Univibe Chorus/Vibrato switch...can it be swapped with a pot for blending?

[Nocaster Cat]

Trying to think something through and I may be way off so I figured I'd ask. I've looking a Univbe schematic and I "think" when switching to the Vibrato setting a 47k resistor comes into play. Could it be swapped out for a pot (and the appropriate connections made at the switch as well) to allow for blending between the Chorus and Vibrato settings or does it have to be one or the other? Thanks!

[R.G.]

Anything audio can be blended to anything else audio if you want to work hard enough at it. It's the details of what, exactly, that "... want to work hard enough at it" will mean.

Here's the tech scoop. The Univibe (and all other normal phasers) generate a version of the input signal that has a variable phase shift when compared to the original input signal. This phase shifted signal, when swept by an LFO, sounds like a "vibrato" as the human ear hears the change in phase as a change in frequency. In the Univibe, this is output at the "vibrato" setting by scaling it down a bit with resistors to make it smaller.

Again, all phasers mix the un-modified input signal with the phase-shifted signal to make the notches in frequency response that the human ear picks out as the phaser sound. How deep and aesthetically pleasing this phaser sound is depends on many things, but most notably getting the mixing just right to have the (mostly) unmodified input signal and the phase-delayed signal just exactly cancel each other at certain frequencies. If you change the amount of either one much, the phasing gets correspondingly fainter.

The "chorus" setting of the Univibe is just this - the phase delayed signal is mixed with the (mostly) unmodified input signal in the right proportions to cancel at the right places and you hear phasing (not "chorus").

So Univibe "vibrato" = "phase shifted signal" and Univibe "chorus" = "phase shifted signal" + "dry signal". If you blend between them, you are really just changing the amount of dry signal in the mix from 0% up to whatever constitutes a 100% for phasing, plus perhaps doing some unconscious but fortuitous level changes to keep the overall volume mostly unchanged. You could mix in the dry signal inverted compared to the real input signal, and this would change things a bit, but it amounts to shifting the phase cancellation notches a bit, not much audible change.

The trick will be to mess with the four or five resistors that do the two outputs, one a volume reduction for vibrato and one a mix of dry and shifted, and keep the levels the same. Before you commit to hard-modding your board, it would make sense to take some kind of mixer and tinker with it to see if you get the kind of audible mix you expect.