PLX 500 crackle hum when connecting to vintage NIKKO solid state amp....help

I'm really struggling to connect my record player to my vintage Nikko amp. The amp does have left and right phono connection so plugging directly in from the 500 with no need for grounding wire as deck is apparently grounded and no need for pre-amp as 500 plx apparently has a built in pre-amp but there is an unbearable loud crackle sound as soonas you connect, when you turn knobs, in background when playing and when nothing is playing. I tried switching to line and using a different connection but the sound is still there. I've used the amp with a different turntable and it works but that turn table has a grounding wire. I just can't work out why the distortion ...do i need a pre-amp, perhaps it does need a ground wire or I have to ground the amp but to what and how ? or something else I've missed. I really like the sound of the Nikko Amp and unpowered speakers so really want to get this set up working any ideas???