Happy New Year!
Interesting. Perhaps do you have more info or a diagram on how eactly did Alembic do their buffers and what are you reffering to as a "humbar"?
Dutch magazine Music Maker did an article about this circuit long ago, complete with the buffer stuff etc. I could scan if still needed.Much later on (after having perfboarded it back then) I noticed that the article-schematic had an error, will indicate that with the scan.
Clearly, this is the "father" of the tubescreamer. It says "4558" and it has the filter.
Well - that was meant as a mojo-joke.
I was naively hoping the "humbar" to be the nulling technique as you described on previous page (with unity signal being fed into the "casing") ...
In that one particular bass I have older bart stacked j's. They are pretty sensitive for CRT and similar noise.
I wouldn't order a special smt filter do-dad.
The reason for smt bead should be so that I could simply solder two 0603-size caps on it and the whole thing would be both very small and sturdy, ready to be dipped in resin so it will all be practically seamless from mechanical p-o-v.