Input impedence? What makes you think the Carver is different from most amps out there? If it follows the norm, input impedence should be in the neighborhood of 50K. The odd amp here and there might have an input impedence of 20K and I've even seen a few at 10K, but 50K is almost an industry norm.
If you really, really need to know, it can be discovered with a pot in series with an input signal...a tuner would work well for this. You'd need to hack an phono cable and install a potentiometer in series with one of the output channels (100K pot). Turn off muting, and dial in a point on the dial with no station (close to pink noise source, some call it 'rose' noise). Measure output of the tuner at the tuner with a DMM (we aren't splitting hairs here, so meter frequency response is a non-issue). Set it to something like .5V RMS or so (you may not want speakers hooked up). Now measure the voltage across the pot. Set the pot so that half the tuner's output voltage is dropped across it. When you have achieved this, disconnect the pot and measure it. This will be the input impedence of the amp.