After over 43 years my Oracle turntable was in need of a refurbishing. The Papst motor was getting noisy and I was unable to fix the problem. A replacement motor was unavailable, so the next step was to replace the motor and motor controller. This entailed some electrical design and quite a bit of mechanical design and machining. The first attempt utilized a Maxon DC motor with an optical encoder feedback loop. Speed stability was fine, but the motor noise was unacceptable. Mitigation efforts were only partially successful.
The second approach used a DC brushless motor and a Maxon controller. Some motor cogging noise remained, but the addition of sound deadening polymer (Sorbathane) eliminated that noise. The controller speed is set by a DC voltage, so the auxilliary electronics are limited to generating the DC levels corresponsing to 33.3 and 45 RPM and producing a 60 Hz strobe signal to an LED. The latter makes it easy to calibrate the TT with a strobe disk.
Jeff
The second approach used a DC brushless motor and a Maxon controller. Some motor cogging noise remained, but the addition of sound deadening polymer (Sorbathane) eliminated that noise. The controller speed is set by a DC voltage, so the auxilliary electronics are limited to generating the DC levels corresponsing to 33.3 and 45 RPM and producing a 60 Hz strobe signal to an LED. The latter makes it easy to calibrate the TT with a strobe disk.
Jeff
