Hitachi HT-L70 turntable Lab Report

Lab Report

In common with the servo-driven, gimbal-suspended linear-tracking arm featured on the Technics SL-10 [HFN Apr '19], the 95mm (effective length) wand fitted to the HT-L70 also features an optoelectronic sensor to keep the lateral tracking error within a claimed ±0.1°. Movement in play is triggered by feedback from this 'contactless' optical system which must also cope with pressings of variable quality – spectrum analysis revealing the so-called 'bump/thump' as a momentary increase in the noise floor from ~10-40Hz [blue spectrum, Graph 2 below]. Its subjective impact will be influenced by the eccentricity of the record, and the LF music content, but it does not appear quite so obviously on the W&F spectrum [Graph 1, below] as it did with the SL-10.

Instead, while Hitachi's quartz-locked brushless/slotless/coreless DC motor brings the 296mm-diameter alloy platter up to 33.3rpm within 2-3secs (holding it to an absolute speed accuracy of –0.09%), the moderate 0.06% peak wow is dominated by ±3Hz sidebands. Any complex sidebands caused by the peak low frequency mode at ~13Hz [–60dB re. 1kHz/5cm/sec – blue trace, Graph 2] will likely be buried in the random/noise-like flutter shoulder of the main peak, this contributing to an aggregated peak-wtd flutter of 0.06%. Otherwise, the HT-L70's residual hum and noise is determined by both the proximity of Hitachi's electronics and susceptibility of the pick-up (an original MT-70 is fitted here), amounting to –78dBV, or –51.7dB relative to 1kHz/5cm/sec [black spectrum, Graph 2 below]. The through-groove rumble of –66.3dB (DIN-B wtd) is about average for the era but still a few dB shy of that achieved by the SL-10 with Technics' own DC motor. This motor also had the SL-10's platter up to speed about 1sec quicker... PM


Wow and flutter re. 3150Hz tone at 5cm/sec (plotted ±150Hz, 5Hz per minor division)


Unweighted rumble and hum over 0-500Hz range (black, arm lifted; blue, arm in silent groove)

Turntable speed error at 33.33rpm 33.30rpm (–0.095%)
Time to audible stabilisation 2-3sec
Peak Wow/Flutter 0.06% / 0.06%
Rumble (silent groove, DIN B wtd) –66.3dB
Rumble (silent groove, unwtd) –60.3dB
Hum & Noise (unwtd, rel. to 5cm/sec) –52.5dB
Power Consumption 8-10W
Dimensions (WHD) / Weight 315x83x315mm / 5kg