If I can get a relay that would work at such low currents/voltages

[viviantern]

Its that time of year when I revisit one of my old projects and try to improve it. Currently I have a small 12v PA system that has a microphone and I've added an 3.5mm auxiliary input to play music over it. Right now I'm using a 3 point switch to toggle between the two.

This is kind of annoying because I have to switch between the two manually. I'd like to change it so that when the microphone is in use, it automatically switches from the aux input. The microphone attached to the PA system has a toggle switch so I'd like to detect when its pressed and switch it over. I was thinking some sort of relay for this but I'm unsure if I can get a relay that would work at such low currents/voltages (I haven't measured it in a while but I believe its on the order of a few hundred millivolts) and if this would mess up the audio signal. Unfortunately, the microphone is permanently attached and I don't think I'd be able to insert another wire into the mic cord to use as a 12v line for a relay. I'm looking for suggestions on what I could use for this situation.I have little acknowledge of relays:http://www.apogeeweb.net/article/65.html

Here is a quick diagram of what I'm looking to accomplish.



I am a system similar to this:

[TapeOpLarry]

I'm no EE, but you are going about this the wrong way. Obviously an external mixer, and a gate set to "duck" would be the best way to go. Or to wire in a new switch that also "tells" the music to turn off. But asking a relay to accept the "tiny" voltage of a microphone output to activate it is incorrect A relay is an on/off device, and this sort of operation would need to be done via a secondary circuit.

Sorry, I probably just made this all look a lot more difficult for you!

[suppositron]

Yes, Larry's totally right.

Relays expect their rated turn on voltage to switch. 3V, 5V, 12V, 24V... It depends on the relay but they expect a DC voltage to switch. You'd need some sort of peak detect circuit to drive the coil in the relay and switch when it crossed the threshold.

And I also agree a compressor that ducked the other source is probably a better option and would sound better than a hard switch.