Design Question About A Microphone Switcher Box

[Paul Marossy]

Anyone ever make a box that can send an XLR microphone to one of two outputs? I was initially thinking of just using a momentary type 3PDT switch (like a std bypass switch) but I am wondering if there would be popping noises in the PA if done that way. Would a relay system be better?

Help?

(The idea is to be able to use one mic and to switch between the PA or an in-ear monitor system, where only the musicians can hear what is being said in the microphone)

[alanlan]

It probably won't be noiseless but shouldn't be so bad as mic inputs are generally fairly low impedance and there shouldn't be much DC flying around, however if you're using +48V phantom power on one or either of your mic inputs it might be a different matter and might even be unhealthy for one or both of the inputs.

[harmonic]

Spargo on here put together exactly what you describe:
http://throneroompedals.com/still-small-voice-box

[Paul Marossy]

Spargo on here put together exactly what you describe:
http://throneroompedals.com/still-small-voice-box

Cool! So that uses a solid state relay?! I didn't know that such a device existed.

[harmonic]

Hmm ... not sure about that. If it helps, I used this relay:
http://uk.farnell.com/jsp/search/productdetail.jsp?sku=9949852

[Processaurus]

 There is some odd grounding on his schematic, C3 and R5 are shorted out, and the ground on XLR output A (because B is used for phantom power) should go to the ground lift switch.  Pin 4 on the XLR's shouldn't be connected except to the ground of the output without the ground lift, that is just the chassis ground.  There is no need to have power filtering on the 9v in, but there should be a reverse biased diode across the coil.

[spargo]

Interesting how when I was designing this I asked for input on the forum and didn't get much of anything helpful... So, better late than never.  Thanks for the input Processaurus.

The power filtering can simply be left out at your discretion.  As for the grounding - perhaps it's not perfect, but I can assure you one thing.  It does work pop-free with dynamic and phantom powered mics without any issues thus far, and it has been tested on multiple systems and microphones.

[spargo]

Spargo on here put together exactly what you describe:
http://throneroompedals.com/still-small-voice-box

Cool! So that uses a solid state relay?! I didn't know that such a device existed.

The relay used (Mouser #653-G5V-2-H1-DC9) is an electromechanical switch.  It is just like a stomp switch, but instead fired by applying voltage to it.  A momentary 3PDT would do the same thing, but the reason for going the relay route (as described in the article) is that I wasn't able to locate any momentary 3PDT switches I was satisfied with.  I instead went with the relay and the soft-touch momentary SPST switches from Smallbear, which are VERY nice.  That way it just requires a soft touch - you wouldn't want to miss the switch due to not enough pressure in a live setting.  

[Paul Marossy]

The relay used (Mouser #653-G5V-2-H1-DC9) is an electromechanical switch.  It is just like a stomp switch, but instead fired by applying voltage to it.  A momentary 3PDT would do the same thing, but the reason for going the relay route (as described in the article) is that I wasn't able to locate any momentary 3PDT switches I was satisfied with.  I instead went with the relay and the soft-touch momentary SPST switches from Smallbear, which are VERY nice.  That way it just requires a soft touch - you wouldn't want to miss the switch due to not enough pressure in a live setting.  

Oh, I see. It looked like an IC chip on the schematic!

I was thinking that a relay might be better because it can typically switch much faster and with less noise than a simple mechanical switch can.

[spargo]

The relay has the same size and pinout of a 16 pin IC, so the schematic uses the same icon. I'd stick it in a 16 pin socket for easy replacement if necessary.

[Paul Marossy]

The relay has the same size and pinout of a 16 pin IC, so the schematic uses the same icon. I'd stick it in a 16 pin socket for easy replacement if necessary.

Oh wow, that's small!

[Paul Marossy]

BTW, the reason I want to build a gadget like what you designed is because one of the worship leaders at the church I play at asked me about it. There are many ocassions where it could come in handy!

We know some of the people from the House Of Prayer. Interesting conincidence...

[spargo]

BTW, the reason I want to build a gadget like what you designed is because one of the worship leaders at the church I play at asked me about it. There are many ocassions where it could come in handy!

We know some of the people from the House Of Prayer. Interesting conincidence...

This seems to be the most popular use... very handy to talk to a sound tech or a team with in-ears, especially in sets where there is an element of spontaneity.

[Paul Marossy]

This seems to be the most popular use... very handy to talk to a sound tech or a team with in-ears, especially in sets where there is an element of spontaneity.

Yeah, totally. There has been some days when we have four or five songs picked out and we didn't really do any of them. It might be either stuff "composed" on the spot or other songs we don't have charts for. They do the hand signal thing, but that's not always practical. So the mic mute/re-direct box could really help with that.

[spargo]

Yeah, totally. There has been some days when we have four or five songs picked out and we didn't really do any of them. It might be either stuff "composed" on the spot or other songs we don't have charts for. They do the hand signal thing, but that's not always practical. So the mic mute/re-direct box could really help with that.

Yes, very practical.  Assuming you're all skilled musicians you can communicate throughout a set without any previous knowledge of the songs, and make it look like you're a very well practiced band. 

[Paul Marossy]

Ha ha, and therein lies the challenge for some of us musicians!

[harmonic]

Also handy to let the 'words' person know when you're calling an audible! 

[Paul Marossy]

Also handy to let the 'words' person know when you're calling an audible! 

Yeah, also a good point. Usually the guys in our A/V dept are right on top of it, though.