Dear Davids (Satz, and Bock)
Thanks for chiming in with your thoughtful responses. This quality of posting will be used in distant futures as reference material.
No problem disagreeing with my opinion. I love it!
But now we have to reconcile the following differences:
1. Davis Satz:
There is zero difference in the amp layout, including eq section, and capsule complement, between original 269 (non-c) and U67.
That would leave the tube. It is probable that an AC 701 (M269 mic) has a different gain than a EF86 (U67 mic)
But a 2dB variation in lows and highs between different, super high premium quality audio tube types??? Never heard of such. So, where would that deviation come from?
I listened to quite a few of of both mics in my life and cannot confirm the measurement differences aurally.
2. Davis Bock:
Of course, the tube's biasing (the way the tube is primed to perform its operation has a bearing on the timbre and frequency response of the audio circuit the tube serves)
influences the audio considerably. I thought I made that clear in my post.
Therefore the 'c' version of M49, M269, SMx and KM5x mics will always display a different timbre from the earlier non-c versions.
However, I warn the readers not to infer from this statement that later 'c' versions of Neumann (or other manufactures using cathode self biasing) is automatically preferable. Try installing the 'c' version in a U67 mic, or a U47 mic, and you will find a black hole where there was beauty before.
Let's never forget how we react emotionally to a mic: The midrange texture of the earlier biasing is hard to beat, even as self biasing lowers the noise floor and makes the picture more transparent, something is given up.
Kind regards,