Wednesday, July 29, 2015

Bluetooth boombox project

Good day, worthies.

Ok, here's the promised followup.

Pardon my messy workbench!

Here we see my test setup for a bluetooth boombox I've been considering for the last couple of months. I had originally planned to roll my own amplifier board based on the TDA2050, but ran into technical problems while etching the board. (My photoresist developer solution wiped the entire design off the copper sheet. What a letdown.) So, in a fit of despair, I ordered a Nobsound GFB646 amplifier board from Amazon. This board uses a TI TPA3116 Class-D amplifier to provide 2x50W. It also includes a Bluetooth receiver and integrated volume/treble/bass controls. I will probably write up another post containing my thoughts and findings on this little board in the coming days/weeks.

The amplifier board is powered by a single supply from 12-25VDC. Anecdotal reports on the TPA3116 claim it is happiest between 19-21VDC. I just so happened to have a half-dozen AC wall-warts that are rated at 15VAC, 15W. Rectified, that is right at 21.5VDC. Hmm. In parallel, 6 of them should be able to handle ~ 90W continuous, which is probably overkill for a garage blaster. So, with this in mind, I constructed a simple non-regulated DC power supply using a bridge rectifier and a bunch of capacitance (~20000 uF) with various snubbers and discharge resistors thrown in for good measure.

The picture above shows the completed power supply being fed by 3 of the transformers in parallel. Care must be taken to match phases on the transformers as they were wired with no regard to phase at the manufacturer. Reversing a phase on one of the transformers leads to a short circuit condition, which can quickly destroy the secondary windings. Be careful!

I'll post updates on this project as I am able.

Happy building!

~ eW

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