DAN
> >The way to listen to -just- preamp noise is to solder a 200-ohm
>>resistor across pins 2 and 3 of an xlr, and plug that in as a "dummy
>>mic." You can make valid comparisons of the noise of different
> >preamps this way, assuming a method for setting them at the same gain.
KLAS
>Hmmmm. 2 * 200 Ohms in series with a condensor from pins 2 and 3 to ground!
Assuming big enough capacitors, that network would simulate a 400-ohm
source, rising to infinity at DC, center tapped, not floating.
If the mic's output is transformer coupled, the simple 2-to-3
resistor will be a closer simulation, I think, besides being simpler
and an industry-standard way of testing. One might argue for a lower
value like 150 ohms or even 50, or a parallel capacitor-resistor to
lower the impedance at low frequencies. But I'd rather keep it
simple. Big value caps that can take 48V aren't going to fit in an
XLR shell, either.
I only have schematics of a couple of mikes; I see the Sennheiser K-6
preamp is transformer coupled. The Schoeps preamp is direct-coupled,
no coupling caps. Explains why their low-low frequency response is so
good!
I see that your network might be a better simulation of
capacitor-coupled condensor mikes, but isn't the 400-ohm impedance
too high? As a mic manufacturer, you're probably more familiar with
mic electronics than I am.
-Dan Dugan
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