How to calculate gain for the following LPF Op Amp circuit? what value need to be changed to get mor

As drawn this circuit will have an amplification of 1 * (V2 - V1).  But with power supplies of +/-12V you should be able to get an output of +/- 10V without problems.  So I assume you have a very low input signal that needs more amplification.  From the diagram it looks like it gets its input from a DAC and most DACs will output 0 to 5V or 10V, but maybe you're using it for other things?The gain of a differential amplifier is complicated, but in this case if R53=R223 and R56=R67 then the gain simplifies to R53/R56, so in this case with all these resistors being 2.4K, the gain is 1.  If you were to change R53 and R223 to 4.8K you'd get a gain of 2, (R53/R56 = 4800/2400 = 2).  It is important that R53=R223 and R56=R67 as closely as possible, use 1% or better resistors if you can, and don't try to squeeze too much gain out of this circuit, I'd use 10 as the limit.In reply to a recent question my fellow (and much more savvy) expert Elizabeth posted this link which you may find useful:https://www.electronics-tutorials.ws/opamp/opamp_5.html

The MFB filter gain is set by the two resistors mentioned, but the cut off frequency and Q are affected by these resistor values as well, so you may have to redesign the whole filter for higher gain, or the Q and cut off frequency will change. If this is not an issue  then the previous comment stands.There are many app notes to be found on the web for designing MFB filters, Texas Instruments have one, http://www.ti.com/lit/an/sloa049b/sloa049b.pdf
and there are free filter design apps out there, for example     http://www.schematica.com/active_filters/fwlite.htmlYou can check your design in LTSpice, which is also free.Cheers,Richard

Hi David,Thanks a lot for your suggestions and useful resource. Much appreciated.  Yes the input is from a DAC with 3.3V . As with the other comments, it looks like i also have to recalculate the C for Q and fc. but this is a good starting point ! 
Thanks again! 

Hi RichardThanks for your suggestions and design resources! Much appreciated. So it looks like i have to redesign the whole filter circuit! are you suggesting to change the Cap to maintain the Q and fc? using the equation  fc= 1/2*pi*C34*C35*R56*R55? 
Thanks again!

Hi Kris, without knowing what you are trying to achieve, I am loath to offer too much advice.   Q and Fc are determined by different equations, and relate to  pole locations. These are what determine the class of filter, in classic filter theory these would be Bessel, Buttterworth, etc. The filter you are using is a second order type. The MBF filter type is perhaps the most difficult of the common active filter types to design, since the interaction between components is extreme, however, having an amplifier configured in an inverting mode has the advantage over a non inverting configuration like the Sallen Key in that the output impedance of the op amp  does not interact with the feedback network to reduce filter attenuation as the frequency increases.It would help if you could provide more details, such as the DAC p-p output, and what you actually need. as well as more details on the type of DAC, the clock rate, and the desired bandwidth are.Cheers,Richard

Hi Richard,

Thanks, I am using TVL320aic34 DAC with
3.3v p-p, 96Khz clock rate. my design is a two pole Bessel filter, low bandwidth -3dB at 100hz, the LPF filter is
for motor drive for a gyro sensor.  Regards

OK, since you have defined your filter response and cut off, I suggest you go to Texas Instruments web site and download FilterPro v3.1 for the desktop, work through it setting up your parameters as you go, it is fairly self explanatory.Key parameters are In the setup, step 2, put ingain=5v/vpassband=100ripple=0filter order fixed at 2On the last page, where the output is plotted, you can set up the Rs and Cs with a tolerance, say 5%, and look at the change in the filter response. You will find that you can get away with off the shelf values quite readily. Don't use ceramic capacitors where dc is present, they have a terrible capacitance/v variability.cheers,Richard

Hi Kris,just realized that your question needs clarifying,  what voltage swing do you want at the output of the filter, and does it matter that it is inverted with respect to the input, the figure of 5v/v  in my last comment is not correct,cheers,Richard.

Hi Richard, I want more gain  to produce +/-5v from what I have right now.I will try the filter pro from TI! Thanks again for you kind help.Regards