Injecting tecpro comms into desk

[dirkenstein]

Hi Everyone,

 

I'd like to be able to inject tecpro audio into a sound desk (on an aux return with pfl or similar) , so I can monitor talkback comms without forever swapping headphones.

 

Is there a safe, cheap way to do it without using a tecpro AD903 converter?

 

Just running the live bus straight into the desk with an adapter cable (which obviously doesn't pass the 24v power line on pin 2) seems a bad idea given the high(ish) signal voltage (12V?) used on the tecpro audio bus. Would a 1u capacitor provide sufficient isolation? Or just using a passive DI box?

 

Thanks,

 

Dirk

[smalljoshua]

How about splitting the signal after the Beltpack? Take the 2 pins on the 4 Pin connector that feed the headphones and feed them into the desk?

 

Josh

[dirkenstein]

How about splitting the signal after the Beltpack? Take the 2 pins on the 4 Pin connector that feed the headphones and feed them into the desk?

 

Josh

D'oh that is indeed the simplest way to do it. Make an XLR 4 to 2x XLR3 cable...

[mac.calder]

Drop pin 2 on the three-pin coms cable for clearcom and newer RTS coms and drop pin 3 on RTS's older style coms. Pin one can be connected straight through, or it can be connected to the shell.

 

If you are wiring to TRS, pin 1 sleeve, then whichever pin you have not dropped, take it to tip.

[Stan Hope-Streeter]

<br />Hi Everyone, <br /><br />I'd like to be able to inject tecpro audio into a sound desk (on an aux return with pfl or similar) , so I can monitor talkback comms without forever swapping headphones.<br /><br />Is there a safe, cheap way to do it without using a tecpro AD903 converter? <br /><br />Just running the live bus straight into the desk with an adapter cable (which obviously doesn't pass the 24v power line on pin 2) seems a bad idea given the high(ish) signal voltage (12V?) used on the tecpro audio bus. Would a 1u capacitor provide sufficient isolation? Or just using a passive DI box? <br /><br />Thanks,<br /><br />Dirk<br /><br /><br /><br /><br /><br />

 

I use a rep coil (600 ohm 1:1 isolating transformer) with a 10 uF 100 V non-polarised blocking capacitor in series with each winding. This can be used either as a comms isolator, or as an audio pickup / inject. The circuit diagram can be found on the Best Audio website, look for "audio only for RTS". For Techpro or Clearcom you only need the single circuit version.

[Ynot]

Hmmm...

 

We did something like this here not so long back.

 

My preferred manner is to send an aux feed from the desk into the Tecpro master PSU - there's an AUX IN socket on the fromt and an input pot to boot.

B-)

[Stan Hope-Streeter]

<br />Hmmm...<br /><br />We did something like this here not so long back.<br /><br />My preferred manner is to send an aux feed from the desk into the Tecpro master PSU - there's an AUX IN socket on the fromt and an input pot to boot.<br /><img src="style_emoticons/default/smile.gif" style="vertical-align:middle" emoid="B-)" border="0" alt="smile.gif" /><br /><br /><br />

 

He wants to do it the other way round...

[mackerr]

I use a rep coil (600 ohm 1:1 isolating transformer) with a 10 uF 100 V non-polarised blocking capacitor in series with each winding. This can be used either as a comms isolator, or as an audio pickup / inject. The circuit diagram can be found on the Best Audio website, look for "audio only for RTS". For Techpro or Clearcom you only need the single circuit version.

 

I know I've posted this a least a couple of times before. Here is the link to the audio only box for Clear Com and RTS. What is channel 2 on RTS is channel 1 on Clear Com single channel packs. This will not provide any sidetone adjustment if you will be talking on comm as well as monitoring.

 

Mac

[Ynot]

He wants to do it the other way round...

yes, I know that. However, I was suggesting an alternative, and pointing out that this topic has been done here in another thread.

Also there is always the possibility of accidentally feeding any comms in signal to the house if taking it in to a desk input...

[Mixermend]

Dirk only wants to monitor what is happening on the 'comms - but via the mixing desk - so the AD903 with its hybrid transformer and both way facility isn't necessary for this application.

 

I would build a small box with male and female parallel connected XLR's so the comms cable could be intercepted and build the circuitry shown on the link mentioned above into it.

 

DC isolating capacitor to pin 3 then into the top of a 10K log pot (bottom of pot to pin 1) - feed wiper into primary of small 1:1 audio transformer (other end of primary to pin 1). The secondary side to pins 2 + 3 to a male XLR (or TRS jack socket perhaps - to avoid mis connection) - with only TIP and RING connected. This can be fed to any mixer or amplifier input - isolated and adjustable in level to suit any input.

 

The level adjustment also permits the use of a very small and inexpensive isolating transformer without any danger of saturation. Almost any transformer will be fine for this application - no need to buy a Sowter, Jensen or Llundahl.......

[AndyL]

Also there is always the possibility of accidentally feeding any comms in signal to the house if taking it in to a desk input...

Yes, and even a small amount of breakthrough to the PA / monitors / show relay can prove 'fatal' to ones career if the 'wrong' thing leaks out.... B-)

 

Might be better to create an outboard resistive mixer to combine the desk headphone out with the headphone output from the Tecpro beltpack.

 

If it were an RTS system there is an AUX in on the BP 325 beltpack for just this sort of purpose, but that isn't any help on a Tecpro system, sorry..

[Neil Hampson]

would a small switch-box not suffice.

 

1/4" stereo jack in from desk

4 pin XLR from comms pack.

Output one or the other direct to the comms headset.

send the comms audio and say, left channel desk via a double pole switch. the right audio channel can remain as desk output permenantly or you could break it with the switch. same with the mcrophone.

No risk of comms getting to the PA, no active components, there would be a little bit of balancing to do with the volume outputs between the desk phone output and the output of the comms pack, but thats easily sorted.

[paulears]

Any input could be switched to the main system or monitors, when it's not wanted - as in what the actor in the dressing room thinks about another. However, we have plenty of controls to stop that happening, so I can't see comms being much different - just don't push the buttons or raise a fader? I like to think the simple idea is by far the best, and I take headphone out from the 4 pin XLR and then connect the two cores to XLR pins 2 and 3, NOT using 1. Why? because tecpro are very picky as to multiple grounds - and using the audio system ground invites hum into the system, my way doesn't.

[dbuckley]

The TecPro intercom line ground is isolated from mains earth, and thus on a typical system is completely floating. Grounding it can cause interference breakthrough.

 

Pin 3 of the four pin headset connector is directly connected to the TecPro "ground".

 

Its always best to transformer isolate party line audio, and the el cheepiest transformer one can get is adequate, and certainly should coss less than a fiver, or $0 if you just rip apart an old transistor radio.

[dirkenstein]

The TecPro intercom line ground is isolated from mains earth, and thus on a typical system is completely floating. Grounding it can cause interference breakthrough.

 

Pin 3 of the four pin headset connector is directly connected to the TecPro "ground".

 

Its always best to transformer isolate party line audio, and the el cheepiest transformer one can get is adequate, and certainly should coss less than a fiver, or $0 if you just rip apart an old transistor radio.

 

Thanks for the suggestion- I thought there might be a good reason why a capacitor wouldn't be sufficient.

I may still use the idea, but put the isolator on the headphone out.

 

That information about grounding is also _very_ interesting.

I've heard some RF interference on our tecpro system so I'll be checking for unwanted ground connections now.

 

Possibly a cable with pin 1 shorted to shell somewhere, possibly our somewhat non-standard PSU...

 

In any case, I'm either thinking of feeding the signal into a separate heaphone amp with cue in rather than into the desk, and if I do feed it into the desk, I'll take quite serious precautions to prevent the usual cans banter from making it FOH....

 

Has that actually happened on anybody's show previously? Cans routed to FOH?

As an achievement, it sounds slightly beyond the usual level of finger trouble I've seen. I think it would seem to require either complete chaos followed by random button pressing/fader flicking/knob twiddling (the least effective problem solving strategy in my experience) or actually active malice rather than a technical fault or one-off twitchy fingers.