Ep. 36 | A Bluetooth speaker bought for under ¥1 sounds amazing after the mod! A junkyard speaker turned into a wireless Bluetooth speaker — the result is a real surprise

¥1 junkyard speaker turned into a wireless Bluetooth speaker: the original amp board won’t amplify the Bluetooth signal, so the Bluetooth board drives the speaker directly + 6 × 18650 cells

An old powered speaker picked up at the scrapyard (under ¥1); fuse good, a hum on power-up, transformer output normal. The plan was to feed the Bluetooth module’s audio output into the original board’s audio input, but it didn’t amplify; switched to driving the speaker straight from the Bluetooth board, which works. So everything original except the driver comes out and it becomes rechargeable — 6 × 18650 spot-welded into a pack with a 3S60A balancing BMS, fish paper insulation and fibre tape; a diode and a CC/CV buck module on the charge side; a fast-charge port, charge-level display module and switch in the case; wired up, powers on, back in the case, phone pairs and plays, ‘sound quality is decent for its size’. The top comment points out that without audio amplification the result is only so-so.

Outcome

Steps8 steps · click a frame to jump

1. 
   1. Found the speaker, check the fuse and power it up

   An antique powered speaker for under ¥1; the fuse is external and easy to get at; multimeter says the fuse is fine; power it straight up — no smoke, a hum from the driver.

   00:00 – 00:27
2. 
   2. Open it up: transformer output is normal

   Simple layout: transformer + a single-layer board (audio amp circuit), no burn marks, transformer output voltage normal, so in theory it works; there is also a small chip on the board.

   00:27 – 00:56
3. 
   3. Pull the Bluetooth module from a hoverboard speaker, feeding the original board fails

   The Bluetooth module has just two pairs of wires, wide-range DC input and audio output; feeding its audio output into the original board’s audio input doesn’t work — the original board isn’t a plain audio amplifier.

   00:56 – 01:24
4. 
   4. Drive the speaker straight from the Bluetooth board, strip out the original parts

   With power on the Bluetooth board pairs and can drive the driver directly; so cut all the wires, keep only the driver, drop the mains supply too, go fully wireless, and fit a quick charge port.

   01:24 – 01:56
5. 
   5. Build and spot-weld a 6 × 18650 pack

   Lay out holes in the case for the charge-level display module and switch; prepare 6 × 18650 for the pack and spot-weld it.

   01:56 – 02:14
6. 
   6. Fish paper insulation, connect the 3S60A BMS

   Wrap in fish paper, solder the BMS balance leads and + / − leads, check the wiring with a multimeter; fish paper + fibre tape at both ends; wire + and − to the input side, diode on the positive, CC/CV buck module on the charge side to protect the cells.

   02:30 – 03:02
7. 
   7. Fit the charge display and switch, tidy the wiring

   Quick-port charge lead to the buck module input; charge display module and switch into the case holes; switch output positive to the power input lead with a thin branch to the charge display; charge display negative tied to the Bluetooth module negative; BMS output to the switch input positive and main negative.

   03:02 – 03:44
8. 
   8. Power on, back in the case, play over Bluetooth

   Switch on, lights up fine; pack, CC/CV module and Bluetooth module go into the speaker case, plug in the driver lead and Bluetooth power lead, screw it shut; phone pairs and plays, sound is decent for its size.

   03:44 – 04:23

Bill of materials

Measured on camera

Creator’s tips

• An old speaker’s amp board won’t necessarily amplify Bluetooth audio; if it doesn’t, use the Bluetooth board’s own amp to drive the speaker directly 01:24
• Once the BMS is wired, check the wiring with a multimeter before closing the case 02:48

Pitfalls

• Feeding Bluetooth audio straight into the original board’s audio input doesn’t work (it isn’t a plain amplifier) 01:16

Li-ion safety

• Fish paper + fibre tape at both ends of the pack 02:48
• Diode and CC/CV buck protection on the charge side 02:56

Quotes

Cost & time