Earth hum from pre-amp

[Jula]

Hi All
First post.
I have a Denon tuner/amp/CD system and I'm using a legacy turntable (a JVC in fact) from a previous old combo system. After buying my Denon and discovering that I needed a pre-amp I bought a very cheap one from Richer Sounds.
Trouble is I have a really bad earth hum whenever I play vinyl.
Admittedly I have loads of stuff using the same 13 amp socket DVD player, TV, Freeview box etc, most of which don't have an earth cable and when I unplug them it improves radically, but I noticed that my cheap pre-amp also doesn't have an earth cable (just one of those plastic blank pins on the plug).
The turntable itself is also without earth.
Any suggestions gratefully received.
Thanks