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design — construction — sound

New Version

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
  • Switchable Sync-Mode (from Rev.6)
  • Width: 12 HP
  • Dimensions: 128,5 mm x 60,6 mm
  • Depth: 35mm
  • Current consumption: ≈70mA
  • Optionally available in banana version
The XR22 VCO FT with AM input provides direct amplitude control of the sine/trianglewave by an external signal. An audio signal as AM input will be ring modulated by the oscillator frequency.  When using a control voltage for AM, the sine/trianglewave’s amplitude level can be directly controlled therefore.

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The knob ‘Gain’ is adding a positive/negative DC voltage to the oscillator’s amplitude control – for shifting the modulation point, loudness control or muting (when the external input signal is 0). The ratio between the (modulated) oscillator output and an applied AM input can be mixed with the bypass knob.
The FSK (frequency shift keying) feature is allowing to switch between two different oscillator frequencies – by hand, by a logic signal or by the oscillator’s squarewave itself. These two frequencies are controllable by the two big-sized knobs and their respective fine-tuning knobs and frequency  CV inputs. If the oscillator’s squarewave output is switched directly to the FSK input, the result will be a separate controlling of the rising/falling edges of the sine/triangle signal and the duty-cycle of the squarewave by the knobs and/or CV.  Ramp and pulse waveforms can be generated or it may be used for advanced wave shaping.
For optical overview, there is a full-color LED visualising the XR22 VCO FT‘s sine/triangle output and a bicolor LED for indicating the FSK state.
Sync Mode (New from Rev.6): The socket in the lower right corner is now offering double functionality: Either it is working as a F2-1V/oct. CV input or as a Sync logic input (replacing the CV input), depending on the state of the new switch ‘Sync ↔ F2 CV 1V/Oct.’.

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  • XR22 VCO FT panel drawing

    Panel drawing

  • XR22 VCO FT side view right I

    Side view right I

  • XR22 VCO FT side view right II

    Side view right II

  • XR22 VCO FT side view right 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 view

    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

Sync Mode: 1. Cymbal with pickup ⇒ Peak+Hold ⇒ XR22VCOFT AMin; 2. Rhythm machine ⇒ Peak+Hold ⇒ Delay1022 frequency CV modulated with synced XR22VCOFT triangle; 3. Sync mode in audio range; 2 XR22VCO FTs with sequencer F CV in; 1stVCO is syncing the 2nd

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

About Sync-Mode

With switch ‘Sync ↔ F2 CV 1V/Oct.’ in upper direction: ‘Sync’; socket ‘Sync/F2 CV 1V/Oct.’ (on lower right corner) will become a logic signal input (for trigger/gate/squarewave or similar). A positive going edge signal from 0V→+5V (min.) is resetting the oscillator:
With knob ‘Gain’ in cw position or a positive AM-CV, the  sine/trianglewave oscillation will restart at its positive peak.
Sync Mode positive Gain
With knob ‘Gain’ in ccw position or a negative AM-CV, the sine/trianglewave oscillation will restart at its negative peak.
Sync Mode negative Gain