Sallen Key Low Pass Filter cap reference significance

[knutolai]

Hey

Very fond of the sallen-key low pass filter. This may seem as an odd question, but would there be any conceivable difference in the performance of the filter if the C1 cap is connected to virtual ground (4.5V) or real ground (0V)? My thought is that as long at the cap value is small-ish the DC leak will be negligible and thus real ground would be the better option in terms of impedance. However using a buffered virtual ground (as in the schematic below) with a low output impedance opamp I assume it will make almost no difference what ground is chosen?

EDIT: Had the wrong cap reference. Sorry..

[antonis]

Are you actually wondering about C2 or C1..??

[Rob Strand]

In an ideal world it makes no difference.

However, if you use ceramic smd caps it can make a difference.  When connected to ground the cap has larger DC voltage than when it is connected to Vref.

Read-up on voltage dependency of ceramic SMD caps.
The capacitance can decrease with DC voltage.

[knutolai]

Are you actually wondering about C2 or C1..??

Oops fixed