Marik said:Bob,
Are you talking about conventional connection? Then yes, it is self biased, and is done through gate to source forward current, which is very small. However, I am using it as 'cathode follower', and believe that source resistor (which is BTW another source of the noise--I am using here Vishay 0.1%) sets the current--
Hmmm.. all this talk of Johnson noise makes me wonder.. always thought that was the name for electrons banging around against moving atoms in the current flow, since we aren't dunking the whole thing in liquid Helium.. and the air motion noise would be called something else? ( Browninan noise?)
Anyway.. since the resistor is fairly large (10K) finding a low noise type might be an improvement.. wondering if anybody's done some experiments in usng a smaller one that would reduce noise contribution? (but probably also reduces the gain/sensitivity)
Don't know how much lower you could go, and then amp it back up downstream with the off mic preamp, before you lose whatever you gained in extra preamp noise, but it might be an approach to try, as well..
Damn.. I keep talking like this and I'll have to buy a ECM8000 and some WM61's, too!! ;-)
BTW, did a bit of research on phantom power balanced mic connections.. I see now why you have current restrictions with the fairly high value pair of resistors in series with the power.. and thereby why you can't easily draw more than a little current.
Wonder what the voltage is at the FET pair after the drop.. If it's close to 10v, perhaps putting the regulator upstream so it powers everything, and thereby has more current flowing thru it, or even having a reg for the FET's and the mic for two different voltages.. but there I go with more parts to squeeze in.. ;-)
Jon