Michell Gyro turntable/arm Lab Report

Michell’s DC motor brings the Delrin platter up to speed within 4secs and, provided the bearing well is fully filled with oil, the deck’s speed is good to +0.05% [see Graph 1, below]. Thankfully, the low-rate drift seen with other DC solutions is avoided here, but the 0.06% peak-wtd wow sidebands coincide with the ±3.5Hz of the slightly stiffened main suspension. The Gyro’s treatment of noise is also atypical for while the direct, through-bearing noise is below average at –65.4dB (20Hz-20kHz, DIN-B wtd, re. 1kHz/5cm/sec) – visible between 20-30Hz and 65-95Hz on the magnitude spectrum – this improves significantly when measured through-the-groove at –73.7dB. Despite the felt washer being slightly too thick, adding the screw-down clamp couples the LP closely to the POM thermoplastic platter, boosting the S/N still further. With the clamp in place, the Gyro’s DIN-B wtd rumble is reduced to a state-of-the-art –75.6dB.

The partnering 9in TecnoArm 2 tonearm employs a Rega-sourced alloy tube with custom underslung counterweight – each graduation on the rear representing a ±0.1g change in downforce (accuracy is within 5%). The bearings combine zero play with a low <10mg stiction/friction while the holes drilled into the far 50% of the armtube [see p45] reduce the effective mass to 12g for improved compatibility with higher-compliance MCs and, especially, MMs. The tube’s main bending mode is an impressively high 205Hz but there is a far stronger, higher-Q 2nd harmonic (or other mode) at 535Hz along with sharp peaks at 1.5kHz, 2.2kHz and 3.1kHz [see CSD waterfall, Graph 2]. This is closer to the behaviour noted in the RB1000 [HFN Jun ’10] than in the ‘quieter’ RB2000 [HFN Aug ’15]. PM

ABOVE: Wow and flutter re. 3150Hz tone at 5cm/sec (plotted ±150Hz, 5Hz per minor division). Speed adjustment is not possible with the current PSU design

ABOVE: Cumulative resonant decay spectrum for the Michell TecnoArm 2 arm (100Hz-10kHz for 40msec). Note the short-lived, high-Q, midrange modes

Hi-Fi News Measured Specifications:

Turntable speed error at 33.33rpm33.35rpm (+0.05%)
Time to audible stabilisation4sec
Peak Wow/Flutter0.06% / 0.03%
Rumble (silent groove, DIN B wtd)–73.7dB / –75.6dB (with clamp)
Rumble (through bearing, DIN B wtd)–65.4dB
Hum & Noise (unwtd, rel. to 5cm/sec)–64.3dB
Power Consumption4W
Dimensions (WHD) / Weight495x180x385mm / 15.5kg
COMPANY INFO
J. A. Michell Engineering Ltd
Stevenage, UK
Supplied by: J. A. Michell Engineering Ltd
Telephone: 020 8953 0771
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