Amp Harmon

How to ground a turntable to a surround sound amplifier?

I have a Harmon Kardon amp and have recently hooked up a turntable to the Cd input.I had to use a small Radio Shack preamp inline to boost the signal.The preamp has a ground which I attached to the amp ground screw.The turntable,however is a turntable used to convert albums to wav or mp3.It has no ground but has a usb port and a gain knob,as well as a switch indicating “RCA phono line” and “RCA line” .At a high volume there is a distinctive buzz .When I put the preamp in a slightly different position or touch my finger to the RCA jacks the buzz gets better but never goes away.Any ideas?Peter

You have to connect red & white cables from turnable to phono input, not to any inputs on receiver.

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