[Audio Empire]

On Tue, 23 Mar 2010 22:58:47 -0700, Kevin McMurtrie wrote
(in article ):

In article , Randy Yates
wrote:

Is there ever a reason NOT to use a differential amplifier as
the first stage of a microphone preamp?

Differencing doesn't have to be in the first stage. I just has to be
performed before common mode noise would be amplified too much.

In laboratory circuits, sometimes a high impedance voltage follower
buffers the input before the differential amp. The output of that
follower also drives a shield on the input wire. The result is a
virtually perfect cable with no capacitance and no insulation losses.
(It only works as long as the electrical wavelength of the input is much
longer than the wire, as with audio.)


Yep. But this technique is rare in most modern microphone preamps because
it's more expensive to implement.