On Wed, 03 Sep 2003 23:43:48 -0700, Bob Cain
wrote:

Go for it. Can you give it 20 dB of variable gain and about
-140 dBu EIN?

Variable gain is "built in" to any simple design, by
changing the loading. FET's are high output impedance,
current-source devices, and don't mind us loading them
with a resistor to set gain.

That's a good thing because we have the phantom
resistors, 13.62 K ohms, and the mic preamp's input
impedance to drive anyway. We'll just add another
(resistive) load in parallel.

The noise requirement of 125nV is equivalent to about
50 ohms at room temperature. Might be too strict for
300 ohm sources, but it's do-able with common FET's.
Each will need to have a transconductance of 40mA/V
because they're in series as a noise source.

I'll try to sort a batch of 2SK369's today or tomorrow,
to see what kind of matching we'd get in a random batch
of 16 from MCM. And post back.

Thanks for your interest,


Chris Hornbeck