What would be the best way to connect a turntable to mixer? Do I need an external phono preamp? Or can I use the preamps of the mixer?
You’re going to need a proper phono preamp if it’s to sound any good. Some more modern turntables appear to have these built in now.
Yeh-- you need a a phono stage – the signals from a cartridge are very low and need special RIAA equalisation. In fact ideally you need to match them to the type of cartridge you are using (moving magnet or coil). You can buy phono stages separately or, as Mark says, they do come built in to some turntables. Most higher end older pre-amps would have a phono stage.
You can buy a turntable with USB output. I have one for ripping LP’s directly into my computer.
I’ve got one too, and while the A/D may be good enough, the mechanical parts are shockingly bad.
Previous entries have answered your question. One key thing to know is that RIAA equalization is required for a phono cartridge.
I’m not sure what you are planning to do, but perhaps just DJ work. However, if you want to get rid of some of the noise - click, pops, some hiss - usually heard on LPs, for archive purposes, you may want to use a computer with software that has noise reduction capability. There are several programs just for this sort of thing.