How to test my comms system

[Amy Worrall]

I'm getting ready to go back to the theatre. Yey!

 

I've got an old dilapidated comms system that's been struggling for a bit. I need to test each part of it to find out what is fully working, what has issues, and what is dead.

 

Any suggestions on how to do this? I could just plug stuff in and find a friend who I can talk to, but I'd rather be more systematic. Test the PSU on its own, then test each belt pack, then test each headset.

 

If there's a way I could inject an audio signal from (e.g.) a computer into the line, I could use that to test combinations of belt pack/headset for receiving.

 

Any bright ideas?

 

Amy

 

[bruce]

I'd start off with PSU, make sure lights up properly.

 

Add 2 belt packs and headsets. Check that A can hear B, and B can hear A. Check call lights on each.

 

Add 3rd headset, test with 1st as above

 

Add 4th , test with 1st.....

[richardash1981]

I've got an old dilapidated comms system that's been struggling for a bit. I need to test each part of it to find out what is fully working, what has issues, and what is dead.

 

Any suggestions on how to do this? I could just plug stuff in and find a friend who I can talk to, but I'd rather be more systematic. Test the PSU on its own, then test each belt pack, then test each headset.

 

If there's a way I could inject an audio signal from (e.g.) a computer into the line, I could use that to test combinations of belt pack/headset for receiving.

Hopefully you know that the way most (all?) 3-pin XLR comms systems works is:- pin for common ground.- pin for DC power (often 24V).- pin for (unbalanced) audio.

The call lights are done via adding DC on the audio pin.

The belt packs then convert this to separate input and output audio lines which go to the headsets (these are generally passive, i.e. no electronics, but less reliable because of flexible leads etc.). Expect to spend a lot of time wiggling connections to find out which ones are intermittent!

 

The PSU will also have a load impedance (much lower than a beltpack) between the audio line and common ground, so that the belt packs see a more or less constant line impedance, no matter how many are in circuit. This makes it possible for the belt packs to control how much of yourself you hear back in your own headset (or leads to feedback!). There is often an adjustment for this somewhere).

You have 8 headsets and only 5 belt packs visible, so it sounds like trying to two belt packs working and then use those to test the headsets (as Bruce says), then carry on to belt packs.

You can inject / extract audio via the headset socket on a beltpack, but you generally need a couple of audio transformers (there are a number of threads on here about doing such an interface) and I wouldn't think it worthwhile for small amounts of kit. A portable radio you can drape one of the headsets round whilst you listen to the other end can be quite useful, because it's happy to talk all day and not be listened to!