One area that must be got right is the system earthing. Specifically how each object is earthed with relation to each other object – by ‘object’ I mean PSU, Regulator Board, Relay Board, Left PreAmp etc.
Apart from having separate earths for left and right channels and separate earths for pre and power amps, there are several separate earth leads for the different stages within each of the power amps. Most designs do not go to the trouble of having separate leads for the different stages of the amps but I feel it is important.
The whole thing is made more complicated by having two separate power supplies; battery and mains.
I guess what I am trying to do here is to make excuses for staring at the computer screen for such a long time, without seeming to be doing anything. I think there is a decent amount of staring still to do…