It's not a BLUE 47. I'm pretty sure Martins worked on it way before those, but I'll try to find out from Carlos. I would also say that, for around 3-4 years now I have been paying attention to the sound of every 47 that I come into contact with (here in L.A.) and I've only found 2 that really remind me a lot of each other; one is from a rental company and was worked on by Klaus, the other is stock and is owned by some friends who own a studio and a rental company. At some point I want to get Dave's Church mic in the same room as one of those two. FWIW, Carlos's mic reminds me more of those 2 than several other stock 47s I've used and therein lies the problem: what if it turns out that Carlos's mic is a BLUE 47, but still sounds more like one of the 2 I've used that seem quite similar than other stock 47s? If that is the case, what is the standard? How do we define the standard? Since nobody, including Klaus, seems to be able to agree on a proper, repeatable way to test microphones where more than a handful of people can share in the results--because everything is suspect, from source material to recording methodology--we are left with a situation where all we can go by is what individuals who use these things report about them; hopefully they report truthfully and with a deep enough 'rudder of experience' that their judgements have merit. But I'd be the first to admit, I still learn new things every single day.