# Input impedance from RC filter to inverting and non inverting op amp

I am building a preamp for a sinusoidal current source. I have a two stage amplification process, with a bandpass RC filter in the middle. The second stage amplification is has two outputs from an inverting, and a non inverting OP-AMP. I want the output from both inverting and non-inverting amps to be as close as possible, but inverted. I also require V_out/V_in for the second amplifiers to be about 20 and -20 for the inverting and non-inverting respectively. This would normally mean $$-R7/R6 = -20$$, and $$1+ R4/R5 = 21$$

I have two questions.

Firstly, for the inverting amp, does the resistor in the bandpass RC filter (R2) affect the amplification of the inverting OP-AMP? Making the gain $$-20 = -R7/(R2+R6)$$ Would R3 have any effect too?

Secondly, for the Non inverting OP-AMP, as the input inpedance is infinite on the +ve input anyway, does R2 make any difference?

• Your bandpass looks wrong, specifically C1. Jun 29, 2016 at 14:20
• "I want the output from both inverting and non-inverting amps to be as close as possible" - You could of course let one amp do the amplification and have the other amp just invert it's output with unity gain. Jun 29, 2016 at 14:30
• @Jimmy, thanks, I'll make sure to correct that. And yes, that looks like that would work. Would there be any phase delay because of that? My signals are only about 20KHz Jun 29, 2016 at 15:00
• What is the purpose of C1? Why didn`t you use a parallel LC bandpass?
– LvW
Jun 29, 2016 at 15:00
• @LvW, the signals I'm using are quite low frequency. About 20KHz. I think for that case RC filters are fine? Jun 29, 2016 at 15:04