Phono Stage Question.....

Sutherland, to the best of my knowledge, did not invent the idea of current drive.  As noted elsewhere, every current driven phono stage is going to sound a little different with any given cartridge.  This is my experience as an owner of a BMC MCCI, and after comparing notes with other owners of other current driven stages. My guess is that this is because none of these devices is "ideal"; an ideal current driven stage would have a zero input impedance, and that is not possible.  Hence they all have slight differences in input impedance, ranging from a few ohms to as much as 20 ohms.  This impedance will interact with the internal R of the cartridge, resulting in slightly different gain characteristics and possibly in sonic character as well.  Another factor affecting SQ is the fact that these devices consist of a current to voltage converter input that adds gain via amplifying current but puts out a voltage to drive the downstream circuit, which must be a conventional RIAA filter operating in the voltage domain, and the output is ultimately a signal voltage. Nothing is perfect. In my opinion, one should not assume that current drive is some sort of panacea for problems of cartridge loading (and only relevant to LOMC cartridges with very low internal resistance).