ARDUINO DAC

30kHz filter corner is much to high for a 30kHz input signal. Go ten times lower as thumb of rule to get with an passive 1order low pass, or even better if you already power an OpAmp why dont you implement a second order lowpass ? Anyway, you know the default PWM signal is about 400Hz and only with some ugly tricks you can increas it to about 30kHz. So a good filter for arduino is somewhere below 100 or less in corner frequency by default. This is still good for >20ms settling time. It all needs attention to the ripple which is left after filtering. E.g. if the PWM is a 8bit resolution we need a filter with about 46dB attenuation to all harmonics is sum inclusive the base harmonic 420Hz for arduino, otherwise we lose performace from PWM to DC voltage we would like to get. 48dB is from 5V / ~250 = <20mV ripple

yes, your amplifier gain is 5

and as you can see in bode plot the corner frequency for this combination 10kOhm 100nF is at 159Hz http://everycircuit.com/circuit/4688521158459392