Prototype IV: Dead :(
Well... friend of the project Neil Davis has pointed out some flaws in the design of Prototype IV that require the entire schematic to be 're-jiggered' (see this thread over at diyAudio). The crux of the argument is that the amplifier should not be on same board as the logic board. Beside some electrical problems, from a product standpoint it ties the amplifier design to the logic design a little too closely. And there appears to be no good reason for it.
Neil's argument (something Jon has been pointing out as well) is the amplifier and the power supply should be plugin modules to the system. By pairing the power supply and the amplifier on a single board, DigiSpeaker can be designed with upgradeable paths for both logic and amplifier. This would lead to a lot product variants because each could be upgraded on their own path. Powerline modem is not working for you? Then get the logic board with integrated WiFi. Is the amplifier too low power for you? If so, then buy the next version up that has more power. And so on...
With this new insight, Jon and I have decided to split the design into two modules. They are power supply/amplifier and logic. Since the schematic and layout for Prototype IV is just one big blob, I have decided to stop work on Prototype IV and declare a new prototype. Prototype V will have much of the same work. It is just that it will come in two modules (two schematics and two layouts) that more closely follow the new modular approach.
And of course... there are a couple of changes in the works. When the power supply was separated from the amplifier, I had decided to concentrate on the logic/amp board and work on the power supply second. Now that the amp and the power supply are integrated, it doesn't make sense to just work on the Amp. In other words, the Prototype IV schematics will be broken apart and a power supply design will be added to the Amplifier design.
There are other changes coming to Prototype V like integrated temperature sensors and room correction processing. However, I will leave that discussion for when I post the Prototype V system design.