I would say you need at least 60db. 66db would be better. It really depends on how quiet the phono stage is. If it claims to have 70db gain but has a high noise floor then you can't really use that 70db. It is very difficult to get high gain and low noise at the same time. It's even more difficult to have both and good sound as well.
Phono Preamp Gain Question
I am looking to upgrade my phono preamp as I have just acquired a much better cartridge. The cartridge has an output of .28mv; my tube preamp has gain of 12db. What is the lowest gain that a moving coil stage of a phono preamp should have for me to listen without excessive noise? I listen at realistic levels--medium to loud. I have read that some of the newer phono preamps without transformers--ARC PH6 or CJ TEA2se to name two, will not have enough gain for my application. Thanks in advance for your help.