I am studying the manual of an old Phonic MM1705 mixer.
Then I see 4 RCA connectors: 2 for 2T RTN and 2 for 2T REC. From the manual, they are used together for recording to audio cassette (see below).
Thus, 2T RTN line seems a sort of feedback line from the recorder (may be to wipe noise?). But I cannot find any info (neither on the internet) about what 2T means. Do I need to use always both lines? Can I safely use the first for PC/smartphone connections?
Note that, for "CD input" the manual suggests one of the stereo channels 6/7, 8/9 and 10/11