bluetooth boombox
creative
technology
The photo above is of my 1980’s era boombox that traveled with me many places playing the Red Sox on the radio and cranking music from cassette tapes..
These days it’s my Bluetooth speaker that hits the road with me, but I would rather not bring it to the beach or have it sitting on the ground next to a fire pit. That kind of terrain is for my rugged boombox.
A goal of this project was to perform the minimal possible modifications to the boombox while converting it to Bluetooth. YouTube is awash with instructional videos on how to convert a boombox to Bluetooth. Many of the instructors perform the conversion with no regard or respect for the original hardware. I even watched one where the first step was to “pull out all of the circuit boards and stuff”. Savages.
I was not looking to convert any old boombox, I was looking to convert my boombox.
The only modification to the origianl hardware I made was to cut part of the plactic divider that seperates the top and bottom row of D size batteries to fit my 12V Li-ion power bank.
As long as the battery pack is switched on, all I have to do is set the switch to LINE-IN, pair my phone and I’m good to go. I still have the option of listening to broadcast radio.
The boombox runs on 12V from 8 D size batteries. The first stroke of luck on this project was that there were 4 fresh batters in the battery compartment. Remarkably, I found 4 fresh D batteries in a kitchen drawer. I took that as a good sign.
Eventually I would have to power the boombox off a 12V battery but using the D batteries to power the unit while powering the Bluetooth receiver with the USB output of the 12V gave me time to put the hardware together before deciding on the final placement of the components. With this setup and the output from the BT hooked up to a Y-cable into the RCA LINE-IN inputs of the unit everything was great.
To power the boombox with the 12V power bank without altering the unit I 3D printed a brace that is held in place by the battery spring. It jams L-shaped pieces of metal against the batter plus and ground, wires soldered to them conned to 12V.
The BT receiver I purchased needed an amplifier, so I built two mono amps on a breadboard using LM386 ICs. A 5v regulator powered the amplifier and BT module. That’s when the trouble began. With separate power supplies the sound was crystal clear. Powering everything from the same supply introduced tons of noise on the output.
I told myself, without really believing it, the problem was due to the amplifier being build on a breadboard instead of soldered together. Eventually I was able to eliminate almost all the noise, fist by the judicious placement of capacitors then by the willy-nilly placement of capacitors. Still there was one small but very annoying ffffffttttt sound whet from silence to music.
All noise problems were solved by purchasing a BT receiver with a built-in amplifier. I soldered up a circuit board with 12V coming into it, 12V going out to the unit and a step down buck converter which sends 5V to the BT receiver. The left and right audio outs from the BT receiver are soldered directly to the internal LINE-IN connections. Custom brackets hold the circuit board and the BT receiver solidly in place, ready for the road.