Quick description: Input signal is .2V pk-pk. Voltage after amp is 4V pk-pk. 2N7000 needs 2V to turn on, so it should turn on when the frequency I want is passed through the filter, but any other frequencies are decreased in amplitude.
My problem lies after C2 at node Va. What I expect there would be an amplified wave of my input centered on the x axis (if the y axis was measuring voltage.) Instead what I find is my amplified input shifted up by 1 or 2 volts. So even though my AC signal decreases at node Vb as frequency increases, it is still biased by that +1 or +2 volts, so the MOSFET stays on at all frequencies.
I've tried a number of things so far. First, I tried discharging the caps, but that seemed to have no affect. I tried adding a large resistor in parallel with C3, but that didn't help much either. I really don't know what's going on here or how to fix it, so any help would be greatly appreciated. Thanks in advance!
EDIT: I also chose large values for my filter because previously it was too small and the lack of impedance was causing a voltage loss at higher frequencies. I am also aware of the nasty clipping my amplifier gives me at the moment. I plan on fixing it later.