This is a Microphone Preamp (SSM2167) with Compression, a noise gate, and AGC. I disabled the noise gate. I was looking for a sensitive low-noise mic to do some outside recording of nature sounds and stuff. With the noise gate turned on, and as light as I can make it, I had to talk loud into it to even open the 'squelch'. The app notes call to use a maximum 5K resistor on the noise gate pin or it could cause problems. The problems manifested into loud pulses when it was quiet. There appeared to be some circuit bumping the AGC voltage to keep it over a certain voltage. During the 'bumping' the output voltage would take a negative swing. With a 1Meg resistor from +V to the AGC capacitor, these pulses disappeared. I used a potentiometer to find this value, and 1Meg is where the pulsing stopped. This worked on two chips, but it might be close to the edge. You might need a slightly smaller one, like 820K.

I built this on a piece of copper clad. The chip is glued down upside-down. This held the bugger still while I was soldering. Overall, the length of the clad is less than 1 inch. I build clad sides and a 'roof' soldering them all together in a copper box to minimize RF and other induced noise.

Total current drain with the electret element is under 3mA. With the noise gate enabled, when 'squelched' and quiet, the current actually went up an additional 1mA (only when squelched). I haven't put this on the recorder yet, but using a scope, it looks to have very low noise and high sensitivity! This might even 'hear' a fly a few feet away! This is exactly what I'm looking for.

Here is a picture of the latest box to use the SSM2167:

This has input power filtering and regulation. I've removed the compression resistor which makes a harder AGC control and a bit more gain too! This box is crammed! You may need to zoom to see the 10 pin chip at the bottom..
I've been playing with a program called PCB123. I built another board with this chip with all SMD parts/1206 resistors and caps, and I built it tight, with my own pads, but it's not as small as what I have here. I could go with 0603 parts which will match the chip, but it's tough soldering.