JP-11P-1 Input transformer improvement for electronically balanced input.
http://www.jensen-transformers.com/as/as069.pdf
Provides 5 to 6dB better S/N, better common mode hum and buzz rejection and inceased RFI immunity.
http://www.jensen-transformers.com/as/as063.pdf
JT-16-A Improves Performance of SSM2017 Mic Preamp IC.
http://www.jensen-transformers.com/as/as064.pdf
JT-MB-C Isolates both Mic and Line Inputs of Inexpensive Mixer.
http://www.jensen-transformers.com/as/as015.pdf
JT-MB-C Mic Input Isolation for Mackie Mixers.
http://www.jensen-transformers.com/as/as057.pdf
When a single microphone is used to capture an instrument or voice, the absolute polarity of its output doesn't really matter. But it is common to use two microphones, especially with larger instruments such as a piano or maybe a small string section.
http://www.ethanwiner.com/micpolar.html
This unit would be mounted in a small plastic or preferably metal box, with a 9V battery, level control, a male XLR connector (same as on a mic) and a switch. Current drain is low, since the circuit only uses one dual opamp. There is no need for a high quality device, and a 1458 is all that is needed.
http://sound.westhost.com/project50.htm
This device is a stereo amplifier for a high sensitivity stereo parabolic microphone. It can be used for listening to distant sounds. This unit has a stereo audio path that helps produce more realistic sounding audio. It can be used with headphones or as an audio source for a stereo tape recorder or a PC sound card.
http://www.solorb.com/elect/misc/bige/
http://www.uoguelph.ca/~antoon/circ/uspy.htm
http://www.uoguelph.ca/~antoon/circ/uspy3.htm