Actually, there are a couple of mechanisms that allow certain FET mike designs to get away without '1G' gate resistors.Matador said:Without a DC reference, you're relying on the tube to somehow establish an operating point based on what the grid and capsule float to "in the air". Bias point can drift based on the orientation of the earth, how the mike is positioned in the room.
Thanks for this ln76d.ln76d said:There's no "pop" problem - at least was not yesterday
When am making voice tests am a real barbarian!
If the exact voltage isn't important, "passive" is quieter than a Zener and you can usually get rid of at least one capacitor too.What do you think about Zener regulation of plate/polarisation voltage?
From the begining i decided to make it "passive" (why the hell people call it "passive"?) due to zener noise, but maybe i'm wrong?
http://tapeop.com/tutorials/34/david-royer/ln76d said:This is a part of controversy in this circuit and that's why i wanted to build it - out of curiosity.
If microphone work very well, even with not suitable PSU - why change that? What for?
Due to theory?
What's the difference between sela circuit and Royer circuit in case of grid connection?
For the many years Royer mod was made by many people - does anyone complain about oscilations or any inconviniences due to circuit design?
Doesn't the same Royer circuit isn't in his Mojave mike?
ricardo said:Actually, there are a couple of mechanisms that allow certain FET mike designs to get away without '1G' gate resistors.
Also the "better" tubes like ef86, 408A & 6072 preferred by the old gurus like Bernhard Weingartner of AKG, would have less grid leakage and so this would be even more unreliable.Matador said:I suppose one could rely on grid leakage current to form a phantom grid resistance. Seems like it would vary drastically from tube to tube.
ricardo said:I'm not knocking the idea. If there are commercial mikes using this system, then it must 'work'.
Just trying to understand how it works.
I know it can work with FETs but I'm not sure it is the same mechanisms in a tube mike.
Voltage readings of such a mike would be a clue.
Which tubes did you try with this?granger.frederic said:i always find that this kind of schematics are not very stable due to the "floating" grid biasing method , and very dependent to the tube's electrical characteristics...
I think the theoretical pros & cons are quite clear.granger.frederic said:true for me and for virtually all kinds of tubes ...
it's my conception, but i'm not trying to force anyone...
this schematic counts on the inter electrodes specs to avoid instability/oscillation, wich may vary from one tube to another, and also with tube usage
i also note that this schematic is not very popular in all the audio tube devices found in the world, especially in microphones
but it works , i've tried it a long ago with 5840 , it just not my cup of tea...