I am working on my own version of the Squelette mini chip amp, as presented in Make Magazine #23. My ambitions for this project are relatively unbounded, but knowing the trouble I have with follow-through, I am trying to start small and get a working stereo amp with a single input and potentiometer volume control in an enclosure, and I can leave the integrated WiFi radio, IR remote control interface, smart phone remote control interface, integrated digital tone and volume controls, blinkenlights, and mind-control interface projects for later on.
What could I call it, but the “Schamplifier”?
Anyway, the circuit is pretty-much the same as the one presented in Make, but I decided to design my own PCB for it. I took inspiration from a number of other LM1875 PCB layouts described on various DIY audio forums. Each channel has its own (identical) board, and they are all interconnected with wires and terminals (so I can experiment with other modules later on, e.g., tone controls).
Here’s the schematic, layout, and finished board for one of the amplifier channels:
This is pretty much the schematic from the Make article.
Note the star ground point, and the super wide power and signal traces.
Another fabulous result of my toner-transfer silk screen process…
The etched boards, with my attempt at tinning the traces. I consider this to be “mixed results”, we’ll see how it sounds. I’m considering having some PCBs professionally fabbed, more on that later.
Here’s the schematic, layout, and finished board for the power supply:
I’m thinking of re-swizzling the board a little bit, and ordering a few professionally fabbed (all the more if there are noise issue because of my crummy home-made PCB). If you are interested in getting in on the group order, let me know, they would run about $5 each, shipped (remember, you probably want two of them…).
Current source files for the boards are available on my GitHub repository.
Before I can really test the circuit out, I need to get an adequate heat sink, and since my heatsink is ultimately going to be the enclosure, I’m trying to finish the design for that before going on. This is not too difficult, but finding the right information proved a bit tricky, so I’ll be covering heatsink design in its own post real soon now.