Prophecysound Systems Pty Ltd
Pi-Phase mk2 user manual v1.3
pg. 2
PI-PHASE MK2 SLOW START, OR
–
‘S
O WHAT IS
PHASING EXACTLY?’
‘Phasing’ or ‘phase shifting’ involves creating animated notches at certain
frequencies by filtering the source signal, then mixing this processed signal
with the original (unprocessed) source signal. As with other phasers the Pi-
phase processes the audio signal using a series of all-pass filters, i.e. filters
that pass all frequencies BUT change the phase relationship of these
frequencies. By combining the phase-changed audio signal with the
original signal, cancellation of certain frequencies
–
and reinforcement
of others - occurs and hence produ
ces a number of ‘notches’. The
movement of these ‘notches’ is what
provides the characteristic phasing
sound.
WHY THE PI-PHASE?
The Pi-Phase mk2 is a reproduction of the Mu-Tron Bi-phase, a dual phase-
shifter invented and marketed by Musictronics USA in the 70s (*). It has
become well-known and well-loved for its 'classic' warm and deep sound,
as well as the flexibility of its control and audio-processing capabilities. The
Prophecysound Pi-Phase mk2 accurately reproduces the vibe of the
original unit. Design goals for the pedal were:
•
to match, as closely as possible, the sound of the original
•
to maintain a similar control layout
•
to package the pedal in a size and format that would allow it to
be used live
•
to dispense with the need for a special controller pedal for
switching channels on/off, or for controlling pedal sweep
•
to create a pedal that incorporated true-bypass (which the
original did not)
The Pi-Phase mk2 is all-analog and parts-accurate to the original, as much
as is possible. To our ears, and the ears of many previous customers, the
Pi-Phase mk2 sounds like the real-deal. How much like it? Original Bi-
Phases are pretty old, and some units suffer from parts drift, lack of
maintenance, and lack of calibration; each 'well-gigged' Bi-Phase can easily
sound different to the next. With your Pi-Phase mk2 we give you 'factory
fresh' dual-phaser experience.
The original control layout has been condensed to fit the targeted pedal
format, while still providing a clear and understandable way of operating
the pedal. The original architecture of the dual LFOs / dual phase shifters
has accurately been retained. The resultant format - a pedal 50mm (2")
high, 122mm (4.8") deep and 188mm (7.4") wide - can readily be
accommodated on most pedal-boards.
No special extra foot-switch is necessary to operate your Pi-Phase mk2;
true-bypass foot-switching for each individual phase channel is built into
the pedal. An external 'standard' expression pedal can be connected to the
rear CV input socket for control of the LFO speeds and / or manual sweep
of the phase sections.
* IMPORTANT NOTE! Prophecysound Systems claims no association with or
endorsement from Mu-Tron / Musitronics or the original designers of the
Bi-Phase.
CONTROLS AND OPERATION
Let’s run through the controls and functionality of your Pi
-Phase mk2.
Note that the text style [ITEM
] is used to denote when we’re discussing a
control, input to or output from the Pi-Phase.
The Pi-Phase mk2 consists of two LFOs (Low Frequency Oscillators) or
‘Sweep Generators’, two separate phase sections, and controls for
determining both audio signal flow and how the LFOs interact with the
phasing sections. Each function section
–
SWEEP GENERATOR 1, SWEEP
GENERATOR 2, PHASOR A and PHASOR B - is separated by outlines to
clarify the association between related controls.
SWEEP GENERATOR 1 / GEN 1 has three controls:
[RATE]
–
continuously-adjustable control that determines that rate at
which GEN 1 oscillates; adjustable from approximately 1 cycle per 10
seconds to 18 cycles per second
[MAN/PED]
–
toggle switch that selects the source for controlling the
speed of GEN 1. In the ‘MAN’ position the speed of GEN 1 is determined by
the position of the [RATE] control, whereas in the ‘PED” position the speed
of GEN 1 is determined by the setting of an externally-connected
expression pedal or CV signal.
We’ll cover the use of an external pedal or
CV connection later on in more detail.
[SHAPE]
–
toggle switch that selects between sine-wave (smoothly varying)
or square-wave (varying from one extreme to the other) modulation.
SWEEP GENERATOR 2 / GEN 2 has two controls:
[RATE]
–
continuously-adjustable control that determines that rate at
which GEN 2 oscillates; adjustable from approximately 1 cycle per 10
seconds to 18 cycles per second
[SHAPE]
–
toggle switch that selects between sine-wave (smoothly varying)
or square-wave (varying from one extreme to the other) modulation.
PHASOR A has three controls:
[FEEDBACK]
–
continuously-adjustable control that, when turned up from
the minimum setting clockwise, progressively adds more feedback to the
phased audio signal. More feedback
more of a noticeable phasing
effect, less feedback
a more subtle phasing / vibrato sound.
[DEPTH]
–
continuously-adjustable control that determines the width of
the frequency range swept by the modulation source. The greater the
depth, the greater the frequency range that is swept, and the more
noticeable the phasing effect.
[GEN 1 / PED SWEEP]
–
toggle switch that selects between GEN 1 and an
external expression pedal as the modulation source. In the GEN 1 position
the phasing will be controlled by the GEN 1 sweep generator, whereas in
the PED position the phasing will be controlled by an externally-connected
expression pedal or CV signal; in this way an effect similar to operation of a
wah pedal can be achieved.
PHASOR B has five controls:
[FEEDBACK]
–
continuously-adjustable control that operates as per the
feedback control for Phasor A.
[DEPTH]
–
continuously-adjustable control that operates as per the depth
control for Phasor A.
[SWEEP]
–
three-way rotary switch that functions like the [MAN/PED]
switch of GEN 1, but that adds the possibility of selecting also from GEN 2
as a modulation source. If both PHASOR A and PHASOR B have selected
the same modulation source, then their sweeps will be time-synchronised.
[NORM / REV SYNC]
–
toggle switch allowing non-inversion or inversion of
the modulation source signal. For stereo phasing effects, where both
PHASOR A and PHASOR B are modulated by GEN 1, you will likely want to
place this switch in the REV position.
[PHASOR B INPUT]
–
three-way rotary switch used for selecting one of
three input signal options:
•
IN A
the input signal to both PHASOR B and PHASOR A is
the same, commonly selected for stereo use of the Pi-Phase.
•
OUT A
audio is passed through both PHASOR A and
PHASOR B in series; if you have a single instrument and
amplifier then you’ll probably use this
setting.
•
IN B
different input signals to be processed by PHASOR A
and PHASOR B independently (although possibly still sharing a
modulation source).
EXTERNAL EXPRESSION PEDAL / CV CONTROL
An expression pedal may be connected to the [CV PEDAL] socket at the
rear of your Pi-Phase mk2; the pot in the expression pedal should be
connected across the sleeve and ring terminals of a stereo cable, with the
wiper connected to the tip. We recommend an expression pedal that
incorporates a 10k linear pot (e.g. Boss EV-5, EV-7) for optimal
performance; other expression pedals will work, but the range and ‘feel’ of
the response you get from your Pi-Phase may not be completely satisfying.