i don't know what a phono preamplifier is. could you please explain what does that mean?

otherwise i have two turntables that are plugged into the mixer, and the mixer is connected to a stereo receiver which then sends the signal to the speakers.

the mixer that i use, is JBsystems Beat 4. i don't know if it has a phono preamp. how do you mean that maybe one works and the others might not (if that were the case)?

it's strange because one turntable works on all the channels and the other two (mine and the borrowed one) don't work anywhere.

i tried another mixwer also, it's a cheap one basically, but it did the same thing. so the problem should be in the turntables? but the problem is, that when i take my nonworking turntable to a friend, it works there normally.