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Old 23rd August 2012, 05:57 PM   #1
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Hey everyone...

I'm an electronics noob when it comes to designing gear, so please forgive the seemingly basic question.

How would you design a box that would need to route a dynamic microphone to two different outputs? One of them would be a main output for on-air use and would have a cough button/switch to kill the audio to that output, and a second output that would be to talk off-air when a button is pressed. That button would kill the main output and activate the second output?

The smaller, the better. The less components, the better. If it could be unpowered, or via 12VDC, that would be even better!

Size is an issue as I would ned to build 4 of these and travel them across the country. There's a company that builds these, but they are prohibitively expensive, way too large, and extremely heavy.

Anyone have any experience with this? Could someone help me out?!

Thanks!
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Old 25th August 2012, 04:17 AM   #2
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Is there a better place to put this topic? Forgive me if it's in the wrong spot...
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Old 25th August 2012, 10:31 AM   #3
AuroraB is offline AuroraB  Norway
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You'll most probably have to pre-amp the mic first, in order to avoid clicks or pops. Switching can then be done via a fairly simple swith, but an electronic switch, something like an SSM2402, will do a lot better.
If the mixer have an insert jack, you may be able to use this with a single switch, but then you'd need to open the fader for talk-back also, and possibly there will be click noises.
There are also a few very good single chip mic preamps too, in the SSM series from Analog Devices.
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Old 25th August 2012, 06:16 PM   #4
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Thanks for the reply...

It's funny you mentioned the insert, because I had been toying with that idea before you brought it up as a way to easily "mute" the on air audio and provide the line level audio for switching.

In the attached drawing, you'll notice a Rolls PS16 feeding an input to the device. The PS16 supplies 12VDC down the ring of a TRS, and the headphone signal down the tip to feed and supply the headphone amp with the necessary power and input. (This is a very slick setup as I often times have 4 headphone amps for the talent and crew and only need 1 wall wart in the back with the engineer.)

I haven't measured to make sure it's exactly 12VDC, but I'm fairly certain it's at least close.

So I would steal those 12V to power 2 SPDT relays, one to open the contacts that connect the tip to the ring of the insert from the mixer, which essentially "mute" the on-air audio, making this a cough switch. The other button would power both relays, again opening the loop muting the on air audio, and then connecting the tip to the talkback output on an XLR.

Does this look like it would work?

What advantages would electronic switches have over relays? Could the rest of the circuit remain the same, just replace the relays with those switches?

I'll look into the 2019 pre-amp, as ideally, I'd like to keep the inserts open. Would the 12VDC from the headphone amp circuitry give enough power to the pre, allowing me to do the switching pop-free? How would you design that circuit?
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Old 25th August 2012, 10:00 PM   #5
AuroraB is offline AuroraB  Norway
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In principle that should work, and the relays could be replaced with the SSM switches, provided you adhere to the extra resistors shown in the SSM datasheet.
Relays would probably give click noises, as I assume the insert point have coupling capacitors both in and out. Notice that the SSM2402 are not brute force switches, but uses FET transistors that are ramped on-off, thus eliminating the clicks.
The drawback is that these need +/- 15V supply and a separate logic control voltage.
the +/- supply can possibly be 'stolen' within the mixer, and the logic control voltage either by regulating or at least filtering a separate line off the positive supply line.
Notice that the 2402 has appx 10ms switching time, and the 2412 has around 3-3.5ms.
Just study the datasheet carefully, so you really understand how it works....

http://www.analog.com/static/importe...M2402_2412.pdf

EDIT: which mixer are you using?? Analog or digital?
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Last edited by AuroraB; 25th August 2012 at 10:02 PM.
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Old 25th August 2012, 10:17 PM   #6
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I'm using an analog mixer, either a Behringer 16 channel model (can't remember the model number, but it's a stop gap until I get get a better one), or a Mackie 1642.

I've been looking at the datasheet for the 2402, and I'm not sure I understand what I would need to do to get it to work. A lot of that goes over my head...

Trying to add more voltages into the box would make this fairly complicated, as I don't really want to have to add wall-warts, extra cabling, etc.

I wondered if the relays would cause an issue, but I was going to try to test it out when I have some time (still have to order the relays).

Are there any other options without adding more voltages? Or would I have to start all over and redesign the whole thing?
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Old 25th August 2012, 10:31 PM   #7
AuroraB is offline AuroraB  Norway
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Just try it with the relays then... if it makes pops, try some small resistors in series - 50-100 ohms or so...
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Old 26th August 2012, 12:27 AM   #8
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I'll see what happens with the relays. However, in the meantime, my only reasoning for keeping 12VDC is that's what the PS16 kicks out.

What would I have to change to make this circuit kick out 15VDC instead of 12VDC?

http://www.rolls.com/pdf/M_PS16.pdf

If I could get that to 15 volts, then maybe I could use the switches. I could then create a little voltage divider circuit for the logic control, correct?

Btw, the output feeds these:

http://www.rolls.com/pdf/M_PM50s.pdf

Thanks!
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