[Laser] discrete vs op amp sensitivity

[F1AVYopto at aol.com]

Art

>I'm not sure I agree with  this,  although I do see your point.
>But, let's look at a fictitious  example........
>Let's say you and I use the same optical detector and we  are 
>attempting to detect the same weak signal.
>Your sound card  has 6 db more noise than mine does (with the inputs 
>shorted and looking  at relative output).
>I think my SYSTEM would hear (detect) a signal that  was 6 db weaker 
>than your system would hear. Correct or not?
>I  wouldn't argue that the preamp gain is much more significant as a 
>noise  source, but to treat the final output stage as though it didn't 
>matter  much is not correct either.

I imagine two sound card.
One has an  intrinsic noise 6 dB above from the other.
If we use a FFTDSP program with a  very small signal, I can adjust the input 
signal so that it will be not detected  by one of the card at the same 
parameters....
This signal will be very small  and a sound card must always work at a strong 
input level!
If now I use a  good low noise preamplifier in my photodetector to boost my 
input signal 30 dB  above the audio cards noise, the cards noise effect becomes 
fully  negligible.
The Input level could be a very strong noise with a very small  useful signal 
hidden inside but the FFTDSP is made to extract it via its  spectrum.
The card noise adds itself as a negligible part in the total input  signal if 
its level is sufficient.
73, and thanks for the comments.
Yves  F1AVY