A magnetic field gradient generating system for a NMR system, includes at least one set of gradient coils, preferably arranged according to three axes of a spatial referential system, and a controlled power supplying unit for the gradient coils, the power supplying unit including, for each gradient coil, a converter/amplifier module, the modules being fed with pulse sequences of digital gradient data provided as word streams by an adapted gradient data generator according to a pulse program, each arrangement of a gradient coil and a converter/amplifier module forming a gradient channel. The power supplying unit also includes an automatic blanking system which scans the gradient data words sent to the [converter/amplifier] modules and, according to sensed values, selectively delivers blanking signals to be applied to the modules in order to disable the power stages of their respective amplifiers connected to the gradient coils, when no current is to be fed to the coils.