[sdiy] Optimum Input Impedances

[Glen]

I know there are lots of other factors involved in selecting the input
impedance of an op-amp circuit, but if you want to optimize for lowest
noise, what is the procedure? I assume it involves some calculation with
the equivalent input noise voltage and current ratings? Does anyone know a
fairly simple procedure for this?

On a different note, but somewhat related, how do you determine the amount
of loading a circuit's output "likes" to have? For example if you had a
microphone, or a Hammond tonewheel generator, or whatever, of known
impedance--how do you determine the optimum load for your signal source?
This question might be harder to answer, because I think there are so many
different possible situations that it would probably be too hard to give
any universal rule of thumb, but in case I'm wrong. let me know the
universal rule of thumb.   :)

thanks,
Glen