--- In Dan Dugan <> wrote:
> Adam, you wrote,
> >This brings up another complication of getting hard data that
> >translates to real field usage -- the actual source impedance of
the
> >microphone may vary with frequency from the nominal 150 ohm spec,
so
> >measurement of the source impedance of some popular microphones
and
> >the EIN of mic preamps over a range of impedances and frequency
> >would be in order. Anyone have some mic test heads for various
> >models (I have one for the Schoepps)?
>
> I used an oscillator and a pad to set a standard gain, and a 150-
ohm
> dummy input load to measure the no-mike noise (same as
manufacturers
> use for 200-ohm mikes). A low-output dynamic mike at the end of a
> 100-ft cable out on the hillside provided a real-world noise
> comparison.
Additionally to the dummy resistor of 150 ohm, two additional
resistors of about 33 kohm that simulate the phantom feeding current
of condenser microphones might be useful. One resistor should be
connected between pin 1 and 2 and the other one between pin 1 and 3
of the XLR connector (and 150 ohm between pin 2 and 3). Such an
arrangement would reveal any additional noise caused by the phantom
feeding circuitry of the pre-amp. 33 kohm resistors would simulate a
current of 2.5 mA, which is slightly more than the MKH series
microphones draw.
Raimund
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