[sdiy] Newbie alert: opamp resistor values

[Ian Fritz]

At 10:34 AM 1/8/2009, David G. Dixon wrote:
>What are the basic guidelines for selecting absolute resistor values for
>opamp circuits?  For example, say one needs a unity-gain inverter or summer,
>and is using a generic FET-input opamp (TL07x, say).  What determines
>whether one uses 10k, 100k, or 1M for the two resistors, or something
>inbetween?  Now, what if input impedance is not an issue (i.e., the incoming
>voltage is well buffered)?

Generally not too critical.   100k is standard modular input impedance, so 
that often determines the two values.  Otherwise, too large an impedance 
gives noise/offset issues, too small draws more power than necessary.  I 
say anything 33k - 330k is fine, but I'm sure you'll get other opinions.

Another consideration is to think about other folks building your 
circuit.  It's convenient to have as small a number of values as is 
practical.  So don't use 33k one place and 47k another if they could be the 
same.

Ian