The 'amp's resistor' does not make a lot of sense in this conversation. However the 'cartridge loading resistor' does and that is what I meant. If it is in place prior to the application of mechanical damping, it may well be found that the damping of the resistor was compensating for the distortion (which will cause brightness) present when the arm, vinyl or turntable was not damped.
So the result would be that by doing the mechanical damping it might sound dead and lifeless. I've found that if your electrical/electronic ducks are in a row, its impossible to overdamp a platter, overdamp an LP with a platter pad (although a platter pad causes changes in tonality all on its own) or by properly damping an arm tube (which admittedly is a bit of a trick, as this directly affects the effective mass of the arm/cartridge combination).
So the result would be that by doing the mechanical damping it might sound dead and lifeless. I've found that if your electrical/electronic ducks are in a row, its impossible to overdamp a platter, overdamp an LP with a platter pad (although a platter pad causes changes in tonality all on its own) or by properly damping an arm tube (which admittedly is a bit of a trick, as this directly affects the effective mass of the arm/cartridge combination).