Audio PA 1 mic for 2 devices?

By bus_man ·
I'm trying to use one microphone to work with 2 separate devices (a PA and a 2-way radio). It would have two independent Push-to-Talk (PTT) switches to activate each device, so essentially, when you push one PTT you activate the mic with the PA and not the 2-way radio, if you push the other PTT, you would use the same mic with the 2-way radio and not the PA.

I designed a harness that feeds the audio MIC+/- from the microphone to both inputs of the devices, and 2 switches on different PTT circuits to each device. However, I'm concerned about noise because the MIC +/- from both devices are tied together. Is this a legitimate concern? Is there something out in the audio world that already does this?

Hope you can help!


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Cross Feeding Power

by TheChas In reply to Audio PA 1 mic for 2 devi ...

Thinking about this, my primary concern would not be noise but the fact that if you tie the 2 microphone inputs together you can end up cross feeding DC power between the 2 systems.

I don't know PA systems in depth.

I do know that most 2 way radios use powered microphones. There should be a measurable DC voltage between the microphone + and - leads. If so, unless both preamps use the same voltage level and share a common ground, you risk damaging 1 or both microphone inputs.

The best way to share a microphone and isolate the 2 devices would be to use a 4 pole double throw switch. Wire the microphone to the center or common contact. Wire 1 device to the N/C contacts, the other to the N/O contacts.

You could also do this with a pair of 4 pole momentary switches and use them as the PTT switch for each function.

The local amateur radio club should be able to point you to sources for parts or even a ready made box.


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by bus_man In reply to Cross Feeding Power

hey Chas,

Thanks for the input, and good advice!
yeah, my other design was to use relays in a similar fashion as you described. But, I was hoping to avoid that or see if there was already a product out there that could do this.

Relays it is. =)

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As for existing products

by OH Smeg Moderator In reply to Thanks...

Any Mic Switch should do this.

The only reservation I would have between a PA and Two Way is that they may require a different type of Mic. Most PA Systems don't use the cheaper Mic's that the 2 Way's do. Also most PA's do not have Noise Canceling Circuity which most 2 Ways do.


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