The Oakley Sound MOSPhaser is a six stage phaser (five
variable all pass filters and one fixed all pass filter) that
generates a classic sound. Partly based on a well loved 1970s
guitar effects pedal the MOSPhaser offers improved frequency
range, a more comprehensive modulation oscillator and external
voltage control.
Each
of the five all pass filter stages uses one of the MOSFET
transistors inside a CMOS invertor chip, the 4009UBE, to control
the centre frequency of the stage. By using a single integrated
circuit for all transistors means that no matching of devices is
required as would be the case if we were using discrete
components.
The
module is easy to build and requires only a simple voltmeter to
set up.
The unit includes a useful
internal low frequency oscillator (LFO) with accompanying
bicolour LED. The centre frequency of the phase shifter can also
be controlled by an external control voltage. This allows
envelope generators to be used to sweep the phaser to create
filter type effects.
Four front panel pots are
provided:
Frequency:
this controls the frequency of the two notches created by the
phase shift network.
Emphasis:
this accentuates the feedback signal within the phaser to create
a deeper effect.
Modulation: A
simple attenuator to adjust the level of the internal LFO or
incoming CV.
LFO rate: adjusts
the speed of the LFO.
The internal LFO produces a
triangle wave output, +/-5V, which is also available from a front
panel socket, LFO OUT. This allows you to use the MOSPhaser’s
internal LFO for other modulation purposes. The frequency range
of the LFO is designed for slow sweeps covering 7.5Hz to 0.01Hz (one
cycle every 70 seconds) although this can be changed by using a
different timing capacitor. The LFO signal is automatically
routed to the modulation depth pot when no jack is inserted into
the CV IN socket. The module features an on board jumper to
select whether the LFO OUT signal is inverted or non inverted
compared to the signal modulating the phaser circuitry.
The unit is designed to work
with standard MOTM/Oakley signal levels, although it could be
easily converted to be driven from other sources including an
electric guitar.
It is possible to purchase the
Sock4 circuit board which is available separately. This little
board speeds up the wiring of the four 1/4″ sockets and
reduces the chances of any wiring errors.
Power (+/-15V) is provided to
the board either by our standard Oakley 4-way header or
Synthesizers.com header. The board size is 143 mm (high) x 77mm (deep).
Current draw is around 35mA.
The MOSPhaser as a MOTM format module in a
natural finish Schaeffer panel.
Sound Samples
Pink Noise through the phaser
using the internal LFO. First half is with no emphasis and then
the emphasis increased during the second half returning to no
emphasis at the end.
Two Oakley VCOs set to
sawtooth and using the phaser’s internal LFO. The emphasis and
rate controls are manually altered during the sample. Some light
reverb is used for ambience.
Single sawtooth VCO used to
play a simple riff. The phaser’s frequency control is manually
adjusted.
Two VCOs, one sawtooth and the
other a triangle wave an octave below. The phaser is being swept
with a fairly fast envelope triggered on each note. The phaser
frequency is manually adjusted. No filter modules are used but a
simple delay is used to add interest.
The optional Sock4 socket board helps keep
the wiring to the sockets neat and tidy.
Downloads
Construction
Guide Our handy guide to building
Oakley DIY projects
Parts
Guide Our handy guide to buying
parts for Oakley DIY projects.
Schematics are only available
to purchasers of the PCB and will be sent via e-mail when the
board(s) are shipped.
Front Panel database
A Schaeffer front panel can be made for
this module. The database can be found by downloading the
following link:
5U format in
traditional black
To read these files you will need
a copy of ‘Frontplatten designer’ from Schaeffer. The program also features on-line ordering, so its
now even easier to buy your panels from Scheaffer.
The company are based in Berlin in Germany
and will send out panels to anywhere in the world. Delivery to
the UK normally takes around ten days. For North American users
you can also order your Schaeffer panels from Front
Panel Express.
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