Kevin McMurtrie writes:
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.
Hi Kevin,
Do you mean *two* "high impedance voltage follower buffers", one for
the "+" and one for the "-" of the differential input signal?
The output of that follower also drives a shield on the input wire.
"that" follower? Which one? Are you talking about shielded, twisted
pair cable?
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.)
Without the previous clarifications, it's hard for me to grok this
last statement, but it sounds like an interesting result.
--
Randy Yates % "Though you ride on the wheels of tomorrow,
Digital Signal Labs % you still wander the fields of your
% sorrow."
http://www.digitalsignallabs.com % '21st Century Man', *Time*, ELO