Question about Lenco L-3808

It always depends on the tuner system. Whether it has its own earthing or not.
If not, I recommend a preamplifier. There are expensive ones, but also very cheap ones. I bought one from Hama and haven't had a single problem in two years.

Hama PA 506 (MM, Entry)

Your record player already has an integrated stereo preamplifier. So you should be able to play the audio signal over your stereo system via an AUX input (cinch) without any problems.
And record your tracks via USB on your computer. :-)

And the manual says the following under point 22:
22.
RCA OUTPUTS
The output is a switchable PHONO/LINE output. For example: These output jacks send a low voltage "phono" output signal to the "phono" inputs of a mixer. Record players must be connected to the "phono" inputs of a mixing console. The red RCA jack points to the right input channel
input channel and the white socket indicates the left input channel.

So have fun with it. :-)