D10 Bluetooth-compatible 5.0 Subwoofer Digital Power Amplifier Board mod

Title as per the ebay ads ;-)

Useful mains/DC powered board - bluetooth, mp3 from USB, line in and 2x mic in with echo ;-) The amp chip is unlaballed, but seems to be some kimnd of class D amp. The internal mains PSU provides around 19v; the DC input suggests 12-24v. (worth noting that the small version of this board, labelled 'Hifi Bass Bluetooth Amplifier Board Mini 12V 240V Stereo Subwoofer With BT' AMP-5M-C, uses half of a standard car radio stereo amp chip and only manages about 7W; this seems to have a bit more poke) The Bluetooth is the main problem though - a loud audible message on power up saying 'bluetooth mode' unless the volume is right down, and of course if connected to a phone as a portable speaker, then if in use as an instrument amp and you get a messag on your phone... I wanted to still use the board as an mp3 player, built into a speaker, but also as a small bass amp. My small rubber string bass has a preamp anyway, so just needs to go straight into to amp module. The unit has two boards - power supply & amp, and the music generation board. I was able to identify the cable carrying analogue audio between the two - the centre connection of the five pin connector on the music board (CN2 by the USB socket). Although only four pins are used, it's a useful way of identifying the cable.

I cut this wire, and extended both halves.

I isolated the first mic input socket (leaving the second one connected) and used it as a break/insert jack; leaving the board connected when unplugged, but when connected disconnects the music board output and replaces it with whatever's on the jack lead.

I disconnected the resistor that mixes the two socket outputs together, and then cut the PCB copper to isolate the normally closed contact on the socket (switches to earth when no mic connected). The music board output was connected to that, and the feed to the amp board connected to the tip connection. I then reassembled the unit and tested it. Before fitting the two mic sockest though, I put read tape over the hole for the new input jack and cut the hole through, to make it clear it is the new 'break' jack.