dca@iedl02.UUCP (02/14/84)
Generally, the determining factor in wether a turntable has pitch control or not is linked to wether it has quartz drive, not wether it has linear tracking. If a turntable has quartz drive then to have pitch control requires a completely separate RC based oscillator (which is also why those turntables which have the separate oscillator are less stable when switched off of the quartz reference). David Albrecht General Electric iedl02!dca
dmmartindale@watcgl.UUCP (Dave Martindale) (02/17/84)
It isn't necessarily that a turntable which uses a quartz oscillator for its frequency reference needs an RC oscillator for pitch control. Normally, the servo system will try to phase-lock the turntable's rotation to a reference frequency which is the quartz oscillator's frequency divided by an appropriate magic number. To get variable speed, you can either replace the quartz oscillator by an RC oscillator (cheap but not stable) or you can change the "magic number" that the reference oscillator is divided by. If the frequencies involved are chosen so that the "magic number" is large enough, then the frequency can be changed in increments smaller than what you could possibly set using an analog control while retaining the stability of the quartz oscillator.