Some years ago I was quite active in soldering sound stuff. At some point I didn't have the necessary time any more so lots of things got forgotten. Now I found one of those little thingys and went through the process of reverse engineering to understand what I did. The pream presented on this page not equipped to be used with el-cheapo pre-polarized condenser capsules (those el-cheapo elektret thingys); it's intended to be used with dynamic or ribbon microphones.

One of the things I had build back then was a preamp for dynamic microphones. The nice thing about this preamp was that it was phantom powered and pretty small -- essentially 2 transistors. I built it at some point, not on a board or anything, just on the fly, hooked it up to two XLR connectors and tested it. Yep, worked pretty well, the noise added is reasonable in relation wo the amplification this thing gave me.
Then I put it to the rest of the experimental sound stuff and forgot about it. For years. For 2 moves. Recently I rediscovered it, tested it and noticed that I have no documentation whatsoever. So this was my starting point:

And then I went on, got me the mangnifying glass and worked my way through the resistors -- thankfully both capacitors and transistors are labelled in a somewhat readable way. I ended up with the following:
Part list:
2 Electrolytic capacitors 100μF, 25V
2 Transistors BC549C
2 Resistors 22Ω
1 Resistor 300Ω
1 Resistor 470Ω
2 Resistors 27kΩ
2 Resistors 220kΩ
Considing that being less than 5 bucks (not counting the XLR connectors) -- that seems a good deal to me.

Disclaimer: I do not recall how it came to that circuit. I might have seen it somewhere on the Internet and tried it out for good.

Update 20180506

More than likely this is the "Ribbon Booster" as presnted by Panik Pro -- http://panik-studio.de/diy/files/ribbonbooster/schematic.jpg. Unfortunately the site is defunct (or "Under Construction" as it declares in a wounderful 90s style) so literally the only thing that seems to work is directly accessing files.
Just to prevent the file from disappearing from the net, this is a copy. I do not claim any rights.

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