Sorry Lads, really dumb opamp question

[WeAreAs1 at aol.com]

In a message dated 1/10/01 1:46:54 AM, macbeth2600 at yahoo.co.uk writes:

<< Apologies in advance! For a while now, if I want a non

inverting buffer, I take a dual opamp wire a 10k input

resistor to the neg. input, take another 10k, connect

one end to the neg. input then connect the other end

to the output, this output I then connect this to

another 10k input resistor to the other opamp which

has a 10k feedback resistor. The output of this is a

non inverting buffer amp.

The question is, would this function happen if I made

a resistor free non inverting buffer out of one opamp?

anyone know? regards, Ken >>

Hey Ken, there are no dumb opamp questions, only dumb opamps.

You have described two unity-gain inverting amps in series, which should 
pretty much act as a non-inverting buffer.  You could simply wire a single 
opamp as a non-inverting buffer and get essentially the same result.   (put 
your signal into the positive input; feed the output back into the negative 
input; with no resistors at either the input or in the feedback loop)  

Actually, the two-inverting-stages-in-series arrangement is susceptible to 
gain errors if any of the 10K resistors do not exactly match, so the single 
non-inverting stage is probably a more accurate and transparent buffer.  The 
non-inverting buffer's input impedance will be determined by what type of 
opamp you choose (bifet types such as TLO-xx will have very high input 
impedance, and will place very little load on the preceding stage).

Michael Bacich