OK, so I nicked a friend's MXR Phase 45 to try with the ModFactor. For the few not in the know, the Phase 45 is a two-stage phaser with just a simple speed knob. Ran guitar –> Phase 45 –> ModFactor on default Lou-nivibe settings. Set the speed by ear as close to the 2.8 Hz of the Lou but, obviously, they're not in sync like in the real Uni-Vibe. It didn't really work, because they weren't in sync, but the results were quite interesting, even if over the top and too much. When the two would briefly sweep together, it was closer to the target sound than just the Lou alone. But when they were sweeping against each other, way too much fast w-w-w-w-w-warble. Similar to going to four stages via the Xnob on the Lou setting (even when the speed is reduced a bit).
It was an interesting experiment that really shows all four stages need to be swept together (as the four LSRs in the common light box driven from the one lamp ensures). With two ModFactors or two H9s, I'm not sure if tap tempo via MIDI would be the proper way to sync them. Even if this were possible, it may be too "perfect" as well since the slight differences in response times of the LSRs, while keeping the stages moving together, provide some variance to make the overall effect more rich and interesting. I've noticed too that when either the real-deal Uni-Vibe or my clone was engaged for some time, the effect would change (the speed seemed to increase ever so slightly) so I wonder if the lamp's response changes a little as it gets warmer over time.
Back to the drawing board to think about this some more. I guess I'll flip back to my Binson Echorec clone (four BBD delay lines with extended but equally-spaced times out to about 500 msec, toggle switches to select any combination of the four delays, cascaded FET preamp) for a while!
