We report on the far-infrared photoresponse of a quantum point contact device fabricated on a top-gated GaAs/AlGaAs heterostructure. The top-gated architecture avoids the disorder built into conventional modulation-doped structures. We observe a distinctive far-infrared magneto-photoresponse. This depends on the wavelength of the radiation and on the carrier density, which is controlled by the gate voltage. We conclude by comparison with transport data that the oscillations observed in photoconductivity and which are centred around the cyclotron energy arise from the resonant heating of electrons by the far-infrared radiation.