Op-amp gain question -- should be easy

Paul · 2005-05-30T02:55:35+00:00

If I have a non-inverting amplifier, the gain is normally 1+Rf/R1.So if I had 9k for Rf and 1k for R1, the gain would be 10.Now how do I calculate it if I put a capacitor with an equal Xc value to R1 in series with R1????I thought I just calculate Xc, add it to R1. Then I would divide Rf by that answer. But it doesn't seem to be the case, my gain is higher. I'm using 18k for Rf, 2k for R1, 5uF for C1 and 17Hz input. At 17Hz, my gain is 7.3.Can someone shed some light on this?? I've spent a few hours on this problem and I don't know what to search for because I don't know what this type of circuit is called.thanks in advance!