Yes, you will.... you turn one up and odd, lower signal levels start appearing on other busses, 'out-of-phase' and seemingly randomly associated...
So you first need to determing what mods are present in the base console modules, there may be AFL mods etc...
Then you need to make sure that you're adding the SAME revision of lower buss cards on the extension section.
Then you need to perform the "coat-hanger" modifications to the older ("brown-EQ") modules... Notice that the black, stiff wire (looks a bit like the stuff that wire-coat-hangers are made from.. hence the name) -that sits on top of the 611 motherboard and runs underneath the daughter cards- will be different on the new and old cards.
The newer (split-ground) modules will have:
1) Different ground 'coat-hanger' layouts
2) A little "ladder of about five resistors standing upright and joined together at the upper end, near the upper buss card edge connector pins
3) A cut in the really thick PCB trace, near the resistor "ladder"
4) usually a small jumper in the same area, which allows you to 'bridge' the PCB ground trace cut, for using the modules in split-ground installations, without ruining the grounding scheme.
You WILL need full documentation to do the mod, missing a SINGLE step on any ONE module will mess up the whole console whenever that module is inserted.
-But it's not that tough though, just needs some patience.
I can probably help out, and I'd be happy to do whatever I can... -specially if there are any juicy spares left over in that '81 center section! :wink:
Keith