The transformer in a ribbon microphone must be designed and built to be efficient, sound good, have low noise pickup, and produce a healthy output voltage. And it must be matched to the mechanical, electrical and acoustic properties of the ribbon mic.
These qualities sometimes fight each other. For instance, if the transformer is to have high output, then it probably needs to have a high turns ratio, but that can raise the noise floor.
People have asked us to sell these to them separately, but we would have to charge about $250- to $300 each to make it worthwhile, and they wouldn't necessarily be right as a retrofit for any other ribbon microphone. Mixing and swapping out ribbon mic transformers is interesting and many people do it. As far as we know, our ribbon mic transformer is unique among ribbon mics since it isn't a traditional audio transformer design.