Is there a calibration procedure document, for the Doepfer A-131 exponential VCA

I bought one used, a while ago, and I've never been sure it's set up as it should be.  It tends to go from a little bit too quiet to way too loud, rather suddenly, making me fear for my eardrums, on headphones - which makes me wonder if the previous owner fiddled with it, then gave up on it.

- Andy