Passive Line-Level Crossover

to try to calulate it and checking with the xls from this diyaudio post:

http://www.diyaudio.com/forums/multi-way/12990-pllxo-v-axo-v-pxo-benefits-model.html#post2356273

Ill be using a triode st-70 clone for the highpass amp, which pages found on google says has an input impedance of 470K.

I'm trying to make a second level lowpass at 110hz and a second level highpass at 400hz.

Low pass seems straighforward, my results coincide with the xls.

R1 5.0 k

C1 289.37 nf

C2 28.94 nf

R2 50.0 k

**The problem is in the second level high pass**.

R1 and C1 are based on the values from the lowpass filter, as I've understood.

Calculation of c2 isn't clear. The issue is the text of the last paragraph:

"If the input impedance gets lower, this has two consequences: the insertion loss gets higher and the xo frequency is shifted upwards. To compensate, calculate C2 in the lowpass as follows:"

I believe this should read ..."calculate C2 in the HIGHpass as follows:"

However, I am not sure if C2 is right in the sheet, it reports .01pF.

The R2 I have calculated is different than the sheet. In fact in the xls, changing amp impedence doesnt affect the R2 value at all, but based on the formula it seems it should. Im getting 56k in my calculation, the sheet gives 50k.

Could I ask someone to help me determine the C2 and R2 component values in a second level highpass PLLXO at 400hz, with an amp impedence of 470k (I hope this figure is right)? With the final results, I can check if there is an error in the xls or if its all correct.

Later, I want to also make a highpass for an audiosector LM3875, but so far haven't found its input impedence documented. Is this documented anywhere or will I need to calculate it?

Thanks!

Andrew