Originally Posted by mnarwold
Thanks for the response! So, to make sure I'm understanding, this design is better able to control the power quality by doing the AC/DC conversion internally rather than relying on the wall wart for conversion? Seems to make sense, so it is a step between a totally internal power supply that requires no wall wart, and a totally external supply that is totally reliant on the wart.
So what would happen if you plugged in a DC power supply? Would it try to convert it and cause problems, or would it be just fine? I actually know the answer to the second question, since the site says it won't work with DC input, I'm more looking for the "Why".
Maybe I made too much of a distinction between where the parts are placed, which is mostly about size, weight, and cost (also handling usage at ~230V parts of the world as opposed to ~115V). The main feature we're looking at is where to put the transformer, which does the AC/AC step-down, which requires a couple of copper windings. If you use a switched-mode power supply, complexity is higher, noise can be higher, but you can use a much smaller transformer, which saves on transformer cost / size / weight. The purists really don't like that though, and it's not necessary.
If you gave the amp a DC voltage of a high enough level—maybe 15V or so?—it will just power the positive +12V fine, but you're not going to get anything for the negative rail. A lower voltage, and the positive rail should work but at a lower voltage I think? I'd need to check what those regulators do again, when operating under the dropout (i.e. out of spec and normal design operation). Anyway, the lack of the negative rail is why it won't work.
As for why, the schematic is here (<- click). The power supply is at the top. Were you looking for discussion of the electronics, part-by-part?
Edited by mikeaj - 12/28/12 at 12:17pm