Odp: [sdiy] Optimum Input Impedances

[Roman Sowa]

I recommend reading Analog Davices Application notes:
'simple' formula for calculating opamp noise (AppNote 253):
http://search1.analog.com/searchProxy.asp?redirectQuery=redirect%2Ehtml%3Furl%3D
http%3A%2F%2Fwww%2Eanalog%2Ecom%2FUploadedFiles%2FApplication%5FNotes%2F35307085
0AN253%2Epdf%26amp%3Bcthr%3Dcgrp3%3B1%3Bqt%3Dan%2D253%3Bfs%3D

"noise and operational circuits" (AppNote 358, over 30 years old, but still
good):
http://search1.analog.com/searchProxy.asp?redirectQuery=redirect%2Ehtml%3Furl%3D
http%3A%2F%2Fwww%2Eanalog%2Ecom%2FUploadedFiles%2FApplication%5FNotes%2F54801172
81535838576388017880AN358%2Epdf%26amp%3Bcthr%3Dcgrp3%3B1%3Bqt%3Dan%2D358%3Bfs%3D

some good tips can also be found in any super-low noise opamp datasheets, say
AD797

Roman

----- Original Message -----
From: Glen <mclilith at charter.net>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Tuesday, September 23, 2003 6:57 AM
Subject: [sdiy] Optimum Input Impedances


> 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
>