Amp and preamp impedance

Typical is almost irrelevant. If you want the filters to have any accuracy, you should know the impedances of your particular components. Of course, you can define characteristic impedance of the network at intermediate values but you'd still need to know what you are starting with.

I agree with the previous advice. The response of a filter is dependent on the impedance of the source and the load. I admire your DIY spirit but I think you need to do a little more research into the problem. There are many fine electronics textbooks devoted entirely to filters where you could begin. First order filters are relatively simple, but beyond that it gets rather complicated. Good luck.

I just want to make a simple RC network (1st order) and I need to have some idea if there's a value for the resistor that would be large enough to be easy for the preamp to drive and small enough to make the input impedance of the power amp irrelevant.

Both preamp and power amp are solid state and I'll be using single ended inputs.

For a first order high pass filter you only need a capacitor in series with the input of the amp.

A typical value for the power amp input impedance would be 50K. But as stated above, typical will do you no good since they range from 10K to 100K and the cutoff frequency is directly proportional to this value. You need to get the input impedance for your amp.

fc=1/(2RC times pi)

If I might jump in on a related question, I am trying to do the same thing. I know the output impedance of my preamp (200 ohm) and the input impedance of my Pwr amp (22 K ohms - single ended). When I use conventional passive crossover design calculators for figuring out a 2nd order low pass butterworth filter, I get ENORMUS values for the inductor: 4700 mH. Can this be correct? Where is a good source of the formulas that I could use for designing a passive line level crossover for biamping? Does the output impedance of the preamp figure into this at all?

thanks -- Roy3