I was looking at some new alpine mrp amps, they are pretty small and look hard to work on with all the SMD. They are done well and made in China, I mean no sloppy solder or anything. The M650 even has a 4 layer board in it as I recall. Unless the board is made elsewhere. I'd guess they are made by machine. I wonder about their ratings, the 450 is 400rms and the thing is really small.
That is the thing, I have an infinity here that is 111w rms x 4 @ 4ohms. That is a beast by old standards and can be bridged. They seem screwed together better than many, but I have never used/heard one. I tested it and it works, and has some power alright. I wanted to use some old amps on my high side but hey, I may end up trying this. I figure 60-75wrms/ch is my bare minimum 100 would be better and cleaner if I crank it up some. A CA240 just sold for 160, heck I can buy all kinds of used amp for that far, far over 2 x 40w. People say the difference in sound quality is little. Now the kicker I have, I don't like it. It distorts gradually and turns to static. Problem is you can't hear just when it does it. I much rather have one that breaks up in the bass like the old alpine I had in there before. That really bothers me. Oh and it is not that strong an amp for the ratings, but the sub part of the kicker works well.
I wonder if there would be an interest in a DIY old amp, or maybe even if you had the board made with the small components and a case for it. I guess I never added it up, but the parts don't seem to cost much.
Note that I don't count them, but these prices look to have all kinds of old amps up for sale now. Some I have been watching had as many since start of year as well over 6 months before that.