Got some time Thursday and today, and finally got a lot of my thoughts down as actual schematics with parts values (!). Four pages and counting. I've also tentatively laid out which functions go where on the new physical layout, so I can draw the actual wire bundles. Once that's done, I can start doing the detailed PC boards. (Don't worry, all the signal voltages are off the boards - it's just power supplies and sequencing logic.)
One of the things going into this design is an RFI filter at the power input; I'm following Buddha (the late John Camille) in using a commercial RFI filter followed by a homebrew lower-frequency filter that gets down to 2kHz. I've gone back and forth on how to do this, and how complex to let it get, but that's where I am now.
The power and protection sequencing was a bear since I didn't want to use digital counters. At this point there are four LV regulators and three relays in each amp. I had worked it out a month or two ago, but getting the details down on paper (and fixing my hand-waving!) was a chore.
