Here's the spec sheet on the mic capsule
http://www.panasonic.com/industrial/components/pdf/em07_wm60_a_dne.pdf
Here's some more info I found on someone else experimenting with this capsule:
"A high quality measurement and recording microphone with flat frequency response can be constructed using the Panasonic omni-directional back electret microphone cartridge WM-60AY. Currently it is priced at $23.41 for 10 units(!) under Digi-Key part number P9959-ND.
When the cartridge is connected as described by Panasonic it produces fairly high distortion at moderate SPL's and is marginally suitable for serious recording and measurement purposes. The microphone itself is extremely linear, but the built in FET amplifier stage is not configured optimally.
Fortunately, is it possible to modify the external connection to the FET. This involves some delicate work of cutting a trace on the tiny pcb in back of the cartridge and soldering thin, flexible wires to the standard two hookup points, and making a different connection to the capsule housing. The pcb has a circular ring of copper on its outside, which can be exposed by shaving off a small section of the aluminum roll surround with a sharp blade. Then solder a wire from the copper ring to the hookup point that was originally the positive capsule terminal and make it the new ground wire. The terminal with the cut trace becomes the new active output. You might sacrifice some cartridges while learning the process. It is important not to overheat the cartridge when soldering the wires to it, because it destroys the electret. Also, after wires have been connected, the whole backside should be covered with Silicone II Glue to avoid low frequency roll-off due to a broken air seal which might have been caused by the modification. Heat shrink tubing can be used to attach the capsule to a wooden dowel, or the capsules can be glued into the end of a 1/4 inch ID thin metal pipe. Look at the microph1.gif page from my notebook for further details.
The output voltage from the modified WM-60AY capsule can swing 5 Vpp (!) max at 141 dB SPL using a 9 V supply, and easily overload a preamplifier with too much gain. Noise floor measures about 36 dB SPL, 80 Hz to 20 kHz, with a 1/f corner around 100 Hz. A-weighted noise is estimated as 30 dB(A).
A more sensitive capsule with a few dB lower noise of 26 dB(A) is the WM-61A. It outputs a maximum 5 Vpp at about 134 dB SPL.
I first learned about the microphone modification from Lyman Miller, Palo Alto, a friend and former colleague at HP, who does some of the most natural sounding recording I have heard.
The wiring diagram for a stereo microphone with output attenuator, if needed, and using the modified capsules is shown on the microph2.gif page. Attenuation of the microphone output degrades the signal to noise ratio and should only be used, when the preamplifier gain can not be reduced.
A discussion of microphone issues can be found at the MicDIYers forum."
This came from
http://www.linkwitzlab.com/sys_test.htm if anyone wants to read more. Also there are some pictures and schematics there.
DD
I am a total clums with electronics..