Switch for Block or Script logo P90

[seibertdr]

Hi All,

I decided that I am going to mod my MXR P90. I see by a lot of threads that all you need to do is remove the R28 and you will get Script. I was thining of putting a switch in so I could get both. Does it matter which side of R28 I put the switch?

Thanks, Don

[ayayay!]

 Have you opened it up yet?  Make sure it's not all surface mounted stuff in there.  Many of the new Phase 90's are just the EVH phasers in an orange box. 

[seibertdr]

Not yet. I bought it used and it looks old. I will let you know tonight.

Also, what kind of switch would I use.

Thanks,

[bipedal]

Not sure if the R28 mod is all that's needed to convert a Phase 90 to "script" specs -- perhaps others can comment on that?

I used a spare SPDT switch I had laying around for my R28 mod: left one end of the resistor in place on the board, other end wired to middle pole of switch.  One of switch's end poles wired to pad that formerly had the other end of the resistor (so the switch is simply making/breaking the connection from resistor to board).  Shouldn't make any difference which end of resistor you use.

To my ears, the mod produces a rather subtle change; seems to give a little cleaner, smoother (less "bitey"?) tone to the phasing.  I generally play a Strat, so different guitars/humbucker pickups may produce a more noticeable distinction...

Good luck.

- Jay

[DougH]

First of all, "R28" is completely meaningless to anyone who doesn't have an MXR/Dunlop manufactured Phase 90 board in front of them. Many people build these for themselves from DIY-generated schematics and layouts. So I'm going to refer to "R28" as the "22k feedback resistor", since that's what it is anyway.

If you are familiar with a flanger that has a "feedback" or "regeneration" or "resonance" control, you know that turning that control "up" produces a more dramatic sound. Turning it "down" produces more of a subtle sound. Most of these control the amount of feedback in a feedback loop in the flanger. Generally speaking, more feedback produces a more "resonant" sound where it sounds like the harmonics get more exaggerated.

This is essentially what the 22k resistor does in a Phase 90. It provides a fixed amount  of feedback which tends to exaggerate the harmonics somewhat, producing a stronger and more "in your face" phase sound. Removing the resistor breaks the feedback loop and produces a more subtle phase sound. From my memory of what Phase 90's sounded like in the 70's I think this is the probably the most noticeable difference between a "script" and "non-script" Phase 90, although there may be others as well.

If you like both sounds, IMO the best way to implement a switch is to use another stompswitch to control this function. I don't like micro or mini toggle switches on stompboxes as they are just too easy to break. YMMV.

[ayayay!]

First of all, "R28" is completely meaningless to anyone who doesn't have an MXR/Dunlop manufactured Phase 90 board in front of them. Many people build these for themselves from DIY-generated schematics and layouts. So I'm going to refer to "R28" as the "22k feedback resistor", since that's what it is anyway.

Damn straight!

Anyway, when I did on my Phase 90 wayyyyy back when, I didn't notice much of a difference with the "R28 Mod."  I don't mean to disappoint you seibertrdr, but that mod is really overhyped.   If you want some real fun, do a search for some other mods on that pedal!  There's a couple cool ones that involve just removing a cap or two, or replacing a cap. 

The tough thing about adding the switch is that you really need a tiny one that isn't very deep.  There's not a whole lot of room to play with in those pedals unless you drill right into the battery compartment.  It can be done, but plan it well.   

[seibertdr]

Thank you all for your help and advice. I may think about this one a little more.

Don

[DougH]

Anyway, when I did on my Phase 90 wayyyyy back when, I didn't notice much of a difference with the "R28 Mod."  I don't mean to disappoint you seibertrdr, but that mod is really overhyped.

It's subtle, but I can definitely hear the difference. On slow speed the feedback loop gives it more of a "flangeresque" sound which is really noticeable with distortion. On faster speeds, the feedback loop gives it more of a "wah wah" sound instead of a "phase shift" sound IMO. I preferred it without the resistor/loop as I already have a flanger and with the harmonics less exaggerated it messed with the natural tone of my guitar less.

I have a couple sound clips of what my Phase 90 build (without the feedback loop) sounds like in my gallery: http://www.aronnelson.com/gallery/main.php/v/DougH/phaser/

This may give you an idea of what to expect if you remove the 22k resistor.