I tried running my computer audio output and my tape player through the preamp, and it worked well. (They do not need that, but I did it for the sake of testing).

Just a few minutes ago I thought about connecting the grounding wire to a power outlet's grounding post, but for that I need to modify the power and the grounding wires of my turntable. I can cut off the original plug, buy a 3-pin plug and safely connect the power wires and the grounding wire to it, after which it will be easy to use. Do you think it will work?

Thanks.