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I'm transmitting analog audio signal from BM20 bluetooth module (it has single ended audio out L + R), to amplifier TPA3118D2.

I wish to add two TRS 1/4 balanced audio output jacks (separate for L and R channels).

I'm controlling AMP mute/unmute via my MCU and also wish to have plug/unplug signal from each audio jacks to handle amp muting.

I'm not good into analog audio, thus I don't know what consequence will below setup have? Will it work properly? I thought about using shield switch but I don't know if it is safe to connect jack shield to system ground. TRS balanced audio output switch earth

I could have use jack switches to just control audio path (to amp or to jack), but that will mean that both jack plugs have to be inserted to completly mute TPA3118D2 amplifier.

Mateusz Kusmierz
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  • Note there are TRS jacks available that have internal switches which aren't electrically part of the T, R or S. – Kyle B Nov 14 '22 at 21:24
  • Also note, when you insert or remove a TRS, the contacts will usually briefly short circuit together. Make sure your circuit is tolerant of that. – Kyle B Nov 14 '22 at 21:27

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I would use the sleeve switch (pin 7) as the plug insertion indicator. The sleeve (which connects to the cable shield) should normally be connected to system ground.

I would not use the tip and ring switch contacts.

Peter Bennett
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  • Is it safe to connect sleeve to system ground? Pass it directly or through some sort of ferrite bead, capacitor or resistor? What will happen if sleeve will have live/high voltage (in case of long audio cable being broken, or bad audio equipment)? – Mateusz Kusmierz Nov 14 '22 at 19:55
  • It's not only safe but proper to connect the sleeve to ground. If you've got high voltage on your cable grounds you've got a serious safety issue you need to fix. Don't use the tip or ring shunt because then you'll have to worry about the audio signal harming (exceeding max/min voltage) of MCU pin when no cable is inserted. – td127 Nov 14 '22 at 23:52