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Is it possible to add PTT/Mute to a 3-pin standard terminating XLR cable (with +48V phantom power)?

In my case, I have found myself with a Astatic 40-119 microphone base with a PTT switch that "only" provides dry contact between the 4 & 5 pin of the 5-pin XLR cable. Can I use this fact to cut the power to the condenser mic, or is there some better circuity to accomplish the mute? The base works great otherwise. (There is a competing model that mutes the microphone on a standard 3-pin XLR cable that I've included the spec sheet for completeness.)

  • 40-119 MIC BASE Spec Sheet

    This unit features a dependable momentary push switch that provides a dry contact between pins 4 and 5 of the cable terminating XLR connector. The switch can be configured for either "push-to-open" or "push-to-close" using the slide switch located on the underside of the base. The 40-119 base is used to control an independent device while audio signal from the mic is always on.

    Just to note: the mic does work as described. Maybe the mentioned "independent device" can mute the mic :)

  • 40-116 MIC BASE Spec Sheet (don't have this, for comparison)

    The circuit contains a highly reliable switch to operate a 55dB mute which will effectively kill audio output without causing a potentially damaging phantom power "thump" when used with electret type microphones.

These questions were helpful to me but the first two are microcontroller focused. The latter 3.5mm also has a power component, I'm researching into it more.

  1. Microphone mute anti-pop circuit works but still picks up a little audio
  2. 5v Electret microphone to PC mute switch pop help
  3. 3.5mm Push to Talk Switch

Any help would be appreciated.

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    \$\begingroup\$ I have read the 40-119 "datasheet" and didn't find it terribly useful. It might be that pins 1,2 and 3 of the 3-pin XLR go straight through to the 5-pin XLR and pins 4 and 5 of the XLR are attached to the switch. I'm not positive about this. If it is, then yes, a simple circuit with at most 1 capacitor and 1 or two resistors should be possible for push-to-talk. Hardware required is one 5-pin XLR connector to plug into the base, and one 3-pin XLR connector to connect to the cable taking the signal from that circuit to some external device/amplifier. \$\endgroup\$ May 6, 2021 at 19:06
  • \$\begingroup\$ pin 1 carries the phantom power, pins 2 and 3 are the differential audio signal , grounding one of them will make a loud pop. \$\endgroup\$
    – Jasen
    May 7, 2021 at 2:18
  • \$\begingroup\$ @Jasen, per wikipedia, a three pin XLR has pin 1 is ground, pin 2 is hot, and pin 3 is cold. My understanding is phantom power is connected to the hot pin (and the ground). \$\endgroup\$ May 7, 2021 at 2:45
  • \$\begingroup\$ That's not how phantom power works on balanced microphones. everything you've learned about phone jack micorphones is inapplicable. \$\endgroup\$
    – Jasen
    May 7, 2021 at 2:52
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    \$\begingroup\$ It's ground, but it's only used to complete the phantom power circuit the audio is on pins 2 and 3 and it not ground referenced. \$\endgroup\$
    – Jasen
    May 7, 2021 at 2:54

1 Answer 1

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Set the switch mode to push to open and connect it across the signal lines. (pins 2 and 3)

releasing the PTT will mute the microphone signal by shunting it.

So, connect pin 4 to pin 2 and pin 5 to pin 3

With a 20 foot cable this may not work very well. if you are allowed to modify the base make the same connection internally instead.

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    \$\begingroup\$ Is shunting the microphone signal a good idea with phantom power applied? \$\endgroup\$ May 7, 2021 at 5:53
  • \$\begingroup\$ It's common practice, microphones have high impedance so there no change of damage. \$\endgroup\$
    – Jasen
    May 9, 2021 at 1:48
  • \$\begingroup\$ wouldn't that short out the phantom power? \$\endgroup\$ May 9, 2021 at 10:25
  • \$\begingroup\$ no because ground is the return for the pohantom power and it does not connect to ground. \$\endgroup\$
    – Jasen
    May 9, 2021 at 11:00

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