-> I think the Strat Plus and Ultra have passive boost/cut tone
-> controls. Technically, you can't actually boost with a passive
-> circuit, but the center detent is "neutral" or "10" on a normal tone
-> control.
The TBX is a combination 250k and 1-meg pot.  After the detent,
the 1-meg pot kicks in.  It does add bass and high-end passively after
the detent.
The Delta-Tone (newer system) effectively takes itself out of the
circuit after the detent. That also adds low and high-end in a passive
manner.
Tonally speaking, of course :))
--- FidoPCB v1.4 [fb34e/D]
---------------