XLR with/without phantom power capacitor question

[todd.dukes]

I have the following circuit for a 2 channel mixer with XLR out and a headphone amplifier with a local solo feature.

I want this to tolerate someone accidentally turning on phantom power. The way it is drawn C2 and C3 are oriented for phantom power to be off. If phantom power is applied, C2 and C3 are reverse biased by up to 48V. If I swap C2 and C3 around and phantom power is not applied, then they may be reversed biased by 4.5 volt.

I could replace the 220uF with a large MLCC cap. (The biggest I have is 1uF) But I would lose low end (cuttoff would move to 160Hz) and I have heard bad things about MLCC with high DC bias voltages.

How is this normally handled?

[todd.dukes]

I changed to B/W color scheme for the schematic. How do I delete the other image?

update: I figured it out.

[merlinb]

How is this normally handled?

Make your own non-polarised caps by putting two 50V caps in series with opposing polarity.

You also need diodes from the output of each opamp to the rails, to protect them from the energy that will be dumped into the output when phantom is turned on. Ala: http://rc700.dk/peter/diverse/output-protection.png
You should really have pull-down resistors right at the output too, to allow the caps to charge at switch on and prevent a pop when the cable is plugged in.

You also need DC blocking caps before R11 and R12 (I suggest simply moving C5 and C6), possibly also a blocking cap after U1, but I'm not sure what it's driving?

I don't know what headphone driver that is, but are you sure it doesn't need blocking caps before R14 and R16 (move C11 and C12?), and also at both outputs?

[merlinb]

Also, bottom U1 and top U2's inputs are back to front (+ and - need to swap).

[todd.dukes]

possibly also a blocking cap after U1, but I'm not sure what it's driving?

I don't know what headphone driver that is, but are you sure it doesn't need blocking caps before R14 and R16 (move C11 and C12?), and also at both outputs?

Normally U1.1 is driving FS1 which goes to U2.2
In local-solo mode U1.1  is driving FS2 and FS3 which go through the pot and feed the headphone amp. The idea is that I can either get headphone-out from the headphone-in and drive the house (normal-mode) or I tie the house to ground and drive the headphones with my signal (local-solo-mode). The two inputs G1 and G2 are for my magnetic pickups and piezo pickups. I have a switch on my guitar to select between them.

The headphone amp is the MAX9722 so the output caps aren't needed. I do need to reconsider the blocking caps between the stages for both modes of operation.