| Philip Soash wrote on Sat, 08 April 2006 08:38 |
Someone want to explain this Spec.
Mic EIN
Found on Pre Amp specs.
|
"Equivalent input noise." It's the noise added to an input signal by the preamp.
It should be measured with the preamp at maximum gain and a terminating resistor (between pins 2 and 3) whose value is equal to a microphone's impedance (usually 150 ohms). The resistance value is important, since resistors are noisy. A valid spec also includes the bandwidth over which the measurement was made, as well as the temperature (resistor noise varies with temperature).
The theoretical minimum EIN for a 150-ohm source impedance over a bandwidth of 20 kHz at room temperature, no weighting is -131 dBu. (This number is a VOLTAGE, where 0 dBu = 0.775 volts.) This theoretical number implies that the preamp itself is noiseless. There are conversion functions that let you represent this number in terms of Noise Figure and nV/sqrt(Hz) but I don't recall them offhand.
EIN is probably one of those specs that you don't need to worry too much about, as it seems like everyone's preamps do -129 dBu EIN without too much trouble.
-a
