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Product ID: PDO MKII

WMD Phase Displacement Oscillator (PDO) mkII



The mkii version of the pdo is available: better cv handling, 16 hp, single pcb instead of stacked boards. an upgrade path is available for those with mki versions, contact wmd for more information.

Introducing the wmd phase displacement oscillator (pdo). this hybrid vco has all the feel of an analog vco but with the benefits of digital waveshaping. the pdo will easily find a home in your system!

The PDO exists to utilize the phenomenon of phase modulation (pm). this allows for the relative phase difference of its outputs to be set or modulated, producing very interesting sounds. the result is similar to frequency modulation (fm) but affects the output to a greater degree without affecting the stability of the initial frequency.

PM has the same benefits of quadrature filters/sine wave generators and greatly exceeds their capabilities at audio rate modulations. pm is highly useful for for creating metallic and bell tones and very controlled harmonic interactions.

Because PM affects the relative phase and not the frequency of the waveform generated, the pdo can self modulate its pm inputs. thils creates complex harmonic signals that seem to vary in frequency but are quite stable.

Phase modulation is also quite powerful when using the pdo as an lfo. adjusting the relative phase of each output allows for very precise modulation of other modules. each output can have any of the available waveforms simultaniously. there is a myriad of modulation possible with the pdo!


  • Analog sawcore vco
  • Temperature compensated
  • Linear or expo fm
  • Calibrated 1v/oct input
  • Hard sync input (lfo reset)
  • ~.0012hz (14min) to >=10khz
  • Digital waveshaper
  • Four separate waveform outputs
  • Phase modulation for outputs 2,3,4
  • Global phase input
  • Invertible cv inputs for phase mod
  • Any waveform on any output
  • 14 bit input, 12 bit output
  • 100khz sample rate
  • Channel indicator leds
  • Sum output of all channels
  • Normaled sum output
  • Expandable
  • Expand/jack cv simultaneous
  • 16hp, +85ma -45ma power draw 

Controls and i/o

The PDO's analog vco should feel familiar and intuitive.

  • 1v/oct input - calibrated input for pitch control. the vco will track at least 5 octaves using this input.
  • Sync input - rising edge sawtooth reset/sync input. does not affect slope of sawtooth. use as lfo reset also.
  • Coarse & fine knobs - coarse knob adjust the frequency of the vco throughout its full range. use the fine knob to tune the oscillator within approximately 1/3 octave range.
  • FM - jack for frequency modulation. type is selectable with switch between exponential and linear. linear may be dc or ac coupled with a rear jumper.

Phase modulation inputs (Φ):

Phase inputs (fcv) - the pdo has three phase inputs, one for each channel: 2, 3 and 4. these inputs can use any type of signal. each phase input has a bipolar attenuator, turned cw past center for positive modulation, turned ccw past center for inverse modulation.

  • Phase offset (Φ) - these controls set the relative phase of each channel, from 0 degrees to + or - 360 degrees. this control is added to the fcv input and acts as a bias level control when there is an input.
  • Global phase input (fcv234) - this jack sends its signal to each phase input equally, allowing for a single signal to globally control the phase offset of each channel.
  • Jack / both / mod switch - this switch controls routing of the cv signals for interfacing with the triple bipolar vca. jack allows the front panel jack and attenuator through. mod allows just the input from the tbvca through. both sums both signals going into the phase modulation circuitry.
  • Inv switch - this is the master invert switch for the sum of the jack/mod/both and the global phase input per channel. it will invert all signals.


  • Out1 - out4 - these are the outputs for each channel, the current level is displayed at the top of the module by a green led.
  • Sum output - this output takes all four of the outputs and sums them together. out2 and out3 are always summed to this output. out1 and out4 are normaled through the jack. so plugging into out1 or out4 will remove that signal from the sum output.
  • Staircase output (sc out) - this output jack is the result of the relative phases of the three phase input channels compared to the analog sawtooth waveform. it forms a Staircase type output (multiple square waves added together).
  • Sum normaled output - this output takes each output (1-4) that do not have cables inserted and sums them together. use this if you want to remove an output from the sum


There are two expansions for the pdo.

  • Quad anti aliasing filter - this 4hp expansion module consists of four independent -24db/octave butterworth low pass filters. they all share a common frequency input and bias knob. the quadaaf independently filters each output from the pdo, providing an anti-aliased (smoother) output. there is also a sum output of all four filtered signals.
  • Triple bipolar vca - this 8 hp expansion module contains three independent polarizing vcas. this allows for mod mode to be used which will produce stable wavefolding without patching. by applying envelopes and other signals, very dynamic patches can be produced.

Other notable things:

  • The phase displacement oscillator is 16hp.
  • Current consumption is 85ma for the +12 rail; 45ma for the -12 rail.
  • The depth from the back of the panel is roughly 26mm


Additional Information

Warranty: 1 year
Module Format Eurorack
Function(s) LFO, Oscillator, Phase Shifter
Width (HP) 10
Sort by: DESC
Great VCO! Review by Wut
This is a very nice and unque sounding module. Its great for drones and agressive basslines. Make sure you have enough VCAs around, or the dedicated expander (TBVCA). The module occasionally sounds somewhat lo-fi, but it can be interesting in that regard too: unique glitchy sounds can be found in the high end of the frequency range. (Posted on 17 June 2015)
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