So what about the motor control on the SL-1200? After all these years it's now configured for DJ use and has as much torque applied as it can, and that leads to the PLL being close to the edge of instability as you can see here
http://www.soundhifi.com/sl1200/index.htm (near the bottom of the page) . It's unlikely that the average person has intimate knowledge of feedback principles or PLL dynamics, and it's beyond this forum to teach it. You could just take my word as an ex Senior Design Engineer of Philips that I do. But basically the motor is running flat out, and what we do is to basically reduce the torque and smooth out the whole system. No good for scratching, but great for Hi Fi.