2 Op-Amps & Resistors

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sarah90

New Member

• Aug 31, 2011

• #1

Hi i have 2 op amps inverting, they have 2 resistors each, 10k, 40k & 100k, 100k

how would I work out the voltage gain

is it 40/10 = 4, then 100/100 = 1 4x1? and does the answer turn negative?

 

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MrAl

Well-Known Member

Most Helpful Member

• Aug 31, 2011

• #2

Hi,

Your gain calc sounds right. Since they are both inverting, the input voltage V turns into -V for the first stage, but then it inverts again so it's back to V.
Two inversion equals a non inversion

 

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sarah90

New Member

• Aug 31, 2011

• #3

**broken link removed**

thanks for you response, but its definitely not -4?

 

audioguru

Well-Known Member

Most Helpful Member

• Aug 31, 2011

• #4

sarah90 said:

**broken link removed**
thanks for you response, but its definitely not -4?

Click to expand...

The first opamp is inverting and has a gain of -4 if its signal source has a very low resistance.
The second opamp is not inverting and has a gain of 2.
So the complete circuit has a gain of -8 (it inverts).

 

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sarah90

New Member

• Aug 31, 2011

• #5

Okay I understand it fully now, thank you!