We've seen how the RIAA filter behaves with low and very low capacitor values. (See all simulation articles here) Now let's have a look at what happens if the capacitor values are higher than the recommended ones.
This is the Muffsy Phono Preamp with capacitor values that are 2.5% higher than specified.
As with the simulation with lower than recommended capacitors, this shows that we're still following the RIAA curve quite nicely even though the capacitor values are slightly wrong.
Now what happens if we bump the caps up to 10% higher than the recommended values?
The lowest level is -0.535 dB, and the highest is +0.186 dB. The average deviation is still only +/- 0.36 dB. There will be a slight attenuation of mid bass and the higher frequencies though, something that will become apparent if we really try to exaggerate by changing the capacitor values to +25%:
All the mids are attenuated and so is the treble, while the low bass is amplified a bit. +0.44/-1.16 dB is not something you'd want in your phono stage under normal circumstances.
A Conclusion...
The best scenario is to use the specified capacitor values, or within +/-10% of these.
Deviations that are extremely low will give you a slight "loudness" effect, while extremely high capacitor values will attenuate the mids and the treble. Luckily, these extreme values won't enter your phono stage unless you do it on purpose.
These are also all good examples of what hides between the RIAA compliance numbers, that vendors seldom show in detail.