Is it OK to put turntable on top of amplifier?

Most stereo receivers have the transformer on the left side, so putting the turntable on the right side of the receiver is recommended. We strongly recommend not placing your turntable on top of your receiver - this can cause buzz issues and may also prevent your receiver from getting proper air flow.

Do I need a preamp if I have an amplifier?

No, a preamp cant be used as an amp because they do different jobs. A preamp boosts weak signals to line level, whereas an amp boosts the line level so it can be heard through speakers. Although their jobs are similar, you couldnt replace an amp with a preamp, or vice versa.