Wish I could tell you exactly. All I can remember is that it involved changing out the rear panel, as the arrangement of the connectors was different. The PCB was obviously different.
I do remember that it happened around the time he came out with newer versions of the FET-I and FET-II preamps. I seem to recall that those upgrades used some small-signal MOSFETs in the gain stage. I do not think the S-300 upgrade was as extensive as the preamps were. But that was over 20 years ago.
I do remember that it happened around the time he came out with newer versions of the FET-I and FET-II preamps. I seem to recall that those upgrades used some small-signal MOSFETs in the gain stage. I do not think the S-300 upgrade was as extensive as the preamps were. But that was over 20 years ago.