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In the Forum: Melquiades Amplifier
In the Thread: 6 Channel Version of Super Melquiades
Post Subject: Not a Single ValuePosted by hagtech on: 1/23/2008
The answer will be a complicated one, as the preamp is driving an active crossover.  The many storage elements means the impedance is a function of frequency.  There is no "10k ohms" answer.  I hope you are driving these network with something powerful.

You could always simulate the elements in SPICE.  That could give you a Bode plat of impedance amplitude and phase, just like the graphs seen in stereophile.

I do something much simpler, and will give you an approximate result.  Put a small capacitor in series with the input.  Say 0.022uF.  Measure the LF -3dB point.  This highpass filter will rolloff at 800 Hz for a 9k input.  Similarly, you can measure the output impedance of the preamp by adding a cap to ground, measure the HF rolloff. 

R = 1 / 6.3 * f * C;

jh

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