Finally getting back to these. Haven't really sourced or stuffed much yet. Broke down and ordered the other pots from banzaieffects.com; I never found any appropriate US source.
You want shorting (MBB), otherwise the momentary open circuit of a non-shorting causes a gain fluctuation. Shorting simply parallels filter sections momentarily.
Sounds like Denyle is bypassing between the 620 and the 5100 ohm shunts at in and out of filter section. Should be able to add a single series resistance between those points to match gain at flat filter setting. Though, you might want to make a T attenuator to keep Z more inline with Z within filter, since we have 1K and 2.2K to ground in the filter.
The burning up and overheating is curious. It looks to be fool proof in regards to opamp input loading and bypass condition. That was the first thing I thought of, bypass connections that left that opamp input unloaded. But that doesn't look possible. Makes me think overheating is an oscillation caused by lack of a ground connection somewhere.
10K boost on bass should only reduce gain somewhat, when set for no boost, greater and sharper boost possibilities. It might not work well, but I don't imagine it would cause serious problems.
Has anyone with a working unit, having bypass, felt the desire/need to change the opamp gain setting? Curiosity question.
I paralleled some small film caps with the pair of 2200's and the 47. Did it underneath the boards, between the board and the metal frame. Maybe a bit tweaky, but I like to do this.
