Question about OpAmps...

[Raav]

http://www.reddit.com/r/AskElectronics/comments/23i5xs/real_quick_question_about_opamps_setup_as/

(Please note: my level is novice)

Posted there, but in essence my question kinda boils down...it was stated in #600 Fundamental Fridays on OpAmps that the feedback resistor always has a higher resistance value than the r1 resistor going to ground.

I was playing with the equation for non-inverting amplifiers and again it is Av(gain)= R(feedback)/R(to:ground) +1

But I was trying to figure out how to get a ratio of 2:1 and the only way I can tell how to do that is by using the same resistor value.
Av=(1000ohms/1000ohms)+1
-or- 1+1=2

So my question is, can the negative feedback resistor be the same value or even lower (to get maybe 1.5:1?)

[wiss]

Sure! Zero for unit gain.

[c4757p]

Damn, wiss beat me to it!

Yeah, "always" is a bit silly. You shouldn't usually go below unity gain (Av = 1) - some op amps aren't stable - but there's no reason you can't go to unity gain, or below it on a decent op amp (only possible in the inverting configuration).

[wiss]

A unit-gain stable opamp (most of them) will be stable with output tied to -in, gain 1 in non-inverting conf and gain 0 in inverting. You should not put another amplifiet in the loop! Unless you know what you are doing...

[Simon]

err yes for non inverting same value resistors gives 2 gain and no problem with that.

[Fank1]

For a gain of 1 you don't need any resistors.
Just hook the output back to the inverting input.

[Raav]

Ok excellent, thank you for the replies. I thought Davey said something about feedback always being higher than ground resistor but maybe he said that in a certain context.

Thanks again for the replies.

Funny enough I was talking to my Step Father In Law (quite a title) but he is a friggin electronics genius, and I told him I was working out OpAmps math and theory and he gave me an old oscilloscope so I am going to try to rustle up a 741 or something with an OpAmp in it and actually put in a few different sets of resistors just to see what it is doing IRL