Hi there, sorry I think i was editing my post as you where writing the reply.
Thanks very much for that explaination. I think I understand how I could not use a PNP transistor in the method that I suggested now.
However, could I use a NPN? From your explaination, I conclude that I could use a one, rectfy the amp output and curent limit, then a high signal on the base would flow through to the emitter , but 700mv less than the volatge on the base.
Is that anywhere near correct?