The topology on the 163-using boards looks like this:
Code:
famicom : cart : famicom
+--100k--+ : 163 :
| | : | :
C--+--|>o---+--:--R--+--:--RF modulator
| : :
DA15
(edit: added location of Famicom expansion connector sound)It
should be the case that any given size of resistor should make the NES audio quieter proportionate to its conductance (1/resistance).
Unfortunately, the resistor values we've observed don't correlate with the reported loudnesses. So either the reported resistors are incorrect, or something even weirder is happening.