Hi,
will higher capacitance cause a DC error ?
No.
Only the leakage of the capacitor may cause problems..
Use high quality polystyrene, if possible.
I removed the diodes and my linearity fell into spec..
* The diodes are for "protection" only, not for rectifying..
* use "low leakage" ones.
* they should have no influence on function, nor noise, nor linearity
If there is an influence, I expect a design mistake elsewhere.
I recommend to post a photo of your amplifier circuit, where we can see wiring, power supply connections, all GND connections.
Urgent design requirements:
* GND plane, inelligent star point type GND wiring
* properly HF decoupled supply for the OPAMP
* I recommend to supply the OPAMP from a battery, if you use any other supply you need a high quality one with low and low leakage/ low capacitance to mains
* properly decoupled and properly low pass filtered HV supply with f_cutoff_supply << f_cutoff_of_amplifier
Klaus