Audio Research SP-6C vs. SP-6C-1?

What is the difference between Audio Research SP-6C vs. SP-6C-1? I try to repair my SP-6C-1 preamp, but can't find any schematic drawing for this item.
I will have to look but I believe the difference was the removal of a regulated stage for reliability issues. If I get a chance I will compare both and let you know.
I was not supplied with a C-1 circuit diagram so I am assuming the C-1 and the E are similar. Power supplies are the same. The only differences are as follows: The C uses diodes for current sources, The E uses Fets. The C ver uses (2) opto couplers. The E ver. uses one. Both versions use 6DJ8/6922 for both high level and phono cathode followers.