# 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. – JimmyB Jun 29 '16 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. – JimmyB Jun 29 '16 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 – Jeremy Leaf Jun 29 '16 at 15:00
• What is the purpose of C1? Why didn`t you use a parallel LC bandpass? – LvW Jun 29 '16 at 15:00
• @LvW, the signals I'm using are quite low frequency. About 20KHz. I think for that case RC filters are fine? – Jeremy Leaf Jun 29 '16 at 15:04