I realize this is an old post, but I'm wondering if anyone has more recent experience with a DIY mic and preamp using the Panasonic WM61 electret condenser mic, and any tips on how to use with REW. I thought it might be a fun little electronics project, and I found this page also has preamp designs, though I'm not sure which is simplest most appropriate...
http://www.johncon.com/john/wm61a/
I already have a usable external USB sound card with Line In and Line Out (Diamond xs71U,
http://tinyurl.com/a7eufjc , tested and gave a nice curve with REW), so would like to make both a mic and preamp circuit with 3.5mm jack, using one of the above designs or perhaps this one...
http://www.madaboutsound.com/prod_det.asp?cid=112&sa=cf&ctid=4
I notice this site also has a calibration file, though I'm not sure if it's REW-compatible (file type is ".frd").
Looking for any DIY guidance/suggestions/tips, even if it's to say it's not a good idea & why. I like saving money and enjoy spending the time to build something if there is a reasonable chance of success, particularly since my interest is more for curiosity and learning, though I realize I might end up with something I could actually use for tweaking my sound system.

onder:
Thanks