It's not the same layout but I built the ROG Umble yesterday. It has 4 J201s that you need to bias. It could be the fact that the 100k trimmers have a huge range that it was quite difficult to bias them. First half or even further of the trimmer didn't change the voltage much but then by just barely touching it, the voltage jumps. In the end with a little patience, I got them all between 4.45 - 4.55v.
I'm thinking of building the Dr. Boogie soon so I'll report back when I have.