Hi Brett,
I own one U47 with a K47 capsule, and am getting a second, older U47 repaired, which has a M7 capsule with it.
When I get it back from repair, I will be conducting some tests, swapping out different components in each, to compare them more accurately.
One of the tests will be pink noise, then white noise, and some sine waves at various frequencies, all at the same level and coming from the same sound source speaker, distance, etc.
Another test will be a few instruments I have, into the various combinations of the two mics, again at the same distance from the mics, and recorded at the same time each pass, to minimize chances of the instrument being at a different position. I might build a holder for the instrument, so I cannot change the position of it from the mics.
I plan to swap :
a.- The capsules between the two bodies as they are with all other components as I bought them originally.
b.- The tubes, with all other parts in their original bodies (since I have an Andreas Grossman replacement "tube" to test on the older mic,thus necessitating the tube swap).
c.- The mic to power supply cables, with all other components in their original mics.
d.- The power supplies, with all other components in their original mics.
This will give a few answers as to how the M7 capsule works, as well as the Andreas Grosse "tube" replacement, which is actually a solid state solution, which uses exactly the same voltages as the VF14m tube. If this replacement proves to suck, I will then save some money for a genuine working and tested VF14m tube, and buy it from whomever is a reputable seller (Klaus Heyne, or anyone else respected in the mic community). FYI: I don't sell tubes. K.H.
I should have this mic in my hands in a few weeks... and after the tests are done, I hope it will be useful for the general community here, to dispel a few myths, and also to create some new questions regarding mics in general, and specifically to allow for people to listen to these tests, and then do their own tests in their studios, following my methodology, especially when comparing the multitude of U47 clones now being made.
This test will live on my website indefinitely, and at 24/96Khz sample rate Broadcast Wave audio files. I'll probably include the Pro Tools session with a zipped archive for download, along with a PDF detailing the process, and a few pictures for good measure
Cheers