this box almost forced me to use 9V batteries for power, as the battery compartments were cut out of the back panel. They also took up space inside the unit, which prevented me from using different batteries. This leads me to the second change. I would like to have had built-in SLA or 18650 batteries to power the speaker, as this would enable me to make a completely portable speaker with rechargeable, self-contained and more powerful batteries. I would also like to add a microphone system with a receiver to the speaker, so as to make it a portable PA system, and not just an audio player.

They sound like some great upgrades for version two! Thanks for taking us through your DIY Bluetooth speaker, Daniel. We’re looking forward to hearing about your next creation.