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DIY 12 stage phaser pedal

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With that many stages, I personally would go the optocoupler route myself (less noise inherent in the method).  Six VTL5C3/2's would get you there.

Having said that, if you want to go for a little-spoken-of-here route, why not go to 14 stages and try the ARP Quadra phase shifter that Juergen Haible adapted as a stand-alone unit?  Schematic, PCB trace and component overlay can be found here:

If you're unfamiliar with the sound of the Quadra phase shifter, think of the shimmery phase shifting of the synth instrumental in the middle of Styx's "Come Sail Away".

Cool thing about it is that it's a transistor ladder phase shifter, which you don't see every day (JH used CA3086 transistor array IC's for it, why he didn't go for CA3046's I dunno - maybe wouldn't make a big difference).  Being a transistor ladder, it should produce a fair amount of noise, but the Quadra had a very cool compandor setup to take care of that, and the compandor itself actually contributes a great deal to the sound of the thing.  Germanium diode clipping in the regeneration loop ...mmmmmm.

For detailed info on that awesome compandor, read up on his compandor notes for the Stormtide Flanger - he used the same thing in that.  JH loves the sound of it, and this is coming from a guy that's literally cloned nearly every high point of the of the analog world.  The Stormtide is linked on the same page as given above.


btw, Scott: did you follow zero the hero`s BadStone build-thread?  :wink:

Guess I must have missed that one, Ton.  Badstone - is that one six stages?

One day driving home from work I was wondering what in the world I'd do with all the cheap VTL5C2's I'd gotten from BGMicro.  It dawned on me that I could make a phase shifter out of them.  When I got home, I made a simple four stage phaser from the seat of my pants, and the thing actually worked, and sounded pretty good to boot.  Later I put an expo sink on it, which made it much better, and started adding stages.  I got to 10 before I got sidetracked.  

I found that once you get beyond six stages, the law of diminishing returns starts to kick in.  IE, six stages sounds quite different than four stages, but eight stages doesn't sound quite as different as six stages did in comparison to the jump from four to six.  Ten stages makes less of an aural difference when jumping from eight stages.  So, the more stages you go up, the more you have to add to make a big difference soundwise.  I think Mike Irwin explained the reasons for that quite well in a thread somewhere on this forum.   I imagine my next logical jump would have been to go to 14 stages.  The Tau Pipe had something like 20 stages, if I'm not mistaken.


Mark Hammer:
The Bad Stone uses a 4009 hex invertor chip as a set of six matched voltage-controlled resistors.  The ETI Phaser project, posted around somewhere, uses a 4049 like this also.  In one of his more capricious and ambitious moments, Mike made a 24-stager using a quartet of 4049s.  The demo I heard sounded magnificent, BUT:

- As anticipated, and as Mike mentioned to me and here as well, the noise was highly problematic and required a clever solution.

- The audible effect of having more stages CAN sound a bit more flanger-like but you need to have a wide-bandwidth signal to hear it.  The sample Mike provided me was done with a synth-derived broadband noise signal.  My guess is that 12 stages will sound fine but isn't going to sound all that "magnificent" if you plan on using it with an undistorted guitar.  The dramatic effect of flangers vs phasers is the increase in the number of audible notches as the delay time produced by a flanger increases.  Not only do the notches start lower down in the spectrum, but they also increase in number.  In the case of phasers, the number of notches produced remains constant, so the only way you're going to hear as dramatic an increase in number of notches when using a phaser is if the high end extends high enough that you could hear, for instance, the number of notches produced by a 12-stager go from 1 to 6 as it sweeps downward.  To do that, the 5 notches above that have to be so high that you can't hear them.  In other words, because you can't change their actual number, your only choice is to reduce their apparent number by having a wide-bandwidth audio signal and sweeping the phaser way up.

Scott's advice is probably appropriate, although I would say the advantage that extra stages buys you is a broader choice of where to tap and feed the regeneration signal.  In this spirit, Ross used a clever scheme for one of their FET-based phasers in which they used 5 stages.  Normally, because of phase relationships of a different sort, it is advisable to feed the regen signal through an ODD number of stages.  Typically, in 4-stagers like the P90, the last phase-shift stage is fed back to the input of the 2nd stage (i.e., the loop recirculates through stages 2, 3, and 4 - an odd number).  Ross added a 5th stage which was NOT swept, and sent the feedback signal through that, so that between stages 1-4, and the added stage, the recirclated signal went through 5 stages.

I mention this because you can apply the same logic to a 6-stager as well, adding a 7th unswept stage and sending the feedback signal all the way back to stage 1.  Or, if you felt like it, you could stick in a rotary or toggle switch and select where you feed it back to (e.g., stages 1, 3, or 5).

Finally, in the same spirit, take a peek at the MXR100, shown over at Generalguitargadgets.  This beast has 10 stages of phase shift, however only 6 of them are swept.  Remember that each stage produces a varying amount of phase shift across the spectrum (phase shift within each stage increases over frequency), and that the notches produced from the whole thing depend on the entire amount of phase shift produced across all stages.  So, if 4 unswept stages produce 33 degrees of phase shift each at some frequency X (132 degrees altogether), then the swept stages don't have to produce much additional phase shift at that frequency to generate a notch.

Scott, Mike, Ton, Steve, JC, et al:  One generally sees unswept stages having the same cap values.  What comments can you offer with respect to the possible effect of having additional unswept stages with staggered cap values, as in the Univibe or similar designs?  Is there anything to be gained in terms of the *perceived* sweep by distributing the fixed phase shift a little more evenly?


--- Quote from: britt-stinker ---I rerad that thing and It really doesn't say anything to me.
--- End quote ---

OK then, which bit did you first get stuck on? A phaser is not a simple thing to understand, but if you really want to get your head around it I'm (and no doubt others who've already posted on this thread) happy to help.

If on the other hand you're totally new to electronics and the GEO article really doesn't make any sense, you'd be best to start off with a simpler circuit - check:

The short of it is that each pair of phaser stages makes a notch using some clever electronics, and this notch is swept up and down by an LFO.  If you match the components closely in your pair, the notch will be deep and very noticeable.  If you don't match them at all then the notch will be shallow and hard to hear.

Stompbox quality phasers generally use multiple pairs of phaser stages with the notch in the same place.  They do not use matched parts as this is very time consuming.  By stacking the shallow notches on top of each other, they add up to a deeper notch.  So even though the MXR Phase 90 is a 4-stage phaser and the Phase 180 is a 6-stage (i think?), they are actually just simulating a well-matched two-stage phaser because they only have one notched frequency.

So your query about a 12-stage phaser has a simple answer and a complex one.  The Moog unit probably (I don't know) uses matched parts and is a 'proper' 12-stage phaser with 6 deep notches.  You *could* build a 12-stage MXR phaser by just adding a bunch of phase stages into the basic 4- or 6- stage design but it will just make a deeper and deeper notch and sound probably the same as a 6-stage.

If you would really like to build a DIY 12-stage phaser with 6 deep notches, let us know and one of us might design you one.  ;-)



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