the K8004 is a good kit if you want to begin to understand the basics of PWM control -- you can also use PWM for myriad applications BUT...
if you are driving a turntable platter PWM is probably NOT the way to go -- while you can tightly control the pulse width through the error amplifier, you are still pulsing the motor so the speed is always accelerating and decelerating a bit -- the integration is provided by mass and velocity of the turntable platter !
the SG3524 or SG3524, coupled with an H-Bridge chip like the LMD18200 or LMD18201 (or equivalent chips from TI and others) are great devices for robotics.
http://www.tech-diy.com/jobo.htm