Good day to all. I would like to hear some opinions regarding biasing.
In an amplifying scenario such as a tube microphone circuit there is more than one school of thought in terms of design. One of the elements of said designs is the form of biasing. While I happen to enjoy the second order harmonics, earlier breakup and "warmth" many times associated with self-biasing in my microphones, many venerable microphones of fantastic design use fixed bias (U47, U67) and some have changed over time (M49 revisions). Obviously a "good" or "great" microphone is more than just the sum of its parts (sometimes and depending upon who you ask) and the overall sonic results are dictated by the complex interactions of the entire circuit, not just the influence of one design parameter. However my inquiry will be twofold:
1) Historic: Was the choice for self or fixed (in regards to "high end" condenser tube mics...i.e. the M49's revision c switching from fixed to self) made for a particular sonic reason or was it a budgetary concern? Or both?
In my opinion, all things being equal, it must have been a total design consideration, i.e., whether or not small or large amounts of NFB was being used (if any at all), tube considerations, headroom etc. This only seems reasonable assuming the designers realized and understood it as being a whole interactive system, not separate design parameters independent of one another that theoretically "should" work in harmony. It seems to me that Neumann and A.K.G. would see it as a total design function. I am not questioning the wisdom, merely the motivation, seeing as how it does have audible results.
Or was it simply what they figured was appropriate, given the resources and knowledge of the time?
2) Design: To the designers, technicians and modifiers participating in this forum I ask this:
Why do YOU choose one biasing scheme over another? Given the wide availability of parts and manufacture and significant access to great designs of the past and hopeful self-curation of microphone advancement, it seems to me that the biasing structure would be a decision of primarily sonic considerations.
Mr.Archut: Your CS-4\
Mr.Josephson: While I cannot think of any tube microphone you currently manufacture, your knowledge and opinion is still greatly valued and desired.
Mr.Bock: Your 507
Mr.Heyne: Any particular 67 or 49 modification stand out to you in this context? Or perhaps your KHE?
While this post does have a very wide arch, I hope the answers achieve some specificity, if not then just some insight and opinions of well informed individuals, hopefully all contributing to the understanding and love of tubed microphones!
This has been an area of interest of mine since I began my wonderful trip into the wonderful world of microphones. I hope, given this forum's wealth of collective knowledge, that not only can we see into the design wisdom of the past but also into the current designing spirit.
Thank you all!