MXR Phase 90 Questions - Script?

[azrael]

What exactly makes the Script Phaser 90 "better" (subjective, of course...)?
I haven't found a definitive source on what the component differences are.


I was thinking of building one on the cool layout at Tonepad.com.

[solderman]

Well it's, as always, Your own opinion that decides what's "best" but the main issue that concerns people with the contemporary MXR phase 90 and the script version is that the new one seems to distort on mid notes. The script mod for the new version does not bring it back to the same circuit as the 70:s script. It just removes the 22K feedback resistor. Do remember to match your FET:s
You can find more about this here
http://www.pedalarea.com/comparisons.htm
And here
http://www.erikhansen.net/?page_id=31

[azrael]

I've seen the second link before, and while those mods do appear to improve the sound, I read this:

Please note before continuing that these mods will NOT turn your reissue in to a script logo version. They will however, help improve the sound of the circuit.

So what makes a vintage Script Phase 90 a vintage Script Phase 90?
I've seen a link with gutshots, and there's a bunch of different parts ("extra", even!). I just couldn't believe there wasn't any info on the exact differences.

[DougH]

I've never gotten a straight answer on this either. I've heard mojo BS about component quality etc, but no one has sat down and listed the differences in component types between "script" and "block" phasers that I've seen- or for circuit differences (beyond the 22k). In the end, leaving out the 22k feedback resistor is the biggest bang for the buck mod for getting the subtlety of the "script" phasers.

[azrael]

Yeah, and on another page on the same site with that mod, they list the difference in parts and the "extra" ones and show pics:
http://www.erikhansen.net/?page_id=32
But don't specify where they go in the circuit/schematic or what they do.

BTW, DougH, I built your Hot Silicon, sounds great! Currently my main fuzz.

[DougH]

Haven't looked at the site you're linking, but IME most "mod" sites do a piss-poor job of explaining "why" something does what it does. Most of it is written from an "insert tab A into slot B" mentality, and in all honesty, from an electronics perspective I don't think most of these people really understand what they are doing anyway. It's mostly Easter-egging from what I've seen. Furthermore, most of them don't even put up before/after schematics so it's a PITA for someone who does know what they are doing to get a sense of what's really going on with the circuit, and why it sounds like it does.

[vanhansen]

Nice to see my site still gets looked at.  I put that Phase 90 info up nearly 5 years ago.  The page that does the part comparisons is actually info that was posted in a thread right here on this forum.  I thought it was neat to see that so with the permission of the author, I posted it on the site.  

It's been quite a while since I've done any mods or building.  I need to get back in to it when I have time.

A vintage script Phase 90 has less parts, obviously, and a less subtle and smoother phase to it.  The modern Phase 90's are more in your face and sound more harsh to me.  Removing R28 helps to smooth it out and make it a little more subtle.  My guess is that component values and tolerances will be all over the place due to using what is available at the time and "close enough to work". 

The kicker lately has been that Dunlop has been using SMT components on them so the location of R28 is not in the same spot on the board as the conventional component versions.  I haven't dug around in one to find out where it is exactly but I have owned an EVH Phase 90 and IMO, it is one of the best new phasers out there.  If you want pure vintage, go for the '74 Script Reissue.

[zombiwoof]

As others have said, the original script Phase 90 had a simpler circuit.  MXR (the original company) changed the circuit over the years, adding a feedback circuit that added more intensity and "swoosh" to the sound.  They also added LED's at some point.  These changes were in effect in the later block logo MXR pedals, although there were transition models that were closer to the script version.  When Dunlop took over making the MXR pedals, they at first made them exactly like the last version of the original pedals.  That is, they had the extra circuit changes but had the same board layout, and used case mounted jacks and switches.  I have one of these early Dunlop Phase 90's (as well as an early Dunlop DynaComp).  As time went by, Dunlop first changed the board so that the switch and jacks were mounted to the board.  Then, they started using surface mounted components which make it even hard to mod the pedals.  The point is, these pedals went through many revisions, during the original company's period of manufacture, and later after Dunlop started making the pedals.  So, you can't blame Dunlop for the added circuit changes that made the pedal more intense, that was actually done during the original company's era.  They can be blamed for the surface mount components, which make the newer pedals harder to mod.  I do applaud them for reissuing the '74 vintage model Phase '90, which went back to the original design.  I wish they would make a vintage Distortion+ next.

Al

[aennekin]

I think this video comparison of a 75 Script Phase 90, a 77 Block "Transition" Phase 90 and a Dunlop 74' Handwired Reissue is pretty interesting. It seems that the only real difference between the handwired reissue and the Script original is the use of metal caps in the new as opposed to carbon caps in the old.

Which has me wondering, has anyone thought to take the new handwired reissue and change out the metal caps to make it sound more like the original? It sounds much closer to the original (and better) than the early Block logo model but I wonder if it couldn't be made to sound even closer by switching the caps out?

[aennekin]

Oops, forgot the link. My apologies!

http://www.youtube.com/watch?v=NjBJRjf-cHc&feature=player_embedded

[Mark Hammer]

The role of resonance in effect sound was something not discussed much about MXR products at the time.  I bought an Envelope Filter shortly after they came out, sold it when I had to move provinces, and then bought another one some6 or 7 years later.  I found some differences in component value, and only years later did I learn that the value change had  the impact of increasing resonance/emphasis, and making a more intense filtering sound.  It would seem that the same course of events befell the P90; first starting out with lono resonance/feedback, and then changing to the addition of fixed-amount resonance.

[DougH]

Re. the video-

The "transition" one and the bud box one both had more midrange than the reissue. However the bud box one had more resonance due to the 22k feedback resistor. You could hear it sounding more "wahwahlike" at the 2:00 position. But I think these kinds of tests are kind of useless unless he makes sure the trimpot settings are matched. Even that might be kind of useless without knowing the characteristics of the FETs used in ea model.

IMO, the presence/absence of the 22k (feedback loop) still makes the biggest difference in the sound. The rest is much ado about nothing. There are other differences, but they are pretty trivial and IMO cannot be characterized as "good" or "bad"- just "different".

[solderman]

I just recently made a layout of the Phase 90 to fit in a 1590A box using the schematic at Tonepad. Before I did the layout I went over the circuit to see if I wanted to modify it some how. There is actually not that much to tamper with in there. It's a pretty strait forward circuit. The only modification I made was to replace the 22K feedback resistor wit a 500K trim pot. If you take a look at the MXR phase 90 schematics and use the Tonepad one as reference there are a couple of things in there that can make a difference sound vice.

1. First and most obvious is the 22K feed back resistor. The rest of the audio path going trough the phase shifting block of the circuit have no obvious component that will alter the sound in a positive way. What FET:s where used do not matter since they do not inflict on the sound them selves. The same goes for the IC1b and its surrounding components that make up the LFO and therefore only interesting when it comes to sweep symmetry and characteristics and speed. Not sound.

2. Matching of the FET:s does change the sound. There is absolutely no way of knowing how accurate the FET matching was on different builds trough out the years. This can alter the sound a lot. Specially on slow settings.

3. Change in the 10K/10nF at IN will alter the frequency that will be passed trough.

4. Change in the 150K/150K mixing resistors at the base of the Q5 will alter the balance of wet and dry signal.

5. Changing the 56k/50nF/150K at the Q5 collector at OUT will also change the frequency passed trough.

6. The 1M can alter the depth modestly

[DougH]

Those are good points. Another thing to think about if you are building one is adjusting the output level. I tweaked that a little hotter on mine, since it sounded slightly less than unity gain.

[azrael]

Never checked this thread for some reason.

Good info here, though!