I'm sending in a sine wave with an A = 120mVpp, f = 200 Hz into a summing amplifier, in addition to a 3.0V DC offset going into the same node, with equal weights for the resistors. I'm doing this to add the sine wave and the offset together, into one signal, so I ultimately have a sine wave with an offset. I'm sending the summing amplifier's output to an inverting amplifier to invert the signals into the positive range. After some circuitry to work with the signal after I've applied the sine wave + offset, at the end I want to remove the DC offset to interface it to a DSP chip. I can't really get into specifics, since it's for my employer, but as of right now I have a high-pass RC circuit setup. My problem is that when I send in a 120mVpp sine wave, I get a 160mVpp sine wave as the output, without the DC offset. I'm trying to be as accurate as possible. I'm using metal film resistors that have 1% tolerance and LM324 op-amps (with +/- 15V). C_highpassfilter = .1uF, ceramic. R_highpassfilter = 1Meg. Anybody know the problem?