This circuit was invented by Dr. Horst Ludwig from Germany and published in September 1992 in "Stereoplay", a German Hifi magazine. It's an additional board that should work with all DAT decks that have a Sony CXD2601 signal processor IC inside (many Sony DAT-decks and the Pioneer D500). It was tested by Dr. Horst Ludwig with the Sony DTC-55 and 57 and it works with my Sony DTC-670. Chances are good that it will work in other decks with a CXD2601, but I'm not sure about that. (So I can't answer questions like "Will it work with my Sony DTC-59?"). Don't blame me if you ruin your deck. I don't even fully understand what this circuit does. (Maybe someone else could explain this!?) Modifications at your own risk!!
The installation picture shows the additional board built into a Sony DAT-deck and on the close-up picture you can see the connections to the Sony board. (There are three cables going to the CXD2601 and the other two cables are for the 5V power supply of the board.)
You don't need to change anything on the Sony board. Just connect the new board. The SCMS code on recordings made via a digital input is set to 00. (Recordings via analog input have 11!)
There are three images which are available: