I'm slowly figuring out the PMD660. It's one of those things that requires that you read the manual to get it to work correctly, and the manual is just oblique enough to be frustratingly incoherent. What I mean is; it takes about three readings to figure out the more complicated functions.
But I'm getting there.
I actually managed to do something (I'm not sure what) and lock it up such that power-off didn't even work, and I had to unplug it to get it reset. Later on I figured out that maybe I hit the Key Lock function.
It has two internal mics, and out-of-the-box it uses these, so I played around with that first. Tonight I played with an AKG 3000, which is a pretty good condenser mic. Since I normally record with a $10 microphone plugged into a computer, this was a bit of a step-up. I had headphones on, and I put the 660 into pause record, and immediately I can hear this whistling noise, and I can't figure out what it is.
It's rhythmic though...
And then it hit me: It was me..I could hear the air going in and out of my nose!