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Eurorack Module


VCO with Ring Modulation Input and FSK (Frequency Shift Keying)

The ring modulator VCO XR22 VCO FT with AM-input allows direct ring modulation of audio signals with the oscillator’s sine/triangle signal. Alternatively, this input can be used to control the amplitude of the sine/triangle output (e.g. in combination with an envelope generator).
Further, the FSK (frequency shift keying) option with its two switchable different oscillator frequencies – controllable by the two big-sized knobs (and their respective fine-tuning knobs and frequency-CV inputs) – allows advanced waveform generation. The oscillator’s squarewave output can be switched directly to the FSK input, resulting in separate controlling of the rising/falling edges of the sine/triangle signal and the duty-cycle of the square output (for generating ramp and pulse waveforms) by the knobs and CV.
The new version – with another arrangement of the control elements on the panel – has now also a full-color LED for better visual control of the XR22 VCO FT ’s sine/triangle output.
The XR22 VCO FT is an improved version of the older XR22 VCO with a different manual frequency control.


XR22 VCO FT front view

Minijack Version
  • Amplitude Modulation (AM) Input
    • Ring modulation
    • CV controllable sine/triangle volume
    • Advanced waveform generation by AM
    • Rgb-LED for optical control
  • FSK (Frequency Shift Keying)
    • Pulse and ramp generation
    • Switching between two different frequency CVs
    • Advanced waveform generation by FSK
  • LFO-, Bass-, High- Mode
  • Optionally with Minijack or Banana Sockets
  • Width: 12 HP
  • Dimensions: 128,5 mm x 60,6 mm
  • Depth: 35mm
  • Current consumption: ≈70mA


AM In: Rhythm Machine; Output: Sine/Triangle – Oscillator frequency manually controlled

AM In: Rhythm Machine; Output: Sine/Triangle – Frequency CVs in: Sequencer and LFO

AM In: Rhythm Machine; Output: Triangle with FSK (Ramp) – F2 CVin: LFO

2 XR22 VCOs cross-patched FSK In ⇔Square Out – AM In: Rhythm machine; Frequency CVs in: Sequencer

Low frequency modeF CVin: Envelope Generator; 1.AM in: KorgMS20 VCO; 2. Frequency modulation of KorgMS20 VCO with XR22 triangle out

Or listen on


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XR22 VCO FT Drawing

XR22 VCO FT left side view

Side view left
XR22 VCO FT side view right

Side view right
XR22 VCO FT previous version

Previous Version
XR22 VCO waveforms


YouTube video


AM (Amplitude Modulation)

The triangle/sinewave output amplitude varies linearly with the control voltage applied to „AM in“. The modulation amount can be adjusted with knob ‚AM In‘. Negative CV’s will cause phase inversion of the triangle/sinewave output.


ringmodulation envelope am-feedback
Ring modulation with external triangle signal VCO volume control with external envelope signal AM in connected to triangle/sinewave output (feedback)

About FSK (Frequency Shift Keying)

The frequency of the XR22 VCO is controlled by two independent control sections F1 and F2 with their each independent manual frequency controls and CV inputs; either one or the other of these routes can be selected by a logic signal applied on socket „FSKin“ and/or by switch „FSK“.
a) Depending on the logic state of FSK control , either only F1 (with knobs  „F1“ and CVins „F1“) or only F2 (with knobs „F2“ and CVins „F2“) is active
b) In the low position of switch „FSK“ the FSK input is connected to the VCO’s own squarewave output and the oscillator frequency-shifts itself.
Now the oscillator produces ramp or sawtooth waves on its sine/triangle output and pulse waves on its squarewave output.
Rising and falling edges of the ramp wave and pulse/pause times of the squarewave can be independentlyand separately with knobs F1 and F2 and/or by their respective CV inputs.
c) By applying an external logic signal on input „FSK in“ (with switch „FSK“ in the middle position) the oscillator switches between F1 and F2

About Switch „Σcom→CVF2“

With this switch in upper position, both frequency control routes F1 and F2 (with their frequency knobs and CVins) are complete independently.
With the switch „Σcom→CVF2“ in lower position, now knob „F1/com“ and sockets „CVin F1/com“ and „F1/com 1V/oct.“ are working for both routes F1 and F2 – the ratio between F1 and F2 remains the same (but can be further varied by adjusting F2). An applied control voltage to the respective CV inputs „CV1/com“ and/or „F1/com 1V/oct.“ is now controlling both frequency routes F1 and F2; ensuring 1V/oct tracking when using both frequency channels similar (e.g. in FSK mode).