Eurorack Module


VCO with Amplitude Modulation and FSK (Frequency Shift Keying)

The XR22 VCO FT  is a modified version of the XR22 VCO with a different manual frequency control.
Instead of the two ±2-octave switches and the two frequency knobs (ca 4-octave range), there are now two  frequency knobs (ca 7-octave range) for coarse tuning and 2 fine tuning knobs. Further, the ‚Low F‘ frequency range switch – which works for both FSK frequencies – is replaced by a 3-position shift switch with the settings ‚Lo‘ (for LFO/ tremolo applications), ‚Mid‘ (for bass sounds) and ‚Hi‘ (for normal/high frequency sounds).

XR22 VCO FT Minijack

 Minijack Version
XR22 VCO FT Banana

Banana Version
  • AM (Amplitude Modulation) Input
    • Ring modulation
    • CV controllable sine/triangle volume
    • Advanced waveform generation with feedback
  • FSK (Frequency Shift Keying)
    • Pulse and ramp generation
    • Switching between two different frequency CVs
    • Advanced waveform generating
  • LFO-, Bass-, High- Mode
  • Optional with Banana or 3,5mm Phone Sockets
  • Width: 12 HP
  • Dimensions:
    128,5 mm x 60,6 mm
  • Depth: 35mm
  • Current consumption:


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 mode F CVin: Envelope Generator
1.AM in: KorgMS20 VCO; 2. Frequency modulation of KorgMS20 VCO with XR22 triangle out

Or listen on


PDF Download


XR22 VCO FT Panel Drawing

XR22 VCO FT Banana left side

Banana Version left side
XR22 VCO FT Minijack right side view

Minijack version right side
XR22 VCO waveforms



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 generator 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 manual control „F1“ and CVins „F1“) or only F2 (with manual control „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 adjusted independently with knobs F1 and F2, the octave switches and/or by 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 also controlling both frequency routes F1 and F2; ensuring 1V/oct tracking when using both frequency channels (e.g. in FSK mode).