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I want to make a phantom power (PP) mic mute switch with an indicator led powered by PP. I already did it based on the following circuit. It works but, with the led included in the circuit, I get a pop when turn On-Off the switch. Without the led it work fine and silent.

schematic

simulate this circuit – Schematic created using CircuitLab

Is it possible to prevent this pop keeping the led being powered by the PP? Or there any contraindications of powering the led with PP?

Please, help me. I'm not electronic engineer.

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2 Answers 2

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I'm assuming balanced lines with 48V phantom power like is used with Cannon XLR connectors

you need to ensure that the draw for the LED is balanced across the signal lines, you can either do this with a transformer with a centre tap.

schematic

Or by making the circuit symmetrical.

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  • \$\begingroup\$ FWIW, I built a separate symmetrical circuit (it uses two 3.3 kOhm resistors) but it still pops a fair amount. Part of that, I'm sure, could be that the switch isn't ideal; it's break-before-make. (And even make-before-break would have this problem.) I think you'll need some active logic for this to work. \$\endgroup\$
    – Jon Watte
    Apr 20, 2021 at 20:38
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I know it is an old thread, but here goes. Have you been able to fix this?

I wonder if the pop is due to differences in the resistor values within their tolerance bands. That throws the required symmetry off. The 6.8K resistors used on pins 2 and 3 in the phantom power circuits I have looked at have a tolerance of 1%. I would therefore think that the best you can do with a simple circuit is use 1% or better. You could also try matching the resistance values as well.

NB: Also thinking that you could still get a slight spike (a pip rather than a pop?) as the audio from the mic would unlikely be dead 0 when the mute is activated.

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