XLR mic summer

[alexanderbrevig]

Hi

Short background/context: I run my own side business as an audio engineer. The most frequent clients are choirs.

What I want:
I want to sum the choir microphones on stage into their respective voice type/group. Instead of 40+ lines from stage to console I could run four, and use four pre amps on my mixing console.

I do not require more control than level of each mic, and I've guessed that I need to buffer/drive the outputs before getting to console pre amp. Maybe completely passive would suffice?

I'm going to do prototypes, but wanted to check before I do so I don't mess with the rather expensive equipment.


I'm still very much in the process of learning, and I've made a schematic of what my current ideas and understandings are (attached as altium exported pdf).

Any and all input are much welcome! The current design is a mashup of what I've read and seen online so far, and most values are guesstimates...

MORE INFO:
I own the mics myself (AKG D5) so I have relatively good control on the type of devices that plug in. But I have a question: Would Phantom Power (45 volt feeded from desk to mic) be affected too much by the current design?

PS: after the schematic is working I will also add digital circuitry to control the 'levels', so total lines from front of house to stage is 2 per summing box (xlr sum + xlr serial TX)
PS2: and of course, I will open source everything

[alexanderbrevig]

RE: Use Caps; I'm not sure I understand how this would be wired up unfortunately.
I see two scenarios:
1) Given that I must supply phantom to each mic, I will place phantom power (PP) circuit between DS1882 and XLR connector. Then, we can use caps between PP and DS1882 to block dc, correct? (how would I go about finding good farad values?)
2) Given that mixer can enable PP, do we need to protect on the side of output xlr too (#XLR2)?

RE: OpAmp; Just read the datasheet and saw the opamp application note. Thanks for pointing it out.

RE: Full differential; I will look into that, what is the current configuration called? As I said, I'm new to electronics, and passives in particular (worked a bit with digital µCU stuff) - so I'm trying to learn and gain knowledge and intuition on these things.

Thank you so much for your answer @blueskull!


Do you think I need the opamp driver?

Do I need to shunt the Tip and Ring on the output side? I think the preamp typically expects ~150ohms but the mics will be the load/impedence right?

[alexanderbrevig]

I'll do some more research, update the schematic and post here in a few days. Thank you again for excellent input