My mic "Panic" switch

I want to rig up a panic switch for use on stage so the singer can mute the FOG and still talk to the in ear monitors the band wears. I drew this up inspired by RG's article on geofex and thought I would post here for comments/suggestions. I've learned a lot from reading this board and hope this is helpful to someone.

Essentially uses optocouplers to isolate/mute the PA input from the mic source which is hardwired to the monitor input. Actually the way I'll use it is two separate channels on the same board, with one muted in the house. I gather that the limit suggested for passive splitting without a transformer is 3x so two outputs should be fine.

It may turn out that I want to boost the singer volume in the monitor when muted in the house so I may insert a second set of switches for the monitor out that operate inversely to the switches for the front of house, so that I have a real A/B instead of A + B. This way I can set the level of the singer from output A in the monitor mix, and mix in more of B so that when the panic is hit the singer will be clearly heard over the rest of the mix.

Any problems I'm not seeing? I think this should be click free but any extra insurances?

AKA "coff" switch, except it does not cut the foldback.

Resistor values not shown; but IIRC that opto likes 10mA-16mA. Since the two main LEDs are driven parallel that sucks 20mA-32mA for most of the performance. (If fed series only 10mA-16mA.) If 9V battery, you'll need a new battery every night.

In much live performance work a DPDT mechancial switch might do the job power-free, and without the added impedance (hiss) to the mike preamp.

Hiss is due to resistance. Mike may be 100 to 300 ohms. H11F1 adds 200 ohms per leg, 400 ohms of dead resistance. The hiss in mike is kinda inevitable to capture signal. H11F1 does not add signal only hiss. Yes, I've seen much higher dead-resistance tolerated in stage work.

But WTF. It's like five-bucks of chips, and WOULD work well in guitar-cord switching. So try it in the mike.

If you need Phantom and it comes from FOH, you go dead when you break the FOH line.

In such a case with the series resistance, perhaps using solid state relays would be a better option. Some have on-resistance below 40 ohms. I think I have one or two around so that i might try first.

I haven't seen a schem of the proco box or any other coff/panic switch but I assume every unit would have some degradation or noise. If I used an isolation mic with a relay shunting the two signal wires I suppose that would have the least noise. No series resistance with a good quality transformer? Is there a better theoretical way to do this?

Wouldn't some adequately biased j111's and some logic do the trick?
Maybe a T-Switch?

great notes in douglas Self's latest small signal book on switching audio.

/R