It's totally a thing. People build their own ribbon mikes. It seems to have started with an influx of inexpensive, Chinese-made ribbon mikes, which could be improved with better transformers, thinner foil for the ribbon, changes in internal lead dress and so on. Eventually, some of the people making mods decided the ribbon pickup itself, the "motor," was simple enough that they might as well build their own.
Modern materials and methods -- rare-earth magnets, 3-D printing, strong glues -- have made the construction process far easier than it once was and tiny, powerful magnets give good output in a small package.
Why do I care? You see, I own a couple of the most affordable of the classic ribbon microphones: the Electro-Voice V-2. Well, almost two; at some point after they'd stopped making ribbon mikes and run out of replacement parts, E-V began "repairing" them by removing the motor, hacking at the supports, and bolting in a simple dynamic microphone pickup! Fraud, you say? It was an inexpensive mic in its day; users sent in a dead mic and received back a working microphone, more rugged than the one they'd sent in. I'm sure they and E-V at the time saw it as okay.
One of my V-2s (a V-2A, with a multi-impedance output connector) is one of those "repaired" mikes. The years have not been kind to the old dynamic element and it doesn't sound all that great. I'd like to make it a ribbon mike again -- and if the kit I found this morning will fit, it looks as if I can! Otherwise, I'm in for some finicky bench work; but either way, it's possible.
8 months ago