Dgarretson,
Albeit the fact you are running a rather complex idler system on your drive chain, I still agree with Doug that you'll have audible cogging via the Mylar belt, especially with the 300 RPM motor. I've tried implementing the same Hurst motor (with the Kelly AC-1) in a "direct" pulley to platter setup on my Galibier, and have a hard time with the cogging artifacts, especially at 33RPM (the cogging is much less audible at 45 RPM). And yes, the Mylar belt will provide a much more direct link to the drive mechanism than string - too lossless for the Hurst AC motor. The Hurst motor in question simply has too much torque to allow for smooth rotation - so much so that I've been seeking alternative motors with less torque to try this experiment again - the Premotec/Philips-Airpax (as used in the Linn) with 4 mNm torque, and the Berger-Lahr as used in the Raven AC with 7 mNm of torque seem like better, low cogging alternatives to the Hurst with its beefy 19.06 mNm of torque. I now understand why VPI uses all those rubber belts, pulleys and flywheels - they are absolutely necessary to reduce the audible cogging of the Hurst motor. That said, I think there is some degree of virtue to be had with an AC synchronous motor - qualities that I am not (at this time) ready to remark upon fully, as more experimentation is needed. However, the Hurst is a fine 300RPM motor - very stable and with enough torque to overcome all but the mightiest amounts of stylus drag; I can see why VPI uses this motor. I'd also like to comment very positively on Mr. Kelly's controller - I wish I had one when I still owned my Linn; in many ways, it is far superior to the Lingo, if only for the fact that it can be tailored to the needs of every motor (of which no two are exactly alike). Good listening,
-Richard
Albeit the fact you are running a rather complex idler system on your drive chain, I still agree with Doug that you'll have audible cogging via the Mylar belt, especially with the 300 RPM motor. I've tried implementing the same Hurst motor (with the Kelly AC-1) in a "direct" pulley to platter setup on my Galibier, and have a hard time with the cogging artifacts, especially at 33RPM (the cogging is much less audible at 45 RPM). And yes, the Mylar belt will provide a much more direct link to the drive mechanism than string - too lossless for the Hurst AC motor. The Hurst motor in question simply has too much torque to allow for smooth rotation - so much so that I've been seeking alternative motors with less torque to try this experiment again - the Premotec/Philips-Airpax (as used in the Linn) with 4 mNm torque, and the Berger-Lahr as used in the Raven AC with 7 mNm of torque seem like better, low cogging alternatives to the Hurst with its beefy 19.06 mNm of torque. I now understand why VPI uses all those rubber belts, pulleys and flywheels - they are absolutely necessary to reduce the audible cogging of the Hurst motor. That said, I think there is some degree of virtue to be had with an AC synchronous motor - qualities that I am not (at this time) ready to remark upon fully, as more experimentation is needed. However, the Hurst is a fine 300RPM motor - very stable and with enough torque to overcome all but the mightiest amounts of stylus drag; I can see why VPI uses this motor. I'd also like to comment very positively on Mr. Kelly's controller - I wish I had one when I still owned my Linn; in many ways, it is far superior to the Lingo, if only for the fact that it can be tailored to the needs of every motor (of which no two are exactly alike). Good listening,
-Richard