i have an old PMD660 in a drawer but it has not been too useful to me. The preamps are not particularly quiet and don’t give much headroom, making dynamic mics difficult to use. I had other recorders (including a slighlty less hissy but “3h-on-8-AA-batteries”(!) PMD690) at that time so i did not bother with it. I read someone did a preamp mod for the 660 which apparently made it a good machine.