Hi Everyone , I had a question

I have an stereo amplifier , with 2 channels for Play , 2 channels for Phono1 and Phono2 , one channel for Tuner and one channel for AUX .

my two play channels are failed and i'm currently use the tuner channel for my cd player and everything is fine . I want to know that What's the difference between these channels (phono 1 , phono2 , tuner , aux ) and what is the usage of AUX channel ?

thanks so much