Dirk said:
Looking at the OP37 (for example) with a noise figure of 3nV (root
Hz).
If I were using this as an audio pre-amp with a gain of 5 how does
this translate into the kind of S/N figures usually specced for amps
eg -NN dB ?
Dirk
You need to think about the impedance of the source before choosing the
op-amp, in case you have not already.
You would probably benefit from reading Douglas Self's books, in case you
don't already have them. On page 83 of "Self on Audio" he mentions that in
one particular circuit, the 5532 was measured to be quieter than an OP-27,
even though the datasheets would lead one to expect the opposite. I think
it is something to do with the bias current cancellation scheme in the
OP-27/OP-37 which introduces common-mode noise current, though that only
matters when the impedance presented to the two input pins is not equal.
Here is some stuff about op-amps and audio
http://www.dself.dsl.pipex.com/ampins/webbop/opamp.htm
Chris