> I am trying to make an instrumentation amplifier (INA) out
> of 3x LF356 JFET opamps. And cannot use a integrated INA as
> I don't have any and samples may take a few days to reach
> me.
>
> Please see the attached gif of an INA. To make things easy:
> R1=R2 and R3/R4=R5/R6.
> But if R1 is not exactly equal to R2, can I use a trimpot as
> one of R3,R4,R5 or R6 to trim away any common mode gain?
> Which one of these four resistors should be replaced by it?

Hi Mohit,

R3 and R5 will influence the common mode, not R1 and R2.

Also, don't use a large value pot, use a small one in series with a fixed
resistor. For instance, if R3 is 10K, for R5 use a 1K pot in series with
9500 ohms. Make 9500 from 10K in parallel with 220K.

Cheers,

Bob


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