Have a turntable with no pre amp. Purchased one and used a converter cable RG to HDMI to sound bar but no sound.
Then tried to TV Samsung TV direct no luck.
The pre amp was a cheap Selby brand.
What exact turntable, what exact preamp model, what exact sound bar and what exact cable? Not sure what "RG" is here. Most likely issue is the soundbar is not getting the signal it needs to work through HDMI, it may need a video not just an HDMI audio signal to work. It may also be whatever cable you got does not work.
What exact cable? RCA to HDMI would need some sort of an active electronic converter. If you don't want to mess with adapters, converters, etc... read the last paragraph.
That preamp is also run on battery only it seems, did you check the battery to make sure it's OK? Would be a good idea to test the setup through the pre-amp to some normal speakers/receiver to make sure that side is all working before trouble-shooting past that link.