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  • Prophecysound Systems Pi-Phase Mk2

    By Phil O'Keefe |

    The return of the long-lost king of phasers



    Back in the 1970s a small yet innovative company called Musitronics built what many still consider to be the finest phase shifter ever built - the Mu-Tron Bi-Phase. It was a "pedal" in only the most liberal sense of the word, being very large and best-suited to stand or tabletop use; it also included satellite footswitches that attached to the main unit.


    In spite of its monster size, it had a sound and features that very few pedals before or since could even begin to rival. Unfortunately Musitronics / Mu-Tron was sold to ARP on a royalty basis in the late 1970s, ARP went out of business shortly after that, and in the years since the demise of Musitronics the prices for used Bi-Phase units have gone through the roof. Today you can easily drop two grand or more on one in decent shape - assuming you can find one. Fortunately, the good folks down under at Prophecysound Systems decided to take on the considerable challenge of trying to reverse engineer and bring this long-lost classic back. How did they do? Read on to find out.  



    What You Need To Know

    • The Pi-Phase Mk2 is a carefully researched and exceptionally well-built pedal designed to replicate the sound and features of the legendary Bi-Phase. The Pi-Phase, while smaller, has the same controls and a similar top panel layout as a Bi-Phase, making it easy to use for those who are familiar with the originals. The graphics separate each unit and its functions into different areas, so it's easy to tell what everything is and what it controls.


    • Housed in a much smaller, lighter, and more pedalboard-friendly unit than the original, the Pi-Phase measures approximately 2" H x 7.4" W x 4.8" D and weights about 1.65 pounds. The case is metal and painted white, and the top and rear panels feature cool blue, black and white Lexan panels. The high-contrast control labels are very easy to read.


    • Each phasor has its own individual 1/4" input and output jack mounted on the rear panel. As with the original, these are mounted "backwards" from what you'll find on most pedals today, with the inputs on the left and outputs on the right side of the pedal (when viewed from the player's perspective). This makes wiring the pedal into your board a bit trickier, but you'll most likely want to place it in a location on your board that allows for easy repatching whenever you want - that way, you retain more flexibility than if it was hardwired in such a way that repatching would be difficult without taking the whole board apart.
    • The rear panel also includes an optional external CV / expression pedal jack and power jack.



    • Like the original, the Pi-Phase combines two phase shifter units (named "Phasor A" and "Phasor B") into a single housing. Each Phasor has its own Feedback and Depth controls, as well as individual red LEDs to indicate when either one (or both) are active, and individual footswitches for turning each phasor on and off. Switching is true bypass.


    • The two Phasors have individual Sweep Generator controls. Phasor A's Sweep Generator has a control for setting the Rate of the LFO and phase sweep, as well as two toggle switches - one to select between Sine Wave or Square Wave modulation, and a second to select between the Rate control or an optional external CV / expression pedal for controlling the sweep.


    • Prophecysound Systems recommends using an expression pedal with a 10k linear pot. Examples include the Roland EV-5 and EV-7 as well as the Dunlop DV3 volume / expression pedal. I tested the review unit with a EV-5, and it worked perfectly.  


    • Phasor B's Sweep Generator also has the Rate control, as well as a Sine / Square Wave switch, but you have even more options - a dedicated knob can source Phasor B's sweep from Generator 1 or 2, or the optional external pedal. A Sync switch toggles between normal and reverse, so you can invert Phasor B's modulation relative to Phasor A, even when both are using the same sweep source.


    • That's not all! Phasor B has a dedicated Input control that selects among the rear panel Input A, Input B, or Phasor A's output. Yup - that means that the Pi-Phase can do phase shifting in parallel or series.


    • Internally, the construction quality is first-rate, and while you'll notice numerous trim pots inside, the manufacturer strongly cautions you not to go mucking around in there. Each pedal is carefully calibrated at the factory and it's easy to mess that up if you don't know exactly what you're doing.



    • No power supply is included, and battery power isn't an option, so you need to source your own supply. Prophecysound will help by providing information about exactly what you need, and may even be able to tell you who sells them in your area, but they decided not to provide power supplies since 1) they're heavy and would add to the cost of shipping the unit from Australia and 2) stocking them for a variety of countries really doesn't make tons of sense when people can obtrain them locally.


    • The Pi-Phase requires a 15V AC (not DC!) adapter that can supply a minimum of 500mA, equipped with a 2.1mm plug. In the USA, Analogman can assist you - just tell them you're looking for a supply for a Pi-Phase. 
    • Need some suggestions for settings to get you started? Recreations of the original's preset "cards" are included, as well as an extra one with an original Prophecysound Systems preset, and a couple of blank cards for saving your own favorite settings.





    • Unlike the originals, the included preset cards are not designed as "overlays" that can sit on the unit's top face. Still, their inclusion is yet another thoughtful touch.


    • As mentioned previously, the input and output jack configuration is "reversed" from what most pedals today use, with the input on the left and the outputs on the right. It's authentic, but not as patching-friendly.


    • People who wanted an exact clone may be somewhat disappointed by the unit's different physical size and slightly different layout. The more sensible among us will probably think they should get over it - go buy a vintage original if that's the only thing that will satisfy you. For the rest of us, this unit is far more useable and practical than the original, especially if you want to use it live, or put it on your pedalboard.



    How does it sound? In a word, glorious! And in stereo, it's almost indescribably good. Of course you don't have to run it in stereo to dig what this pedal has to offer; series phase shifting is cool too, and there's considerable flexibility you may not fully grasp until you try the various options for yourself. Want to process two different signals at once? Want two phasers with different settings for your dual-amp stereo rig? Dig super-slow phasing? No problem, as well as lots of other cool single phaser sounds and mesmerizing dual phaser combinations. Need a killer phaser for your studio? The Bi-Phase has been a studio favorite for years, and the Pi-Phase is every bit as effective. Check out the sound clips below for just a few examples of what this beast can do. Between this and their other highly regarded phase shifter (the Prophecysound Systems Infinitphase MkII), Prophecysound Systems are definitely in the running for the title of reigning phase shifting champs.


    While the Pi-Phase isn't an original design or concept, it's an extremely well-researched and superbly executed take on a true and long-discontinued classic. Does it sound exactly like a vintage Bi-Phase? It's close enough that I seriously doubt you'd be able to consistently and accurately tell the difference between the two in a side by side double-blind listening test. While it's smaller than a Bi-Phase, nothing feels cramped and it's a very easy pedal to use in spite of the wealth of possibilities.


    It's also cool that the footswitches are built-in and you don't have to worry about connecting (or losing) a separate footswitch unit. And for expressive control, the ability to use currently-manufactured expression pedals that are widely available is another plus. Best of all, compared to the cost of a Bi-Phase, the Pi-Phase is a bargain, and far more affordable. If you're a guitarist, keyboardist, or studio owner into the sound of phasing, give this pedal a try. If you're like me, you may decide it's just about the coolest phase shifter still being manufactured today. I did. I'll be purchasing one at my first opportunity for my own guitar rig, and for use in the studio.



    Prophecysound Systems Pi-Phase Mk2 (599 AUD ex GST, approximately $427.84 US dollars at the time of this writing, available direct from Prophecysound Systems - power supply and shipping are extra)

    Prophecysound Systems product web page


    To Purchase:

    Tone Factor




    Sound Samples:








    phil-3eaec998.jpg.272f8f73af02ca3efe8937c311f08503.jpgPhil O'Keefe is a multi-instrumentalist, recording engineer / producer and the Senior Editor of Harmony Central. He has engineered, produced and performed on countless recording sessions in a diverse range of styles, with artists such as Alien Ant Farm, Jules Day, Voodoo Glow Skulls, John McGill, Michael Knott and Alexa's Wish. He is a former featured monthly columnist for EQ magazine, and his articles and product reviews have also appeared in Keyboard, Electronic Musician and Guitar Player magazines.  

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    • Members

    One thing not mentioned in the review is the S/N Ratio.

    While sounding iconic, the original was really noisy.

    How does the Pi-Phase compare? Is it relatively quiet?


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    • Members

    The Pi-Phase is made from quality components and a first class PCB

    layout and as a result is very quiet. The best way to satisfy yourself

    of this is to visit Analog Man's shop where you can try one out.

    Otherwise if you can't do that, try listening to the sound bytes at the

    links Phil has provided above.

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