Yes, the TAPE IN jacks are intended as the returns from your multitrack tape machine; should be connected to the tape machine outputs. You don't need any kind of summing mixer onboard the tape machine or in between the tape machine and the console (so no need for "just a stereo out" from the tape machine). What I was saying wasn't meant to indicate you don't use the TAPE IN jacks.
Come...take a walk with me...look at the jack panels for each input channel. How many inputs do you see? Not counting the RCV jack you see three for each input channel, right?
Channel 1: MIC, TAPE and INSTRUMENT inputs
Channel 2: MIC, TAPE and INSTRUMENT inputs
Channel 3: MIC, TAPE and PHONO inputs
Channel 4: MIC, TAPE and PHONO inputs
Channel 5: MIC, TAPE and LINE inputs
Channel 6: MIC, TAPE and LINE inputs
Channel 7: MIC, TAPE and LINE inputs
Channel 8: MIC, TAPE and LINE inputs
Channel 9: MIC, TAPE and LINE inputs
Channel 10: MIC, TAPE and LINE inputs
Channel 11: MIC, TAPE and LINE inputs
Channel 12: MIC, TAPE and LINE inputs
Channel 13: MIC, TAPE and LINE inputs
Channel 14: MIC, TAPE and LINE inputs
Channel 15: MIC, TAPE and LINE inputs
Channel 16: MIC, TAPE and LINE inputs
Channel 17: MIC, LINE and 2TR A inputs
Channel 18: MIC, LINE and 2TR A inputs
Channel 19: MIC, LINE and 2TR B inputs
Channel 20: MIC, LINE and 2TR B inputs
"My goodness" you say..."That's 60 inputs! But I only have 20 channel strips, so its really just like 20 inputs, right?"
Nnnnnnnnope.
You can actually monitor two of the three inputs simultaneously on each channel strip, and in multiple ways.
So you're going to connect the outputs of the MS16 to TAPIN IN jacks 1-16 on the M-520. You know you use the INPUT source select toggle switch at the top of the channel strip to select the source of the channel strip, right? You typically have those set to MIC or any of the secondary input sources during tracking (the INSTRUMENT, PHONO or LINE inputs for sources of those types, if applicable). You flip them all the way to the right to TAPE (on channels 1-16) during mixdown. So during tracking you have simultaneous access to any combination of 20 MIC, INSTRUMENT, PHONO or LINE inputs sources.
So now you're still going "Right, sweetbeats, I get it already, but how am I supposed to monitor playback of my tape tracks as I fill tracks during overdubs? HOW?!?"
Each input channel has three possible sources, and as noted above you can select one at a time as the main input for each channel strip, but look at the AUX 1/2 and AUX 3/4 source select toggle switches on input channels 1-16. What do you see? They look like this, right?
PRE POST TAPE
Tape? Yes. Tape. You can set the source of the AUX busses on channels 1-16 to the TAPE IN jacks independent of the input source setting of the channel strip. This is called inline monitoring, where a channel strip can discretely monitor two or more separate inputs at once. You could have channel 1 listening to the MIC input (channel INPUT source select toggle switch set to MIC), but AUX 1/2 (for instance) listening to the TAPE IN 1 jack (AUX 1/2 source select toggle set to TAPE). So then during tracking and overdubbing, if you used (for instance) the AUX 1 or AUX 2 buss (or *both* to create a stereo mix...ask me if you don't understand what I mean there), any AUX 1/2 source select switch set to TAPE will be listening to that channel's corresponding TAPE IN jack, which corresponds numerically to the same numbered tape track, you turn up the AUX buss level knob, then raise that AUX buss' master fader, depress that AUX buss' button in the MONITOR SELECT switchrack in the master section, and then in the headphones and at the STEREO A and B out jacks will be your submix of the tape tracks you are monitoring via the AUX buss knobs on your input channels. Its a mix within the mix. And you have options. Let's say you're like "But sweetbeats I need all my AUX busses for cue feeds of input sources for the talent during tracking as well as for effects sends for wet cue feeds and some wet printing to tape." Look at the 16 channel monitor mixer you have there above the PGM group faders. Each of those 16 channels also has a source select toggle switch...yes? Looks something like this?
BUSS | TAPE
When set to "BUSS" that monitor mixer channel is listening to the post fader signal of the PGM group fader directly underneath it. When set to "|" that monitor mixer channel is off. When set to "TAPE" that monitor mixer channel is listening to...guess what? The numerically corresponding TAPE IN jack. You can monitor all 16 tape tracks at any time via the monitor mixer. It is another 16 x 2 mixer within the mixer. Set your source select toggle switches to TAPE, set the LEVEL and PAN knobs to taste and you have a completely independent monitor mix of all 16 tape tracks. This is actually what the monitor mixer was intended to do when interfacing a 16-track tape machine with the M-520. Then you depress the MON switch in the MONITOR SELECT switchrack in the master section, and in the headphones and at the STEREO A dn B out jacks is the stereo sum output of your monitor mixer.
So that's how its supposed to work. During tracking and overdubs you are using the primary and secondary inputs to the channels for your sources you are tracking, your tertiary inputs (the TAPE IN jacks) are monitored via an AUX buss (or two if you need a stereo cue mix of your tape tracks) for the talent or you as the engineer, you have additional AUX busses for send effects if the talent needs that reverb in their headphone mix OR if you are printing any tracks to tape wet, and the monitor mixer is for you as the engineer to monitor a stereo mix of up to all 16 tape tracks. If you are using program groups for a stereo submix of your input channels or as additional sends or submixes to tape, you can monitor those PGM groups via the monitor mixer by setting monitor mixer channels to "BUSS", but if you are using all monitor mixer channels to monitor the 16 tape tracks, then just take the relevant PGM OUT jacks and patch them to the SPARE input jacks, or if you aren't using either or both of your sets of 2TR A or 2TR B inputs you can patch to there as well, and then depress the corresponding switch in the MONITOR SELECT switchrack. Now your PGM group stereo mixes or individual PGM groups can be heard in the headphones or at the STEREO A and B out jacks. You can also use the MON SUB IN jacks this way, and have any two channels' outputs riding along with the output of the monitor mixer, and monitored via the MON switch in the MONITOR SELECT switchrack. Typically you aren't needing to monitor all 16 tape tracks during tracking and overdubbing, because if all 16 tape tracks are full, its time for mixdown. And furthermore I'm usually not needing to listen to all tape tracks that I have recorded at any given point while tracking and overdubbing anyway...I'm monitoring inputs, and key tape tracks. So that often leaves multiple monitor mixer channels idle, and those can conveniently be set to "BUSS" to monitor PGM groups. But the monitor mixer CAN monitor and mix all 16 tape tracks simultaneous, and in that case you have those options suggested above for monitoring PGM groups you are using.
Does this make sense? The M-500 series consoles aren't like conventional basic mixers...Your M-520 isn't just a 20 x 8 console...it is a 20 x 8 console with a semi-configurable 16 x 2 nested within, and each of the 20 input channels can monitor, if needed, two inputs at once.
