Audioguru, I have another question...
I've been testing a couple of different electret mics with just the preamp part of your circuit - so I have disconnected the link from C4 to R9, and I take the output after C4 and run it through my scope. I am seeing quiescent voltage at 0V, with a range of -2.2V to +1.5V, but I see clipping at the ranges (so at -2.2V and +1.5V) for loud sounds. If I take the preamp out of the picture and just take the output after C1 to the scope, I see much lower voltage of course, but I can't see any clipping. Unless I'm just not seeing it because of the scale on the scope, it looks to me that the mic is not clipping and that the preamp is. Is that likely, or is it more likely the mic and I'm just not seeing it? If it is possibly the preamp, can you suggest how to stop the clipping?
Actually, I have another question - just to satisfy my curiosity. As I mentioned earlier, my background is software, and I dabble in hardware - I (try to) build robots. In the scenario above (preamp only, no peak detector), I noticed that if I take the output before C4, the scope shows quiescent voltage at 2.3V (vs 0V if I take the output after C4), and the clipping happens at a few mV above 0V and at about 3.75V. Why is that? I don't understand what taking C4 out is doing in that circumstance.