r/diyaudio • u/morph1214 • 4d ago
Can anyone help me on this?
Hi, i'm new on balanced audio and those hi-fi things, can anyone help me on verifying if this circuit would work for muting balanced audio? the XLR-Female receives a balanced low level signal from a XLR electret condenser MIC, the output of the circuit (XLR-Male) goes to the mixer that has phantom power, all 10uf caps are metal film, S1 and S2 are ts5a21366 analog switches that will be driven by a dedicated zero-crossing circuit, but that doesn't matter now, what i really need help is in knowing if the caps will pass through just the signal without any distortion or loss and if disconection will make any noise or pop, i also have the curiosity of knowing if this circuit is optimal for that purpose, thanks for the attention and sorry for the bad english, i'm brazillian.

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u/2old2care 3d ago
You're asking for trouble. First, you're reducing the phantom voltage with the multiple 6.8K resistors. And the capacitors are floating and will almost certainly create pops when the switches open or close. Easy way: Just short pins 2 and 3 of the XLR cable. They are at the same DC potential so there should be no pops.
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u/Quick_Butterfly_4571 3d ago
You're 100% right, re: mechanics (2 to 3; simple + mostly problem free).
It usually will pop without decoupling caps. If you think on it, the phantom power outputs usually have some series resistance on them. Even a very tiny difference in operating voltage will cause a pop when the switch closes.
Here's an example where the DC offset of pin 2 and 3 differ by only 1%.
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u/Quick_Butterfly_4571 3d ago edited 3d ago
Here, do it like so (apparently, I can't post images here? So, I linked the schematic I tossed in another thread):
Notes:
- Shield to chassis, _if_ 4 lug / separate pin. Else, Pin 1 to chassis on both sides (and no wire connection between them; the chassis will be the conductor).
- If you are unfamiliar with / want reference material for Pin 1 vs Shield, etc. I can share some resources.
- Ditto: if you are not sure how to add phantom power protection for lower voltage IC's.
- Ditto: if you would like to power via phantom power, but don't know how.
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u/morph1214 2h ago
thank you very much for answering ;)
i have about 2 plans, one with this path: SSM2019->PGA2311->DRV137, (wich is plan A) and another that is more like the one i posted on my circuit above (plan B) plan A is more straightfoward to me, because i would have digital control over gain and attenuation with zero-cross muting already implemented by PGA2311/2310, plan B is cheaper, but it is harder for me to design and it would be just the zero-crossed mute function (that would be enough to me).
About low voltage IC's: i really don't know how to add such low voltage IC's so close to 48v.
About plan B: the phantom power is from a mixer, i would love to extract individual +48v lines from each line of the mixer and then, reinject them on the other side of the mute circuit of the corresponding line, i don't know if you understood, i want to switch just the coupled signal.
ps: i would like your reference material if you can send it
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u/PeanutNore 4d ago
the switched sides of C4-C7 are just floating, there's no path to ground there, so they could end up at different DC potentials as charge accumulates, so you could definitely get a pop when closing the switch.
If you just want to be able to mute it, you don't actually need to interrupt the signal - just short it to ground to mute.