The 1N4148 is a bit wimpy at 300 mA max FWD current. The idea is to prevent accidently trying to charge the battery. It might be OK. The resistor is to make it current limited. You usually need the 9V clip to make the connection to the battery. Heat shrink tubing would be useful.
I'll get a better diode and some heatshrink when I can.
--
Wow. Actually had the boards made, that's impressive! Literaly built from scratch. Fantastic recuperation with the NPN PNP inversion too, quite a story. And now I understand how you quickly caught on to the "thump suppression" cry for help on my end.
In all honesty, the sub is not that great; but I tend to be stubborn, and am really using this as an opportunity to learn. As challenging and frustrating as it may be at times (magic smoke!), I'm actually enjoying it, learning from it loads, and could well even consider building some (simple) electronics from scratch after this. I have a fair bit of reading and learning to do though. The basics I was taught at school are slowly coming back, but I haven't fiddled with electronics in a long time, and never to that extent.
Once again though - I really appreciate your responses, time spent and help here. Even if I do end up burning everything to oblivion, it's a good learning experience (and I won't give up unless the whole thing literaly catches fire!). I'm even surprised you carried on advising me, especially after a couple of clumsy mishaps that clearly show my incompetence!
I'll take at look at that article, it looks like fun, but rather daunting!