MXR phase 90 problem

Discussion in 'The Projects Forum' started by babb27, Aug 10, 2011.

  1. babb27

    Thread Starter New Member

    Mar 16, 2011
    hey so my friend let me on his MXR phase 90 M101 pedal since it was broken. Initially the pedal would not turn on. So i found a shorted out Zener diode and replaced it. the diode broken upon taking it out so i couldn't tell what the rating on it was.

    now the pedal turns on, but only at the end (furthest clockwise) of the potentiometer does the effect turn on. the zener diode i replaced it with was a 5.7V 0.5W. i read somewhere that you match the zener diodes to the FET that is used. for the FET in the attached schematic they recommend a 4.7V. could this be the problem?

    any ideas or ways to troubleshoot would be appreciated.

  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
    I was reading HERE that the zener diode value needs to be "tweaked". They mention 5.1V.
    So you could just try out 5.1V and 4.7V and see how it goes.
    babb27 likes this.
  3. babb27

    Thread Starter New Member

    Mar 16, 2011
    sorry i meant to say it was 5.1V zener diode. thanks for the link i didn't even see the build reports down at the bottom of the page. those are very helpful.

    i read that people are using reverse log potentiometers to combat the problem with only having a noticable effect at minimum resistance.

    thanks for the link. and quick response. i will try some of the mods they suggest.