[sdiy] Using Opamps as INV or NON-INV amplifiers

[Ian Fritz]

At 12:17 PM 6/21/2006, Seb Francis wrote:
>If you want to sum multiple signals together you need to use inverting 
>configuration.


As a general statement, that simply isn't true.  If you have several inputs 
with variable source impedance, then the inverting summer prevents the 
various inputs from interacting.  So in that case the inverting summer is 
adventageous.  But if you are summing signals from fixed-impedance sources, 
or if the variable impedance is just a trimmer that is set once, then you 
can use the generalized differential summer.  This saves an opamp, at the 
cost of some calculations.

   Ian