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). Typical application from the manual

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


2 Answers 2


2T is two track - ie a stereo recorder.
Send/output to the recorder is 'REC'
Return/playback from it is 'RTN'.

Presumably designed for consumer audio [cassette deck etc as in the picture] as it's on RCA & not any 'pro' format.
I'd guess it's for consumer line level not headphone level. As to whether you can 'safely' use it - that kind of mixer is likely to be 'OK' at many impedances/output voltages but, short of a full spec manual*, the only real way to find out is to try it & see.
Start with your device outputs set at minimum & see how far you can turn it up before you can hear distortion, then back it off a bit.

*I found one here if you want to go through the spec - https://www.manualslib.com/manual/1200265/Phonic-Mm1705.html#manual

  • 1
    To OP : notice that the 2T RTN is (probably) not another channel input, you can not mix it with other channels, I suppose there's a RTN selector somewhere near the monitoring section of the mixer.
    – audionuma
    Commented Jan 7, 2023 at 18:39
  • @audionuma - tbh, I didn't look at the manual myself to check any of this. Now I do… I realise it's in Japanese ;))
    – Tetsujin
    Commented Jan 7, 2023 at 18:47
  • @Tetsujin i can share the manual mega.nz/file/…
    – Enrico R.
    Commented Jan 7, 2023 at 22:45
  • 1
    @audionuma there is a knob that controls the level sent to master LR
    – Enrico R.
    Commented Jan 7, 2023 at 22:49
  • My wrong. As @EnricoR.mentions, you can actually route the 2T RTN to the master LR. Forget my comment.
    – audionuma
    Commented Jan 8, 2023 at 8:28

Some high end tape recorders allow you to actually listen to the recorded matter while recording it. There will be a delay and the quality is generally not as high as the regular full size "playback" head.

On my Pioneer amp, when I hit Tape Monitor is like switching to the tape channel, press again to return to previous channel. It does that so I can hear the recorded tape. If I had switched my amp to listen.... well there would be a big feedback because I have my amp "tape out" going to the recorder, it would start to record itself. Using Tape Monitoring with selector set to CD or the source continues to send the CD sound to the tape, but the speakers begin to play the currently recording tape. Nifty.

Therefore your desk should send the master channel to tape send just ahead of where it blends the monitor into master for your speakers, otherwise massive squeels of feedback should occur.

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