http://taperssection.com/index.php?topic=90060.0This is how Mike Grace describes the differences between the V2 and V3.
"I guess the word "identical" may be a bit strong here. When we first
started development of the V3 the mic preamp circuit was "identical"
to the V2 with one exception: Most of the components in the V3 are
surface mount rather than through hole. This was necessary to
accommodate the additional converter circuitry. Components that are
not changed to surface mount include the gain control switch,
metalized film coupling capacitors, conductive plastic trim
potentiometers, HPF filter switches and XLR connectors.
As we began evaluating prototypes it became clear that the V2 style
trim control would not work in the V3 for practical reasons. (with
the trim attenuator one could be clipping the preamplifier badly and
it would not be visible on the meters) However, when the trim on
the V3 is set to 0 the circuit "topology" of the V3 is identical to
the V2 with it's trim set to 0. ....so... If you looked at a
schematic representation of the both preamplifiers with their
respective trim controls set at 0 the two circuits would be
identical. (with the possible exception of the INA163, which shares
the same architecture as the INA103 but may have subtle differences
in its internal circuit topology. Burr-Brown does not publish
detailed schematics of these devices.)
It is instructive that Doug has heard a distinct difference
between the V2 and V3 because it points out how important the very
small details in circuit design can be. How can two preamplifiers
that have the same circuitry sound different? Here are a few
possible factors that I can think of:
Surface mount resistors have no leads. They are soldered directly to
the pcb. Through hole resistor leads have inductance and stray
capacitance which surface mount parts don't have.
Use of surface mount parts permits a "tighter" pcb layout with
shorter traces. Again, less inductance and stray capacitance.
This translates to better transient response and a better ability for
the circuit to resolve complex harmonic structures and high
frequency wave forms.
Use of surface mount devices also lets us use a more contiguous ultra
low inductance ground plane on the bottom side of the pcb.
The circuit ground is THE foundation of any audio circuit and the
more solid it is the more performance potential the circuit will
have, especially in the upper registers.
I guess I have billed the V3's preamp as "identical" to the V2 for a
couple of reasons. One is to try to explain that we did not
compromise the preamplifier circuitry so that we could add an AD
converter in the same box. The other is that I did not want all of
our V2 customers to think that they were sitting on obsolete
equipment when, IMHO, it is still a state of the art preamplifier.
As a manufacturer it is very tricky to introduce a product that
replaces an existing one. Especially if you don't necessarily want
to participate in a "throw away" society where "out with the old and
in with the new" is what sustains our economy.
Sorry if this is a jumbled bunch of rambling.
-Michael"