The mighty H9 CAN do this … using the PitchFuzz algo.
The way I think of it is you have to selectively pinch off the signal running into a delay while always allowing a dry signal pass through. In PitchFuzz, you set pitch voices A and C to off and set pitch voice B to “0” (no harmony). You set the delay B time and feedback as desired. I have the ARP LEVEL set at 27 ARP WET. Then set the PITCH AMOUNT for expression control to range from about 0.8 to 1.8 “voices” (voice A is always on and voice B blends in). My expression pedal has a bit of slop in it so this range ensures proper response.
Set like this, voice B is a non-harmony delayed signal that is in parallel with your dry signal (voice A) and controlled by your expression pedal. This is very clear to see in PEDAL VIEW.
In total, my setting are:
OFF … 0 … 0.8-1.8 …OFF … 0 … OFF
ARP WET 27 … 450ms … OFF … FB1:44
On a related note, I have suggested that EVENTIDE add this feature to the ULTRATAP algo. In ULTRATAP, the bottom right control is entirely “unused” while the “chop” control is “off”. This “unused” control could be an expression-pedal-controllable “input level” control for the delay (while not affecting the level of the dry signal at the output). Since this knob has always been “unused” in this algo, this change would be backward compatible with all prior presets. ULTRATAP is a great delay and It’d be great to have this feature there too. So far, It looks like I’m the only one that thinks this is a good idea.