Mains – 50Hz. Whilst not probably relevant to run from mains nowadays (as everything has a PSU)…. Also tests run at 90V as I read somewhere that a more recent supply reduced voltage once the platter was spinning. All plots are captioned…. Z axis is the ‘stray flux’
Pure 50Hz. -80dB sine wave source and Apex PA93 high voltage amplifier. Using the recommended 0.22uF phase shift capacitor. This like a Valhalla but more refined as it is lower distortion and the amplifier is properly biased and does not have the crossover step.
Pure 50Hz sine wave drive to both phases with adjustable phase angle. The ‘null’ occurred with a 81.5 deg phase shift – 8.5 degrees off nominal… The harmonic spectrum is altered – reduced by 20dB at 100Hz but increased at 50Hz….
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and 90V
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And here are the absolute shaft speed measurements…. At 110V it looks like there is some saturation effect. 90V is cleaner BUT there is still a very large speed variation that occurs 24 times per revolution. Hardly a motor ‘designed’ for precision use in a turntable. OK for a heating valve or clock…. Does not significantly improve with precise phase tuning. In addition there is a tiny amount of stored inertia – 12gcm resulting at 250rpm in 0.4 milli Joules of energy.
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