Stereo mic to iPhone 5S (jack) for recording I'm looking for the cheapest way to get a stereo mic signal into iPhone 5S

A google search shows a lot of expensive mic solutions using the lighting port

And some say it can't be done without some special circuit

Is it not possible to use an oldschool analogue stereo jack mic somehow?

To record the sound, in stereo, using my own stereo mic with mini-jack

Perhaps with a converter to fit iphone multi-jack standard?
You need something to work with XLR mic's such as TASCAM’s iXZ. Search for "xlr iPhone microphone" to find other's that might fit your needs better.