Years ago I observed that a turntable was a prime example of systems engineering, where the whole could be better or worse than the sum of its parts depending on how the trade-offs were managed. Here's the list I came up with of critical turntable functions:
A turntable and arm must:
• Provide a stable support for the record
• Rotate the record in the proper direction at a consistent and accurate speed
• Support the cartridge in the proper geometrical relationship to the record groove
• Allow the stylus to track the groove freely
• Provide consistent down-force at the stylus to maintain groove contact and preload the stylus suspension as specified by the cartridge manufacturer
• Compensate for any lateral forces generated by the cartridge support (e.g. skating force in a pivoted arm)
• Isolate the stylus from drive system noise and vibration, including bearing axial and radial runout that is perceived as rumble and noise generated by the drive motor and its speed-regulating system (pulleys, belts, idlers, servo circuits, etc.)
• Isolate the stylus from environmental noises including structure-borne and airborne vibrations
• Provide a reliable, low-noise electrical connection between the cartridge and the gain element that it drives (usually a preamp or an MC step-up transformer)
• Manage mechanical resonances in the system by moving them to frequencies where they will not impair the system's function or by applying appropriate levels of damping.
This is a tall order, and it explains why so few turntables and arms do an outstanding job of recovering the modulation from the record groove without adding or subtracting information. The designer of a turntable priced in the high five figures or more has plenty of latitude to solve all of these problems, and if he's lucky he can even amortize his development and tooling costs over his first year's production of ten or twelve units. The designer of a lower-cost turntable doesn't have the luxury of applying an expensive brute-force solution to each of these problems. His job is to make intelligent trade-offs, deciding which performance parameters are most important and allocating his limited budget to achieve good performance in those areas and performance that is at least acceptable in each of the other areas.
I went on to observe that too many modern affordable turntables mismanaged the trade-off by putting too little money into speed accuracy and consistency -- an observation that I still believe to be accurate.