So, it looks like the mojo in the 670 is that it adds a touch of harmonics. Until the gain reduction kicks in, then it takes off. Sometimes I like to use this across a bunch of channels, so I can feel like I have a dozen or more Fairchild’s sitting in my rack. I then go out and sell them and retire.
When you see the high end drop like that, it’s not part of some “analog emulation” — it’s the filter to keep it from (digitally) aliasing! You can compare this to the Waves Puigchild 670 plugin and read some further comments about it there.