Extra Stages in a Univibe

[Storing!]

I'm building a Univibe and I'm toying with the idea of adding 2 extra stages.
Did anybody try this and... the big question. What should the values of the caps be?

[Jaicen_solo]

I'm pretty sure RG designed an ultra-univibe with eight stages, but I don't know what happened with it.

[Mark Hammer]

I'm not so sure there is much benefit to adding stages.  The Univibe sound is really more one of some subtle shallow and broad "scoops" being shifted around.  Where adding more notches to a true phase shifter (where the notches are more focussed) is usually able to intensify the effect, this is unlikely to be true for a Univibe-type circuit.  The "unfocussed" property is also the reason why you've never seen a Univibe with a feedback/regen/resonance control.

[Storing!]

Well, the idea came from the article about the vibe of RG on Geofex. He mentions an ultravibe with extra stages. Couldn't find any further reference though. The six stages come from the fact that I only have room for 2 more (very tight build). And the MOOG phaser is also a six stage.

Still makes me wonder which way to go. Marks post makes sense. Maybe any ideas what to do with the free veriboard space?

[Mark Hammer]

If you wanted to provide some means for changing between 6-stage phaser and 4-stage Univibe, then certainly adding more phase-shift stages isn't a bad idea.  Note that you would have to:

• switch in the extra 2 stages
• change the cap values from staggered to identical and vice versa
• provide a means to add regeneration/feedback for phasing and lift it or reduce it to nil for Univibe mode

It can be done, and people HAVE done it. but it won't be all that pretty a wiring job without careful planning.  If the intent is to have a dedicated Univibe, then my sense is that adding more stages will not improve it much if it improves at all.  Phase-shift is like chillies, where adding "more" can make a dish better and give it more personality.  Univibe is a bit like lemongrass or cardamom or saffron, where you want this hint in the background but nothing too strong.

[Storing!]

Hmm that's a nice comparison Mark. I know Lime can distroy or make a dish.

I was planning to make the 2 extra stages switchable. Maybe just but I like options.
Besides that, I'm experimenting with the Tremulus Lune LFO for this build.
Still undecided... Hard choices if you don't know what will come out.

The added pic are 4 stages of Vibe. No end mix and amp yetr added Also no LFO present. (It's still on the braedboord). So I''ve got some room.

Wondering if I use the tremulus LFO what leds to use. Bright, Red, Green. etc... Any comment welcome



Guess the room will need to be filled with a fun application

[Mark Hammer]

I hear ya.

I put together a board with a pair of Ross/Ropez layouts on it because I too wanted phaser and Univibe in one.  One of the layouts is populated for phasing, and the other is populated for Univibe.  "Populated for Univibe" means not only different caps in the allpass stages but some slight differences in the LFO circuit (the usable speed range for Univibe is much narrower than that for phasing), and deletion of the regeneration components.  Naturally, both have vibrato dry-lift switches.

While there is much to be said for a "do-all convertible" unit, I think there is also much to be said for having multiple desynchronized modulation sources.  First off, the speed or speed adjustment range you want for each on its own is not always the same.  Second the filtering effects get more complex and richer with two units.  Third, highly periodic (now its higher, now its lower, now its higher, now its lower) modulation gets real boring real quick.  When you have multiple nonsynced modulation processes going on concurrently, it loses that periodicity and starts to feel a little more random and interesting.  I'm also planning to have a switch on mine to sync both units to a common LFO or allow each to use their individual LFO.  Again, sometimes a couple of unsynced sweeps is more interesting than a single sweep pattern but sometimes you want one monolithic sweep.  Since the cross-fed LFO remains operative whether the effect is bypassed or not, I can switch between phaser and Univibe, maintaining the identical speed.

Just a thought.

[Storing!]

IS the Univibe LFO that different? Maybe I should implement it then.
I picked the Termulus LFO for the tweakablity.
I don't have that much experience with LFO's. Just the regular Phase 90 and Alectric Mistress. So never gave it much thought.
As I understand the Uni's LFO is a special beast that gives it a unique flavor?

Maybe en Experiment with both on the breadboard will give an answer.

Thanks E

[Mark Hammer]

The "classic" Univibe's LFO was designed to work with an incandescent lamp.  The same  sweep feel CAN be achieved without that LFO or an incandescent lightbulb, but it has to be designed to achieve that feel.

Part of what takes place when a modulated effect like a phaser or Univibe or tremolo uses either a lamp, or photocells, or both, is that the responsiveness of one or both of those changes with speed.  If I was to say "Sit down and take your shoes off.  Okay, now put them back on again and stand up.", you'd be able to do the complete action.  If instead, I was saying "Put 'em on, take 'em off, put 'em on, take 'em off" quickly, chances are the shoes would never get taken fully off nor completely done up when put on.  That's what happens to LDRs and incandescent lamps when asked to change too fast.  That speed-related change is part of their character.

When I say two different LFOs in my previous posting, I'm actually talking about two identical LFOs but one of them omits the slow speeds that sound good with a phaser, and attains some slightly faster speeds.  That's simply a matter of changing a couple of component values.