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RE: Zin = 33kohm...

Yes. I'm thinking that is the value of the resistor to ground that follows the coupling capacitor.

I don't think the effective impedance to ground of the first transistor can be measured with a ohm meter and I'm thinking that impedance would only show up once the amplifier is turned on and current is flowing through the first transistor.

If I'm right, that would answer why they used such a large input coupling capacitor.

You could go about this empirically. If you replace the 330uf cap with a 1uf cap and then play the amp. Use a signal generator and measure the -3db point.

You can then do the math to calculate the impedance.

If, as an example, with a 1uf cap you find the -3db point to be 159Hz then the input impedance is 1000 ohms.

Tre'




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