I have a question regarding RC filter designs. I have a system that picks up an analog signal at 200Hz and I'm passing the signal through a two stage low pass filter and then a two stage high pass filter. Currently I'm using a 0.1 µF capacitor and a 4.6k resistor for the low pass stages (346Hz) and a 0.1 µF and a 10k resistor for the high pass stages (159Hz).
I'm losing a lot of my actual signal and I'm wondering if I need to be considering some different components.
The signal coming directly out of the amplifier chip (INA128) reads a peak to peak swing of about 3.5volts. It is powered by a true split supply rail +/-9V. The signal after the filtering is somewhere in the neighborhood of 300mV. So what am I doing wrong on the filtering? Any ideas?
EDIT: Filter Design image added. Pin 6 at the top is the output pin from the INA128. The left trace to the capacitors and resistors are the Common rail. You'll notice that there are two 4.7 zeners on the output (to protect against over-voltage to the ADC chip downstream) and the final signal is getting passed to an ADS1015 analog to digital chip. (I know, I'm losing my negative signal on the ADS1015, but that's not really important data in my circuit. I'll tackle that later with a true split rail ADC chip.)