The input impedance of the amps measure about 100k. So that would put the total input impedance of 100K + 47K = 147k?

I've built 4 attenuators of various values so far using cheap Radio Shsck resistors. It seemed a reasonable assumption that cheap resistors would sound better in the circuit than cheap pots.

Yet every one of the attenuators (on tube and solid state amps) seems to have an overly strong attenuation in the treble. Could the cheap parts be the issue or is it more likely that I still haven't gotten the impedance issues ironed out?