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DIY Dynamic Microphone Switcher

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DIY Dynamic Microphone Switcher

Postby Dan LB » Sun Oct 01, 2017 4:41 pm

Hi all,

I'm looking to build a unit that will allow me to switch between two dynamic microphones connected to a single output for live use.

It would be used to switch between a microphone (Shure Beta 58a) at a standing position on stage to another Beta 58 at a seated position at a keyboard.

I was thinking of using a latching 4PDT footswitch in a box with 2 input XLRs and one output XLR and then use the 4th set of lugs on the switch to switch between two differnet coloured LEDs (probably powered by a PP3 battery).

Is the audio side of things as simple as just connecting it all up as is or can I expect to get nasty pops and bangs over the PA when switching if I do it like that? Phantom power will never be switched on for that channel on the console.

Any help would be very much appreciated.

Dan
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Re: DIY Dynamic Microphone Switcher

Postby Dan LB » Mon Oct 09, 2017 12:25 pm

Anyone got any thoughts on this?
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Re: DIY Dynamic Microphone Switcher

Postby blinddrew » Mon Oct 09, 2017 12:30 pm

My thoughts are that you should be ok as long as there's no phantom power. But I know less about things than you do so I wouldn't trust my opinion further than the length of this sentence...
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Re: DIY Dynamic Microphone Switcher

Postby Hugh Robjohns » Mon Oct 09, 2017 12:57 pm

The simple DPDT switch would do it, but there's a good chance they'll be some sort of thump at changeover time.

Ideally, you'd short the two output signal wires together to mute the signal, then switch the source, then un-mute... but in practice the simple four-wire switchover will probably work tolerably fine. Try it and see...

There are more elegant ways of doing it, but all require active electronics. Orchid electronics would be well placed to build a suitable custom device as he already has the basic technology required in other products.

Radial make the Gold-digger four-way mic selector too...

https://www.soundonsound.com/reviews/ra ... rry-picker

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Re: DIY Dynamic Microphone Switcher

Postby ef37a » Mon Oct 09, 2017 5:32 pm

If you are just switching 'AC' between mics and both lines there really should not be any thump or pop but I would load each mic with say 4k7 just in case.

The LEDs could be a source of noise so keep V and I as low as possible. Buy a 'lucky bag' of LEDs from Maplin and go through them with an R a battery and a meter. You should find a couple that give good light at under 1mA. (I found several, one was good at just 240.MICRO amps!) .Then power them from a Lithium 3V cell.

Phantom power: Not good if it did intrude. If cost and trouble is not an issue fit 22mfd at 63V in each line of the output XLR, don't forget tie down resistors to pin 1, 22k should serve.

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Re: DIY Dynamic Microphone Switcher

Postby Hugh Robjohns » Mon Oct 09, 2017 6:02 pm

ef37a wrote:If you are just switching 'AC' between mics and both lines there really should not be any thump or pop but I would load each mic with say 4k7 just in case.

The two mics will be picking up different things as they are spaced apart across the stage and thus the ambient low-end spill will be at different phases at the two mics. Consequently the average DC component of the AC voltage at each mic will be different, so when switching between them there will always be a thump or click, at least to some extent.

For that reason, a quick cross-fade (20-50ms) would be far preferable, but would obviously require active electronics...

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Re: DIY Dynamic Microphone Switcher

Postby ef37a » Mon Oct 09, 2017 7:48 pm

Hugh Robjohns wrote:
ef37a wrote:If you are just switching 'AC' between mics and both lines there really should not be any thump or pop but I would load each mic with say 4k7 just in case.

The two mics will be picking up different things as they are spaced apart across the stage and thus the ambient low-end spill will be at different phases at the two mics. Consequently the average DC component of the AC voltage at each mic will be different, so when switching between them there will always be a thump or click, at least to some extent.

For that reason, a quick cross-fade (20-50ms) would be far preferable, but would obviously require active electronics...

H

Well yes Hugh, bit of a noise under those conditions but maybe OP can flip during a silence?

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Re: DIY Dynamic Microphone Switcher

Postby Dan LB » Mon Oct 09, 2017 10:12 pm

Thanks all.

Hugh and Dave,,
unfortunately switching will be controlled only by the artist and with less than ideal sight-lines in some cases, so I'm relying on them. I think a call to John from Orchid (as I had almost presumed) might be the best way forward in this case.

I might just build the afforementioned unit anyway (for the sake of buying a 3pdt switch and see how it goes) but these will be big enough gigs catering for 2-5k people, so the PAs will be big enough. I'll let you know how the DIY approach works in rehearsals!

Dave, FYI I'm not that electronics savvy so I might hit you up for some detailed (simplified) explanations!! I'll give John from Orchid a call first though. :thumbup: I recently put in an order with him for DIs for this very project (and VERY good they are too!!)

Thank you all very much for your input.

Dan
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Re: DIY Dynamic Microphone Switcher

Postby Hugh Robjohns » Mon Oct 09, 2017 10:34 pm

Yes John will certainly be able to help. He already makes a single channel mic mute and the switcher you need could be built easily using a pair of mic mute circuits arranged so that when one is muted the other is open, and vice versa -- a very simple extension to the existing logic circuit he uses in the mic mute already.

Of course, another alternative might be to operate the FOH console remotely. Depending on the console, it might be possible to use a MIDI pedal, or even program patch changes on a keyboard for example, to operate the channel mutes (or mute groups) on the mixer...

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Re: DIY Dynamic Microphone Switcher

Postby Dan LB » Mon Oct 09, 2017 10:43 pm

Hugh Robjohns wrote:
Of course, another alternative might be to operate the FOH console remotely. Depending on the console, it might be possible to use a MIDI pedal, or even program patch changes on a keyboard for example, to operate the channel mutes (or mute groups) on the mixer...

H

Thanks Hugh,

Hadn't thought of that! Yes that might be a possibility! I'll bear it in mind!
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Re: DIY Dynamic Microphone Switcher

Postby ef37a » Tue Oct 10, 2017 7:48 am

Yes Dan, get in touch if you want. PM or mods have my permission to give you my email addy.

I can then scribble out a schematic and have a chat.

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Re: DIY Dynamic Microphone Switcher

Postby Mixedup » Tue Oct 10, 2017 9:18 am

Does it need to be an instant switch — as in, in the middle of a song when changing position — or just a quick switch, eg in between two songs?

You could use a dedicated device, and a switch might be more elegant... but you could use a small mixer with two mic channels. Leave the mics connected and use the channel mutes/solos or (if they're lacking) level faders/knobs to switch from one to the other, Then feed line from your mixer to FOH. A Mackie 402-VLZ4 comes in at about £99 street and much cheaper second hand, and I know these to sound decent.
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Re: DIY Dynamic Microphone Switcher

Postby Wonks » Tue Oct 10, 2017 6:30 pm

Or even just a single dual-gang balance-style pot that fades between the two mike signals (allowing to keep the pin 1 grounds common? The pot knob position will let you know which mic's selected, so no LEDs are required; and there's no risk of pops caused by switching. A high enough pot value should prevent any cross-talk between mics.
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Re: DIY Dynamic Microphone Switcher

Postby Dan LB » Thu Oct 12, 2017 10:44 pm

Mixedup wrote:Does it need to be an instant switch — as in, in the middle of a song when changing position — or just a quick switch, eg in between two songs?

You could use a dedicated device, and a switch might be more elegant... but you could use a small mixer with two mic channels. Leave the mics connected and use the channel mutes/solos or (if they're lacking) level faders/knobs to switch from one to the other, Then feed line from your mixer to FOH. A Mackie 402-VLZ4 comes in at about £99 street and much cheaper second hand, and I know these to sound decent.

It will only be used between songs. I'd like to keep it as simple as possible so a footswitch will be the best option i think.

Radial also make the HotShot ABi which should work but I still reckon I can make one for a lot cheaper (albeit sans the pad switches)

ef37a wrote:Yes Dan, get in touch if you want. PM or mods have my permission to give you my email addy.

I can then scribble out a schematic and have a chat.

Dave.

Thanks Dave PM sent :thumbup:

Wonks wrote:Or even just a single dual-gang balance-style pot that fades between the two mike signals (allowing to keep the pin 1 grounds common? The pot knob position will let you know which mic's selected, so no LEDs are required; and there's no risk of pops caused by switching. A high enough pot value should prevent any cross-talk between mics.

Nice idea Wonks, I'll look into it!

I've also emailed Orchid and am awaiting a reply.
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