Hey Harpo,
I've been able to do a test after I've desoldered the 47R which was connected to pin 4 of the turbo 2180, following your advice. So what I can say is that there is still a difference between left and right side when fully panning from left to right. The difference is not as big as when there were the two 47R but approximately, left side is compressing about 6db more then right side when fully panning my master channel pan knob.
So I was guessing if maybe another resistor needs to be unconnected to the 2180 as I saw on the GSSL schematic that the side chain VCA is a 2181. So is the difference between 2181 and 2180 only that one is pre trimmed and not the other? Anyway, this won't help me figure out what is going wrong... What I can say is that the turbo board's side chain still hasn't the same values than the one on the main board as the signal is not treated the same from one to the other. I saw on the GSSL schemo that the 10k connected to pin 5 of the VCA is also connected to a 3k9 resistor but on the GSSL layout it's a 5k1, so Harpo, do you think this could make the difference? I checked on my turbo board and there's a 3k9, so do you think I would have to change it for a 5k1?
I think it would be interesting that people who installed the turbo mod in their GSSL with 2180 or DBX 2150 could make the same test and give some feedbacks about what happens when inserting the GSSL in the master output of their mixer or sound card, and mute one side then the other and see if the sound is the same both sides... Or is it just me who experience this strange behavior???