MXR Phase 90 Mods Help

[vanhansen]

I've searched through the archives for some mods I can do on my MXR Phase 90 and found the "script" or "R28" mod.  Seems simple enough.  

How can I wire a switch to go between the two modes (vintage and current)?  I'm assuming I just clip a leg of the resistor from the board, run a wire from it to the switch and then another wire from the switch to where the leg was clipped from the board.  Am I correct?  Would this work with a SPST toggle?

I also would like to make it true-bypass with a 3PDT switch but I don't know how that would be done on the Phase 90.

Any help/pics/diagrams is greatly appreciated.  Thanks.

[Fret Wire]

Do you have the reissue or a real MXR? Big difference in working on them. The reissues have pcb mounted switch, jacks, and pot.

[vanhansen]

It's a reissue.  My wife got it for me a few years ago to replace the other reissue I had sold a few years earlier.  I wish I had an original instead but ya know.

[vanhansen]

Ok, so I went to take a look at the curcuit board of my Phase 90.  Yep, everything is soldered to the board all right.  However, I cannot locate R28.  I can see labels for the transistors and a few of the caps and R30, which looks to be the trim pot, but where is R28 located?

[Fret Wire]

As you're looking down on the ckt board (switch at  bottom), R28 is right above the output jack.

[vanhansen]

Thanks.  I'll check that out.  I'm going to hold off on the true bypass, maybe I'll just build a true bypass looper instead.  Much easier and I don't want to risk messing up this pedal.

[Fret Wire]

Good move. Trying to true bypass the reissues rates right up there with being impaled by a telephone pole.

[vanhansen]

I removed the R28 resistor.  I like the change in the sound.  Much warmer and not as harsh.  That's what I've been looking for from it.  Thanks for the help and tips.

[ESPm2M]

Good move. Trying to true bypass the reissues rates right up there with being impaled by a telephone pole.

What would be the difficulty it true bypassing it? Couldn't you just de-solder and completely remove the onboard jacks and switch, and replace them with regular free standing Switchcraft jacks wired to a 3PDT and the PCB? Or is it a space issue (I haven't cracked mine open in a long time)?

[Fret Wire]

Also on the desolder list are the pot, led, and DC jack. Then you need to standoff the board, and the 3PDT still may not clear the board. Another method is to cut out a section of the board to clear the switch and leave the jacks and pot as is to retain the board.

Like I was saying, not too much fun.

[Khas Evets]

The R28 resistor creates a feedback loop, right? Is this what the button on the EVH model switches? If it is, that's an expensive switch. Has anyone tried using a pot instead of a switch? I would think having variable control of the feedback would be useful.