Mic Preamp Mult Outs for Simultaneous Live Monitoring and Direct Recording

[MountCyanide]

Greetings all. As my workflow isn’t completely constrained to the computer, I monitor my synths and drum machines through my mixer as I compose. Pro Tools playback goes through the mixer to so I hear everything already recorded. I’m about to make a move to the other coast and as I will be downsized for the time being I’ll be without my trusty PM-2000 console. Instead of the mixer I’ll be running all of these instruments into the mic preamps in my 500 rack. I’m devising a circuit that’ll take dsubs in from the mic preamp outputs. Those will be routed directly to a dsub output and into my converter for recording. But in between that I’ll be pulling a tap from each channel to a summing mixer.
From that tap here is the signal flow I have in mind:

1. Buffers (?)
2. Line Receiver (Differential In - Single Ended Out)
3. Fader
4. Post fade amplifier
5. Pan pot
6. Summing
7. a) Monitor Out
    b) 2-Track Out

The question I have here is do I need to buffer these differential signals before entering the line receiver so as to not muck up the direct signals going to the recorder? I would probably use a dual IC, one amp for each + and - in unity gain mode then out to the line receiver. I’d be stoked if I could get away with not needing to buffer but I’d love to hear some thoughts.

 

[john12ax7]

I do something similar now.  My 500 series rack has both dsub and XLR,  one out goes to the computer, the other to an inexpensive line mixer.

I don't think a buffer is necessary if both computer and mixer are typical modern high impedance inputs.  You will have some extra cable capacitance and loading from the 2nd line, but in practice I haven't noticed any issues. Keep cable lengths reasonable and it should be fine. If you are designing the mixer you could  choose to make the inputs higher than normal, but it's debatable if that's even necessary,  a typical 10k input shouldn't be an issue.

 

[MountCyanide]

Excellent, thanks  John.
Which rack are you using that has both of those connections?

 

[pucho812]

as long as you are dealing with modern inputs and the runs are short, just mult the channels so that the output goes to two spots.  It should sound fine with minimal, if any difference, usually not enough to notice.

 

[MountCyanide]

That's awesome.  Thanks pucho. I'll make the input impedance high like John said and utilize 20k resistors all around the opamp giving me an input impedance of 40k at the differential receivers.

 

[john12ax7]

Excellent, thanks  John.
Which rack are you using that has both of those connections?

It's the newer API 6 space lunchbox,  with rack ears attachment.

I think the RND Neve ones also have dual i/o, probably some others as well.

Redco has db25 mult boxes and various different enclosures if you need to build something.

 

[MountCyanide]

Ooh those Dsub boxes look handy and save some labor for pretty cheap. I’m actually moving to 15 min away from Redco.