Sallen key problem stability

[worldcup34]

Hello! I am developping a filtering board for analog signals (bandwidth of interest 300-5khz). I used for this purpose a lowpass Sallen key, a high pass sallen key (all butterworth configuration) and a passive RC low pass for adding a pole. I tried various Gain (3,5 , 5 ,8) on a breadboard and they all seemed ok but when I tried Gain = 10(10 for the first SK and 10 for the second. So the total is 100) I noticed a strange behaviour. (see the attachment - the comparison is with the Ltspice simulation). The strange thing is that if separated the two sallen key don't show any problem...
Could be this due to sensitivity of circuit parameters to tolerance components ?
Is maybe the impedance of the passivr RC too low ? It's only 143 ohm cause after that should be linked an ADC with impedance of 10khm
THX!

 

[Winterstone]

When you have designed both stages for a Butterworth response you cannot change the gain of the opamps without disturbing the desired characteristic. Increasing the gain will cause a drastic change of the pole Q.
Recommendation: Try to become familiar with design of these filter stages or use an appropriate filter design program.

 

[crutschow]

You might download a free copy of FilterPro from Texas Instrument. It greatly simplifies the design of various types and orders of Active Filters.