The microphone setup is shown here, with, and without the casing. The circuit board has been moved a little out of its locating guides. There appears to be a simple parallel RC network across the microphone positive and ground. The capsules are set at 90° to each other and the microphone can be pointed towards a sound source whilst retaining some stereo separation.
 
CZ034GU Specifications

I designed and built this microphone specifically for the Olympus recorder shown above. I wanted to use this in place of the Olympus mic because its plastic casing causes over-emphasis at certain frequencies.

The body is constructed from nickel plated brass tubing. Small rubber lugs were added to locate with the depressions in the top of the Olympus recorder, to ensure correct alignment when plugged into the recorder. The 3.5mm plug is offset on the body to align with the position of the mic socket on the Olympus recorder.

http://www.youtube.com/wsclater?gl=GB&hl=en-GB#p/u/18/k6WFhRSbp4M

This microphone employs two 6mm diameter Panasonic WM-61A omni directional electret capsules fitted into each end of a 390mm aluminium tube. The capsules are very sensitive, and have a fairly low noise figure. To reduce resonance, the tube is packed with putty. The rubber rings on the tube help to locate foam windshields (shown right), and are beneficial when laying the microphone down. The design relies on powering from a recorder. Handling noise is acceptably low, and the microphone produce a nice quality of sound.

I needed a very small preamp which would operate from low voltage small batteries. I found nothing suitable available commercially, so I had to set about designing and building a preamp device myself. I wanted to use this in conjunction with a small digital audio recorder which had no microphone input.

I identified the TEXAS INSTRUMENTS TLV2461 and a simple preamp circuit on their data sheet. I based my design on this circuit. changing the feedback component values to provide a gain level of 35dB. This IC will operate with a supply down to 2.8V, with low current drain, and has a low noise figure.

I fabricated a case by cutting apart a plastic box and reassembling one with final dimensions about 45X15X13mm, completing it after the components were assembled. I decided not to use a circuit board, and instead position each component to make best use of the limited space available, and wire the components point to point. I had some difficulty obtaining the tiny 0.25 watt resistors, and proceeded with the larger size, giving myself some extra problems fitting and soldering the components in such a small space. The series combination of 1kohm and 4.7mF in the feedback should give some low frequency roll-off. The -6dB point is about 33Hz.. The design employs three AG12, 386 cells.

The device seems to work well, coping with a wide range of levels despite there being no adjustable gain level anywhere in the system. The unit was designed specifically to plug directly into the Ripflash Plus, but it can equally well be used in-line.

Left, a diagram, taken from the Texas Instruments data sheet, which I based my design on.

These capsules were used in this DIY design. They seem very similar to the Panasonic WM55A capsules. I used an 1/8", 3.5mm plug from some old earphones. The black base and top came from a surplus plastic box. The capsules are held lightly in place between foam plastic and the same fibrous material which fits behind the perforated metal screen.

This recorder has sensitive fairly low noise inbuilt microphones. These are not very directional, nor are they widely spaced, so stereo separation is fairly limited. On the positive side, they are not very susceptible to handling or wind. The input socket accepts a stereo microphone, and also serves as a line level input. It has 2GB of inbuilt memory - expandable with micro SD card s of up to 16GB.It records at up to 192kbps. 75 - 20KHz response. It has a small but effective front mounted speaker.

http://www.youtube.com/watch?v=B2BqinPwAKI

The AX412 case opened up to view the microphone placement. Each capsule is set into a soft rubber housing. Note that the microphones are not directional types.

Very small and light. Power: one AAA battery.

It produces high quality recordings with an external stereo microphone. The inbuilt mics are directional, and produce a good stereo separation, but they have quite a poor S/N ratio, and poor low frequency response This recorder has a 1GB memory, and records in WMA format, at up to 128kbps. Olympus quotes 50-19KHz, but this lower figure cannot relate to recordings made with the inbuilt mics. There is a very small front mounted speaker and an extendable USB plug for downloading and uploading.

"Ultra low-noise" - High sensitivity - 10mm diameter

Specifications | UK source | US source

It is recommended that the capsule is operated at or near its minimum voltage supply of 3 volts to ensure the lowest noise operation. It seems to work well using the 'plug in power' of the Olympus and the Sony recorders above. The open input voltage of the Sony is 2.2 volts. The DC voltage measured at the capsule is 0.8 volts, and 1.3 volts when the capsule is connected to both channels of the recorder. There appears to be a resistance of 100 ohms between pins 1 and three, although the data sheet does not show this. I used pins 1 and 2, leaving pin 2 untouched.
Microphone comparison test using the Sony ICD-AX412 recorder. MP3, 192bps, 44.1 KHz

Construction of mono and stereo microphone bodies for the EM172 cartridges.

I used the aluminium tubing from cheap AA battery torches (flashlights) for the bodies of the microphones. These torches cost only £1 UK each .I cut the body of the torch and smoothed down the ends.

The stereo microphone uses two torch bodies, with a capsule at each end. I joined together the caps which originally gave access to the batteries. The capsules are spaced by 32cms. The construction design allows these microphones to be easily disassembled.

I used the spring from a clip to make contact inside the tube. This ensures that the tube, and the mesh at the end are grounded.

An O ring fits around the capsule, and this assembly sits at the end of a plastic tube.The outer silver coloured mesh fits over the end this tube. The tube, capsule and mesh fit tightly into the aluminium tube.