What is the temperature and supply drift of the circuit?
Hi-Q opamp circuits, by themselves, do not have good frequency drift
compensation over temperature. That is, as the temperature changes the
components' characteristics change and the filter's response frequency changes.
Thus the filter can "drift" off the desired center frequency.
The MAX 275 we use has a temperature drift compensation feature built into the
chip. For details, look at Maxim's website:
These cite +/-0.9% from center frequency drift over temperature range
Our frequency drift at 24.8 KHz can be +/- 0.22 Hz --- less than 1 Hz!
MAXIM also cites power supply noise rejection at -30 dB (100mV-pp @ 1KHz)
Our SID Manual also gives further details.
MAXIM 4th- and 8th-Order Continuous-Time Active Filters