Amp and preamp impedance

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

Have you considered purchasing the MIT oracle interconnects they have a three step impedance variation switch so you can match any preamp and amp combination. I only went this route as I wanted to run a tubed preamp ARC MRKIII with Krell FBP 750MCX mono blocks and Krell requires you to return the amps for a factory MOD in order to mate them with a tubed preamp. Oh and please put aside the stigma regarding the MIT networks these interconnects sound incredibly sublime.

Definitive