I have an aikido preamp running on 24v with ecc86 tubes. The front of the preamp has a 10k r2r attenuator and the preamp feeds into a class d amp(CDA254). The amp has an input impedance of 7K and demands that the preamp should have an output impedance of less than 600 ohms. The problem I am having is selecting the output cap of the aikido. Based on the calculations, for 5Hz cutoff, I need a 4.5uf cap (1/159155/r/f). When I used a 4.7uf cap (blackgate N), the sound was thin. I replaced it with a 10uf cap and Iam getting bloated bass (kind of slow and high frequencies attenuated). There is something wrong somewhere either with my selection of capacitor or probably the choice of attenuator. I use to run a class AB amp before and it sounded great with 4.7uf cap. I would greatly appreciate if someone can help me out.