Hi again,
I'm also curious whether the Earthworks ZDT1024 EIN specification of -143 d=
BV can be taken is seriously. A figure of -143 dBV would correspond to -140=
.8 dBu.
However, there is also a theoretic limit for the EIN that can simply be cal=
culated from the value of the input impedance, the temperature and the band=
width.
The EIN of a preamplifier is usually measured with a termination resistor o=
f 150 ohms. However, the thermal noise produced by a 150 ohm resistor is al=
ready -136 dBu (A-weighted)! See http://www.rane.com/note148.html, table 2.=
So, how can Earthworks make a preamp that is quieter than the theoretic lim=
it??? Obviously, they did not use the standard 150 ohm termination. So, in =
my opinion the -143 dBV specification provided by Earthworks is just a misl=
eading marketing gag...
Regards,
Raimund
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