Plumbing comms into a talkback system

[samchurchill]

Hi,

 

We’ve got a need for a talkback system that interfaces with our production comms system. Here’s a bit of background of what we’ve currently got:

 

* Band with an on-stage MD (normally playing keys) that has a dedicated talkback mic which is fed into all of the IEM channels so that all band members can hear the prompts.

* A completely separate comms loop with 4 stations

 

We’d like all members on the comms to be able to hear the MD’s talkback mic, which I think is fairly easily done using the comms base station’s aux input. However, this could be done another way if the next requirement means it’s more appropriate...

 

We want one of the comms users (DSM) to be able to talk back into the IEM channel of the MD, essentially allowing a 2-way conversation. Ideally this would be by pressing a switch and talking/listening through the existing comms headset.

 

This sort of thing must not be too rare in really big productions. Any ideas on what the best way to achieve it might be?

 

Would prefer off-the-shelf, but not scared of a bit of DIY and soldering either.

 

Thanks,

 

Sam

Edited October 8, 2019 by samchurchill

[mackerr]

Hi,

 

We’ve got a need for a talkback system that interfaces with our production comms system. Here’s a bit of background of what we’ve currently got:

 

* Band with an on-stage MD (normally playing keys) that has a dedicated talkback mic which is fed into all of the IEM channels so that all band members can hear the prompts.

* A completely separate comms loop with 4 stations

 

We’d like all members on the comms to be able to hear the MD’s talkback mic, which I think is fairly easily done using the comms base station’s aux input. However, this could be done another way if the next requirement means it’s more appropriate...

 

We want one of the comms users (DSM) to be able to talk back into the IEM channel of the MD, essentially allowing a 2-way conversation. Ideally this would be by pressing a switch and talking/listening through the existing comms headset.

 

This sort of thing must not be too rare in really big productions. Any ideas on what the best way to achieve it might be?

 

Would prefer off-the-shelf, but not scared of a bit of DIY and soldering either.

 

Thanks,

 

Sam

 

If the master station of the comms has both SA out and PGM in you're done. Use the SA (stage announce) out as a line level sent to the IEM system, and the PGM in as a listen to the musical director.

 

Mac

[samchurchill]

Ah, that makes sense, thanks. Will have a look at the base station this weekend - it’s installed in the venue we use and at the moment I don’t even know whether it had PGM, let alone SA.

 

Am I correct I’m assuming some sort of box between the headset and the base station is a non-starter?

[samchurchill]

So, it turns out that the venue’s comms main station doesn’t have either a pgm input or stage announce output :-( Has anyone got any thoughts on the idea of an interface box between the main station and the headset?

 

Thanks

[pmiller056]

You could make up a custom headset lead with isolation transformers (think of a DI Box) to get comms audio to wherever you need, although microphone sidetone into the headphones could be a problem for your application.

Alternatively you could make up a Bluecom PCB (look in the workshop thread) in an appropriate project box and plug it into the venue comms system. The Bluecom system is compatible (set audio levels appropriately) with most older partyline intercom systems. There is a pin header on the PCB with access to all the signals you need, however you will most likely need to add isolation transformers between the two audio systems to avoid hum problems. I'd prefer to do it this way so that there is no need to modify someone else's system and you can take it away with you after your show for the next time.

[timsabre]

The proper way to do it would be to use a tecpro 2 to 4 wire adaptor box, but they are not cheap.

 

https://www.canford.co.uk/Products/27-903_TECPRO-AD903-2-to-4-wire-adapter

 

[kgallen]

I must have misunderstod the requirement somewhere, and I'm sure Tim would have pointed to the Best Audio page, but as the AD903 is being mentioned now...

 

Does this circuit help at all? (Login needed now for the Best Audio site).

 

http://www.bestaudio...nly_adapter.pdf

 

(The full section on adapter circuits here: http://www.bestaudio.com/downloads)

 

Kevin

Edited October 16, 2019 by kgallen

[timsabre]

I must have misunderstod the requirement somewhere, and I'm sure Tim would have pointed to the Best Audio page, but as the AD903 is being mentioned now...

 

Does this circuit help at all? (Login needed now for the Best Audio site).

 

http://www.bestaudio...nly_adapter.pdf

 

(The full section on adapter circuits here: http://www.bestaudio.com/downloads)

 

Kevin

 

I think he wants sound both ways - which is what the 2 to 4 wire box does, it's basically a beltpack with the mic / phones signals broken out to isolating transformers with gain controls .So pretty much what PMiller said but a commercial version.

 

[samchurchill]

Thanks all, the AD903 looks ideal. I’ll also take a further look at those projects and weigh up whether I’ve got time to make them!

[samchurchill]

So, I decided to go down the route of getting a Tecpro AD903 and it's working well. Can someone check my working on the following please?

 

I want to make it so that someone near the AD903 can easily choose whether the comms feed is sent to the desk's input that feeds the IEM, rather than it being on all the time (which would distract the musicians). I'm I right that I can just insert a momentary push switch into the signal from pin 4 of the XLR4 socket? I realise that this will likely cause a bit of a pop when engaged, but that's not the end of the world and should be able to be reduced a little by keeping the AD903's output high and the desk's gain low.

 

Tecpro AD903 data sheet at https://www.canford.co.uk/ProductResources/resources/T/Tecpro/02-132%20Issue%204.pdf

 

Any thoughts?

 

Thanks, Sam

[henny]

you coud use the basis of a Tecpro call light to switch a relay so coms audio is only passed when when the call button is pressed

 

see http://www.blue-room.org.uk/index.php?showtopic=18840

[timsabre]

You can do that and some of the PMR/walkie talkie interfaces use call light to trigger TX mode, but it can quickly get confusing when people press it accidentally (which seems to happen a lot as people fumble for the mic switch).

A push switch in the signal path should work if local control is all that is needed.