The Turbo is a PCB which will contain the second sidechain to allow the GSSL to work in EITHER 'Oxford' (SSL) mode or 'Aarhus' (GSSL) mode.
It is a much simpler build than the current "two-full-PCB" way of doing it, and comes with simple instructions explaining how to connect to the main unit, using three small header connectors.
It can EASILY be retrofitted onto the a modern GSSL build, or an old one from 5 years ago.
You'll be able to "bolt on" a turbo to ANY GSSL, and it will be compatible with any sidechain filter PCBs... you'll just need to add a second sidechain filter PCB for the turbo sidechain as well.
User Manual can be downloaded from here: http://expataudio.com/diy/Turbo/TurboInstallationManual.pdf
A Mouser Bill of MAterials can be found here: