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70's mxr phase 90 help needed!

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  • 70's mxr phase 90 help needed!

    hi guys

    i installed a dc jack on my old, 74ish, script logo phase 90. i seem to have done something wrong and the thing now sounds like a vibrato pedal. i.e.-i'm only hearing the modulated signal without the direct signal, hence no phase. my phase 90 already had true bypass (dpdt switch) and i've drilled a hole and installed a 3 dc plug like this Jack, DC Power, 2.1 mm All-Plastic, Round.

    i returned the wiring to stock (with the bypass mod) but it hasn't fixed the problem. does anyone have any idea what might be wrong?

    btw, please give me the dumb guy explanation/wiring drawing (no schematics please), i'm a guitarist y'know.


  • #2
    Difficult to answer under your terms.
    Juan Manuel Fahey


    • #3
      So you're saying that it produces a vibrato sound? (which is what you get when the dry signal is lifted from a phaser)


      • #4
        yes mark, that seems correct. a subtle, oscillating pitch shifting. the rate knob works, the signal passes through when off.


        • #5
          Well, given that both the phase-shifted and clean signal pass from the input buffer stage to the output mixer stage, and given that you have an audible phase-shifted signal, it would seem that the only discernible source of problem is that the clean signal isn't making it from the input buffer to the output mixer.


          • #6
            yeah, any idea where to look? a component to test? should i just send it to a tech?


            • #7
              Please do.
              Any other answer would imply a schematic.
              Juan Manuel Fahey


              • #8
                I have 98% certainty on this diagnosis. The thing worked, you did stuff and now it doesn't. Taking it apart and putting it together subjected it to mechanical stresses and I'll bet your problem is mechanical; broken solders, damaged component lead something like that. On the chance that it isn't, it will be related to some other activity, dropped solder blob, bridged joints, stray component lead or cutoff. These are the usual post-work issues. Not only for beginners but for even the most experienced pro. The difference is that the pro knows to look to his work first.
                My rants, products, services and incoherent babblings on my blog.