Phoenix Engineering
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- Jun 2, 2023
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Just read the Stereophile review; like the previous review of the HW40, most of the important stuff came from the mfr rather than from independent analysis. VPI hasn't corrected their previous errors/exaggerations i.e. the torque of the motor being 2.68 Nm/s (the units are Nm not Nm/s). 2.68Nm is the peak output the motor is capable of for 1 second max and requires something like 40A at 12V to achieve it. The HW40 was capable of .74Nm at start up (limited by the 50W power supply and in software), but produced ca. 6.8 mNm during normal operation according to the controller software, which is very similar to a number of modern belt drives. Still not sure why you would use a 500W motor on a turntable when normal running operation only requires ~30mW?
Interesting that they changed controllers; the Stereophile review mentioned a TI controller using 3 phase sinewave drive but the HW40 used an off the shelf industrial controller made by Elmo Motion Control (Gold Solo Twitter) and block commutation which produces cogging. They are using the same magnetic ring encoder for speed feedback with 2560 pulses per rev (they report anywhere from 2400 to 2500 PPR) but in reality, the actual encoder ring only produces 80PPR and the read head synthesizes the higher number. It's an odd choice because the HW40 controller took a reading once per second and could only work with integer numbers and the math doesn't quite work out in their favor (at 33.333 RPM it takes 1.8S/rev so 2560/1.8=1422.222 counts/sec). The controller software would report nearly constant speed errors as it bounced back and forth between 1422 and 1423 counts. The speed as measured at the platter also changed between 33.328 (1422 counts) and 33.351 (1423 counts) as measured by a RoadRunner tach (accurate to 1.5PPM or better). Hopefully, the TI controller produces better results.
Does anyone know if they used the TI controller in the later version of the HW40? That might explain the price increase from $15K to $22K and the sudden departure of their engineer Michael Bettinger who did some design work on the HW40. I wonder if there is an upgrade path for the early adopters of the HW40?
Interesting that they changed controllers; the Stereophile review mentioned a TI controller using 3 phase sinewave drive but the HW40 used an off the shelf industrial controller made by Elmo Motion Control (Gold Solo Twitter) and block commutation which produces cogging. They are using the same magnetic ring encoder for speed feedback with 2560 pulses per rev (they report anywhere from 2400 to 2500 PPR) but in reality, the actual encoder ring only produces 80PPR and the read head synthesizes the higher number. It's an odd choice because the HW40 controller took a reading once per second and could only work with integer numbers and the math doesn't quite work out in their favor (at 33.333 RPM it takes 1.8S/rev so 2560/1.8=1422.222 counts/sec). The controller software would report nearly constant speed errors as it bounced back and forth between 1422 and 1423 counts. The speed as measured at the platter also changed between 33.328 (1422 counts) and 33.351 (1423 counts) as measured by a RoadRunner tach (accurate to 1.5PPM or better). Hopefully, the TI controller produces better results.
Does anyone know if they used the TI controller in the later version of the HW40? That might explain the price increase from $15K to $22K and the sudden departure of their engineer Michael Bettinger who did some design work on the HW40. I wonder if there is an upgrade path for the early adopters of the HW40?