Calculate Op Amp Gain

[Harald Kapp]

How can you say that R1 has "no influence"?

"No influence" as long as the opamp's gain and drive capability are good enough to compensate the effect of R1. Gain is from Vout to Vin and therefore any voltage drop across R1 is compensated by the (ideal) opamp.
As I stated, in "reality" (if you accept the simulation result for such), there is a dependence on R1 and frequency due to parasitics.

No, the gain is 1+R2/R3 . See post #11

I fear a misinterpretation on your side or maybe a not so good expression on my side. Whatever: The gain is 2 = 1+R2/R3, not 2*(1+R2/R3, as my expression could be misunderstood. Sorry for not being totally clear.

 

[LvW]

Duke37, Harald and Ratch - yes you are right.
Indeed, R1 cancels out - independent on the respective values.
I am getting older and older...

 

[BobK]

The confusion is about whether we are talking about the gain of the opamp as being the gain from the input to the output pin of the opamp, or the gain of the entire circuit, which is from the input pin to the junction of R2 and R3. The two are obviously different.

Bon

 

[Harald Kapp]

I am getting older and older...

We all do.

 

[duke37]

[QUOTE="LvW, post: 1735547,
I am getting older and older...[/QUOTE]
You will need to run fast to catch me up

 

[LvW]

[QUOTE="LvW, post: 1735547,
I am getting older and older...

You will need to run fast to catch me up[/QUOTE]

Are you sure? (I am 76.5)

 

[duke37]

You will need to run fast to catch me up

Are you sure? (I am 76.5)[/QUOTE]

I have just passed 80 and seem to be travelling faster and faster. The 37 in duke37 is my date of birth.
I will have to decide what I should do when I grow up.

I am training to be a 'silly old fool'

Trevor

 

[LvW]

OK - you win.
Congratulation.