Synthesis Technology MOTM-485 GX-1 VCF (12dB Sallen-Key)


  • Freq
    controls the cutoff frequency
  • LP/HP
    cSelects the filter type
  • Res
    controls the resonance
  • Full/Half
    switchable half/full tracking of the 1V/Oct input
  • FM
    controls how much FM influences the filter cutoff frequency


  • 1V/Oct
    controls the cutoff frequency (-7V to +7V)
  • FM In
    controls the filter cutoff frequency (-7V to +7V)
  • Res
    controls the resonance (-7V to +7V)
  • In 1/2
    audio inputs (-5V to +5V)
  • Out
    audio output (-5V to +5V)


the Synthesis Technology catalogue

The MOTM-485 is a recreation of the Yamaha GX-1 LP/HP filter. The GX-1 was a massive organ/synth hybrid, costing over $60,000 in the late ‘70s. The best example is the ELP song ‘Pirates', but was also used by Stevie Wonder and Led Zepplin.. The actual GX-1 used a pair of these filters to form a bandpass response (the same method used in the MS-20 and the CS-80). There is a HP filter set to "half tracking" followed by a LP at "full" tracking. However, you can still use a single MOTM-485 as yet another distinct tone in your setup.

  • Faithfully captures the unique GX-1 timbre
  • 2 audio inputs
  • voltage-controlled resonance
  • switchable HP/LP response
  • switchable half/full tracking of the 1V/Oct input
  • fully temperature compensated using TEMPCO resistor and matched pairs
  • not a ‘clean' filter: has higher distortion than other MOTM filters

The MOTM-485 does contain trims that can be adjusted with any DVM.

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