Make your own wireless Bluetooth audio amplifier to use with any set of speakers!
Hey everyone, Tom here, and today i just want to quickly show you this little battery-powered, 3D printed bluetooth audio amplifier that i made and kinda explain the design choices behind it. Now, this video is more of a prototype because i didn’t really plan on making a video on this project specifically, so i don’t really have any footage of the process, but future project logs will of course be a bit more fleshed out in that direction.
So the reason why i built this thing in the first place was to have to have a small, completely wireless, well, except for the speaker cables, audio amplifier that can be easily taken to another room or just sit in one space and provide an easy way of listening to some music without having to plug in my phone or any other device. And because you can plug in any type of real speakers, you’re not limited to the processed sound those little Bluetooth boomboxes produce.
There is no on/off switch, so to turn it on, you simply slide in a battery. These are Sony NP-F compatible lithium batteries, which are used in a lot of prosumer video equipment like lights or in my case, also in my teleprompter. I’m also planning on getting a few more of these batteries to make my Printrbot Play completely battery-powered as well. These batteries are great because they are relatively inexpensive, very common, pack a lot of capacity even though they do come in different sizes, and they already have all the necessary protection electronics built-in, so you don’t need to worry about too deeply discharging the battery and ruining it that way. They deliver 7.4V nominally and this one lasts for about 65 hours of continuous runtime with this amplifier at a medium volume. But this little thing can actually deliver quite a bit of power to the speakers if you wanted.
There’s a 2x15W stereo class-D amplifier in here, which, again, is super cheap and very efficient, so it doesn’t really put out any heat in the amplifier itself. Bluetooth functionality is handled by what used to be a USB-powered Bluetooth audio receiver, and i’m simply powering that off of a LM7805 linear regulator with a few tiny capacitors between its legs to get a clean power supply for the receiver. When it comes to the power for the amplifier itself, that voltage is boosted to 12V with a small step-up converter, so that the amplifier has as much headroom as possible to reduce clipping at higher volumes. You could also directly power the amplifier from the battery, but you’d be limited to about one fourth of the maximum usable volume. And one last detail is this LED voltage monitor on the front to keep an eye on the charge level of the battery. With these huge batteries, this isn’t really necessary since you literally won’t run out of juice for days, but it’s a nice touch nonetheless.
Now the nice thing about this case is that it’s only two parts that are screwed together with M3 cap-head screws. This bottom part has a few vent holes as well as mounts for the LED voltage meter and the speaker terminal, while the top part is essentially only a lid with a battery mount. The battery contacts are simply these 2.6mm plugs that are apparently commonly used for model trains, but they also fit perfectly into the batteries and when you take them out of their housing, you can simply solder in a wire and then super glue them into the battery holder. There is no battery retention or lock here, and while it would be fairly simple to implement, but isn’t necessary since the battery stays in place quite well by itself.
So for wiring everything, it’s super straightforward. The positive and negative battery terminals go to the LM7805 regulator for the receiver and the step-up module for the amplifier, then the 5V output from the linear regulator goes straight into the receiver at the back of its USB connector, while the 12V from the step-up go to the amplifier. The LCD voltage meter is also directly connected to the battery. The audio output from the receiver is directly wired to the amplifier and the output from there over to the speaker terminal. Adding in a few capacitors to the individual supply voltages can’t hurt, but in my case i was happy with the result as-is. All the modules were simply glued in place with some hot glue or superglue for a bit of a more permanent result.
Now, it’s not perfect, for example it doesn’t have any volume controls in the amplifier box itself, since i wanted to keep it as simple as possible, but it would be trivial to add a potentiometer between the receiver and the amplifier module. As it is now, i can simply adjust the volume on my phone. Also, as long as there is no audio being played, there are some slightly audible noises, but once the audio actually turns on, those are completely gone.
I generally like to build my projects with modules like these to keep them flexible and modular. I keep a stack of standard-function modules around that allow me to quickly throw together quite a few different things. You could also go with an integrated bluetooth receiver and amplifier, those often also have buttons for next or previous track and for play/pause, and while i’d think they wouldn’t have the slight noises this solution has, they are also more expensive and less flexible.
So that’s just a quick overview of this project, i think it turned out pretty nicely and the best thing is, the parts in here only cost a bit over $10 with free shipping as most of these components are very common modules that you can cheaply buy from overseas. I’m happy with the results and might even end up making another one. If you want to make one, too, i’ve put links to all the components in the video description as well as to the files for the case.
So thanks for watching, again, there will be project logs that are a bit more complete, so get subscribed or you might miss them. Anyways, that’s it for today, see you in the next one!
Music is Something Elated by Broke For Free, licensed CC-BY 3.0