hank alrich wrote:
Mike Rivers wrote:
On 1/21/2015 12:05 PM, Scott Dorsey wrote:
That adds a shunt resistor in parallel with the input. So the
microphone sees a lower impedance load, but the noise is not decreased
(and is actually slightly increased).
The only way to get a real adjustable input Z that maintains noise
performance
I've only found one microphone, a CAD ribbon, that sounded better with a
low impedance load than it did with a conventional 1.5-2.5k ohm mic
preamp input. I think it's a gimmick, but if it makes a too-bright mic
sound less bright, I suppose it's good for those who have that problem
(or that mic).
The thing is that overall, adding 20 dB of output level to the preamp
input when you need it while increasing the preamp noise by only a few
dB, is better for most everyone. The only reason to fuss with that is if
you insist on only using the best designs (or nothing).
Look at the input impedance of the Gordon preamp. Never heard one that
sounded that good, more there there than I'd ever realized before.
http://gordonaudio.com/specs.htm
The specs don't tell you the full story, though. The input impedance of the
Gordon is pretty resistive and does not change at all with level. I don't
think that's a big secret to the transparent sound but it's certainly a
contributor.
That said, if you're using Schoeps mikes or something else with a super low
effective output impedance, it doesn't matter much at all. The low output
impedance of the mike means variations in input impedance on the preamp are
less of an issue.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."