CG Products
design — construction — sound

Eurorack Module


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

XR22 VCO FT front view

Front view
  • 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
  • Width: 12 HP
  • Dimensions: 128,5 mm x 60,6 mm
  • Depth: 35mm
  • Current consumption: ≈70mA
  • Optionally in banana version available
The XR22 VCO FT with AM-input is allowing direct ring or amplitude modulation of an input with the oscillator’s sine/triangle signal. With an audio signal applied on the AM-input, the signal will be modulated by the oscillator frequency. The ringmodulated result is available on the triangle/sinewave output; it can be mixed with the original signal by a ratio knob. When using a CV as AM input, the sine/trianglewave’s amplitude can be directly controlled by the CV. Control knob ‘Gain’ is adding a positive/negative DC voltage to the oscillator’s amplitude modulation input – for shifting the modulation point, loudness control or muting (when the external input signal is 0).
The FSK (frequency shift keying) option makes it possible to switch between two different oscillator frequencies – by hand, with a logic signal or by the oscillator’s squarewave itself. The two frequencies are 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.
There is a full-color LED for visual control of the XR22 VCO FT ‘s sine/triangle output and a ‘FSK’ LED for indicating the FSK state.
  • XR22 VCO FT panel drawing

    Panel drawing

  • XR22 VCO FT right side view I

    Side view right I

  • XR22 VCO FT right side view II

    Side view right II

  • XR22 VCO FT right side view III

    Side view right III

  • XR22 VCO FT left side view I

    Side view left I

  • XR22 VCO FT left side view II

    Side view left II

  • XR22 VCO FT back side

    Back view

  • XR22 VCO FT banana version

    Banana version


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

About 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