[gguy]

I have a new amplifier and am trying to determine the correct value of the capacitor to get for a passive crossover.  Having done this before on my last amp, the input impedance was a single value and was pretty straight forward.

The new amp that I have appears to have the input impedance on a curve:  Min. 15K at 50Hz; 23K at 1Khz.  Any recommendations on what value capacitor I should be getting to crossover at 75Hz?

[cjsailer]

I don't know much about audio, but why are you talking about a crossovers in relation to an amplifier?  What advantage is there in optimizing a crossover for a specific amplifier?

[Hobbsmeerkat]

Im guessing you're talking about a high-pass filter to take the lowest frequencies out of the signal being sent from your preamp to your power amp?

[gguy]

Im guessing you're talking about a high-pass filter to take the lowest frequencies out of the signal being sent from your preamp to your power amp?

Correct, I am trying to make a high pass filter from my preamp to amplifier.

[mlundy57]

At 15kHz a 0.10uF cap will be -3 at 106Hz
At 15kHz a 0.15uF cap will be -3 at   69Hz

At 23kHz a 0.10uF cap will be -3 at 70Hz
At 23Khz a 0.15uF cap will be -3 at 46Hz

My guess (but I'm not an engineer/designer) is that based on your amp's specs a 0.15uF cap will get you closest to 75Hz.