[quote author="jhaible"][quote author="Marik"]I am with Jacob and Gus about 12AX7 use for mics. Also, I could add that this tube has a very high Miller effect, so working with such capacitive source as a microphone capsule it will have severe top roll off.
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I won't argue for or against a 12AX7, but I have a general question:
Wouldn't a capacitive source and the capacitive feedback from the Miller effect fit together nicely? Source impedance decreasing with frequency, feedback impedance decreasing with frequency.
(I was surprised when I first saw a tube design that did this on purpose. In the Hammond B3 there's a mixer stage where the normal signal, the vibrato scanner signal, and the percussion signal are added. The vibrato scanner is capacitive by nature. What they did, is this: Using a feedback capacitor (instead of a resistor) from plate to grid. Then feeding all the sources to the grid via capacitors. Ok, this was no wideband circuit, of course. But if it's possible to use external capacitive feedback in order to adapt capacitive sources, it should also be easy to deal with the internal Miller capacitor of a tube, _especially_ when your signal source is capacitive. Don't know if this is relevant to the microphon thread, but I thought I'd just throw this in for discussion.)
JH.[/quote]
J.H.,
IMHO, the microphone design is much more refined than the organ vibrato, which is essentially nonlinear. I just don't really see a good reason and benefits of feedback use in mics to overcome some problems, when more suitable tube could be used, first place. It is like conciously to create a problem and then desparately try to resolve it.