[ProAudio] Microphones question

[Scott Dorsey]

The answer is partly that microphones vary all over the place in their
output impedance.  Effective output impedance of some condenser microphones
is around 50 ohms.  But an RCA ribbon wants to see 2K or higher or you'll
lose high frequencies because the high frequency impedance is higher than 
the impedance at 1kc.

So... 150 ohms seems like a nice reasonable middle ground that more or less
represents a wide range of microphones.  If I was going to pick a value for
a standard to measure noise at, I'd pick something in that range.

And yes, there are cases where preamp A is quieter with the Schoeps and
noisier with the RCA compared with preamp B.  

It is stuff like this which drives the Neumann Solution-D and other attempts
to digitize signals at the mike and eliminate the whole mike/preamp interface.
--scott