Implementing a talkover switch. - diyAudio
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Old 11th December 2011, 02:58 PM   #1
Trebla is offline Trebla  United Kingdom
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Default Implementing a talkover switch.

We have a basic Newmark 2 channel mixer for our Youth Club disco.
It doesn't have a "talkover" switch to make announcements, without turning the volume down.
Does anyone know how to implement one?
Sounds like its just a matter of temporarily muting the output by 14db or so.
Any ideas welcomed.
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Old 12th December 2011, 08:39 PM   #2
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Sorry, two channels being two stereo turntable/CDs? The attenuation in itself is not complicated; mixing the mic in could be more so.

Questions
1) Who is doing the announcements, the DJ or someone else?

2) What are you planning to use as a microphone preamplifier to get the mic up to sufficient level to drive the power amps?

3) From where do you need to do the switching? Right beside the mixer, or some distance away?

4) Are you intending to modify the mixer itself, or add an external box?

5) If the mixer has a microphone input, has it got an insert jack?

6) Do you have anyone experienced in electronic bodging?

The thing could end up just a passive box with a switch on it, or full of so many complications that buying a new mixer is a cheaper, simpler answer than the work (Oh, the work can be enjoyable, too; but you can't afford to make any mistakes you can't immediately backtrack on, which means not stealing power from your present mixer's supply, for one thing).
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Old 12th December 2011, 10:00 PM   #3
Trebla is offline Trebla  United Kingdom
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Hi chrispenycate.

Yep i can solder and follow diagrams. I build my own audio gear for home use.

This is a brand new basic 2 channel mixer for kids parties/discos.
It has its own mic pre-amp with 1/4 inch jack input.
Stereo inputs and outputs are via rca sockets.
It's not really a problem to move the sliders when using the mic, but i thought talkover buttons might be a nice addition.

I'd like the switches to be on the mixer panel, but haven't taken the cover off yet to see how much space there is inside. I suspect there won't be a problem.

If you know of a simple way of doing this then great. If it means using complex powered circuits then it's not important enough to warrant the effort.

Incidentally i used it tonight for the first time, with a laptop and CD player for sources. Works just fine.

Last edited by Trebla; 12th December 2011 at 10:04 PM.
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Old 13th December 2011, 07:50 PM   #4
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So, all the inputs go into the mix amps (mic and two lines)? So, if you reduce the gain of the mix amp, (easily done with a two pole switch) you also reduce the gain of the microphone. Since there are only two stereo inputs, you could put a four pole switch, with pads on each of the sources, but it's quite a bit more complicated than a straightforward dim switch. And more likely to introduce unreliability. They've obviously opted for a simple mixer, and a sophisticated operator. Where is the easiest place to pad it down is not really an electronic problem, but construction; if the RCAs and the pots are PC mounted, you could end up cuttin tracks on circuit boards, messy.

Unfortunately, the mix resistors are almost certainly mounted on the circuit board, or you could : find the mix amps (almost certainly virtual earth).
follow which mix resistors come from the mic, and which the line input.

All right, perhaps take that back; I went webhunting, and Google threw up a load of Numark consoles, which are, apparently, digital (for a couple of stereo sources and a mic? Isn't that a bit overkill?), and there adding a dim switch… not worth the effort. (Could be done with an external box in series with the inputs, but not elegantly)

Detach the two line input resistors from the line inputs from the left input mix node, and connect their loose ends together. Same thing on the right mix node. Put a series resistor roughly three times the value of one of the original resistors from each of the junctions to the mix point from which you have taken the resistors, and wire a normally closed two pole switch round the series resistors, so when the switch is not pressed the resistors are shorted out.
Is that clear? I've not managed to find a convenient way of posting diagrams on this site yet, and electronically it is ridiculously simple; it's finding the relevant components that's difficult. But that, if you can find them, is cheap and good quality, even if the circuit board's not quite as pretty (and easy to put back, later).

Last edited by chrispenycate; 13th December 2011 at 08:07 PM. Reason: Tried to find the mixer on the web.
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Old 14th December 2011, 06:11 PM   #5
Trebla is offline Trebla  United Kingdom
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Thanks.
I think i understand what you are telling me.

The mixer will be in use later this week, so it will be a few days before i can look at it.
I'll post further information at the weekend.
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Old 15th December 2011, 01:57 PM   #6
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Oh, no hurry; though I will soon be taking my annual holiday in the UK, so it might get pushed after the new year. No-one else

If you do open the thing up (to see available space) take a couple of photos of the interior, and pot them, give us an idea – surface mounting, traditional, digital?
Since nobody else seems interested in the problem (not enough of a technical challenge, perhaps; but anyone who has done performance knows that an ultra simple, well thought out mod can be a life-saver in live gigs) there's no real hurry; you can go on using it like that for a while.
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