Yeah, unfortunately I had to use a different op amp as the 971 isn't in Multisim. Rather than search for a low noise, low power op amp in their database I just went with the first one that came to mind!Multisim shows (severe distortion) that a lousy old 741 opamp (45 years old) does not work when its supply is less than about 10V.
I'm still getting a bit of a jump/error in and around 2Hz at the start, but it sorts itself out fairly quickly to a near perfect state. I figure that's either down to the op amp being used or some time that is needed to charge the capacitor, does that seem right?
Having used:
Gr = 20 * log10((w * R * C) / (sqrt(1 + (w * R * C)^2)))
and a range of frequencies from 1-100Hz (w being 2*pi the frequencies) and plotted in MATLAB, I'm fairly certainly the component values are correct now.