My sturdy NAD amplifier developed a fault where the left channel got fainter and fainter. I have the service manual and I think I know where the fault is, but I haven't got a round tuit fixing it. Meanwhile I listen to music all the time so I would miss not having an amplifier. #Playing music remotely with bluetooth was partly a response to the deprivation.

Knowing now that class D amplifiers are small, cheap and powerful, I thought I would buy another, more powerful, amplifier board and retrofit it to an old amplifier case. The amplifier you see came from some garage sale or other, I don't remember. I do remember that I bought it because it offered quadraphonic decoding. For a while in the late 70s, one could buy quadraphonic LP records that squeezed 4 channels onto the 2 channel groove of the vinyl. I had one or two such LPs and only ever heard them in stereo. But by the 2000s, multichannel digital recordings obsoleted the quadraphonic hacks. You can see the 4 power amplifier ICs in this top view of the amplifier.

I thought to put a SMPS inside the case and rewire the selector switch to choose between input sources. The amplifier board is totally disconnected and the volume pots do nothing. I only kept it because the volume pots are soldered on and removing them would leave even more holes in the front panel. (I may later take the pots off the PCB and remove the PCB, leaving the pots bolted on the case just for appearances' sake.)

Here's the class D amplifier I bought for about $20 delivered. It takes up to 36V supply, and the SMPS which I think used to feed a laptop or something, can supply 32V. It's based on the TDA7498 chip.

So after a bit of of hacksawing and rewiring, I ended up with the fugly amplifier in the first photo. Fugly because the board is mounted on top of the case. To mount it inside I would have to think of some way to move the volume pot off the board.

Meanwhile I bought a modern AV receiver (not just a stereo amplifier, but multichannel, includes tuners, and even bluetooth input) on sale in the end of year offers so that does duty these days. I'll put this fugly hack to the back of my to do queue and get on with other projects.