Canford tecpro outlets and wiring

[torch1972]

;) I am having trouble wiring up some wall mounted XLR Tecpro headset outlets two circuits A and B.....

 

This how I have tried to wire to outlets.... From the master station 2 female XLR(one for circuit) using 2 core and screen to the first outlet (each outlet has two male box mounted XLRs) from outlet to outlet I am using Starquad pro grade microphone cable (4 core and screen)

 

I have wired the XLR as Balanced Audio (3 pole XLR):

Pin 1: Ground / Screen

Pin 2: In phase / +ve / Hot

Pin 3: Out of phase / -ve / Cold

 

My problem is as follows....

 

On the first box circuit A is working but circuit B is ear piece volume is very low and when I turn it up the volume I get feedback.

on the rest of the boxes (7 of them) on circiut A doesn't work and circuit B I get feedback.

 

Have I wired the wall mounted boxes wrong? Does it have something to do with both circuits sharing the screen?

 

Any help would be great I look of the caniford website and it tells you about the headsets and belts but not how to wire a circuit.

[Brian]

How have you allocated the cores in the Starquad?

[paulears]

If I read you correctly, you have terminated the starquad at the master station end in two 3 pin XLRs, one for circuit A the other for circuit B? If so if you remove A altogether, leaving just B - does this one then work normally? Could you have swapped polarity on any of the B outlets. Disconnect all bar one and see if you get it working properly from the master station - disconnect it and try each outstation socket, if one doesn't work - maybe that is where the wiring got swapped.

 

The reality is it has to be either partial shorts in the B ring, swapped polarity or a partial link between A and B - Canford wiring is very simple - 1 to 1, 2 to 2 etc. The shared ground is fine - it's common to see 6 to 3 pin y splits, so I'd suspect a dodgy connection somewhere.

[boatman]

It sounds as though you haven't commoned pins 1 on the two wall outlets, so circuit B doesn't have a ground. Also you need to draw a circuit diagram of how you have daisy chained the wall outlets.

[mackerr]

Your description of your wiring is very unclear. You must maintain two circuits for each outlet box that has an A and a B 3 pin XLR output in it. You should not use Starquad for intercom runs of any length, it has too much capacitance for use with intercom systems. Standard shielded twisted pair, or individually shielded multipair cable is the way to go. Standard audio wiring with shield on pin 1, hot on 2 and cold on 3 is the proper sequence, although that terminology doesn't apply to intercom which is unbalanced audio on pin 3, power on pin 2, and the return for both on pin 1.

 

Mac

[paulears]

The Canford Audio Tecpro twin circuit cables use starquad?

[mackerr]

The Canford Audio Tecpro twin circuit cables use starquad?

I'm not at all familiar with Canford, but I assume it uses the same technology as Clear Com, Production Intercom, RTS and all the other unbalanced systems. Because they all involve common talk buses they all involve a kind of hybrid in the belt pack to separate the talk and listen audio off the talk bus. These circuits can be sensitive to capacitance. In a full hybrid R, L, and C, are what you adjust to achieve a good null. High capacitance cable can make it impossible to achieve the null that the system needs to stay out of feedback.

 

Mac

[paulears]

Oddly, the Canford ones, so common over here, are the same - but the only thing the manufacturer really makes plain is the cross-sectional area of the cable for power considerations. I suspect that the system was designed with their own product range of cables in mind - their BBC spec quad has always been pretty stable with them.

[torch1972]

How have you allocated the cores in the Starquad?

 

yes I have allocated the cores

 

A concurrent post has been automatically merged from this point on.

 

If so if you remove A altogether, leaving just B - does this one then work normally?

 

Could you have swapped polarity on any of the B outlets. Disconnect all bar one and see if you get it working properly from the master station - disconnect it and try each outstation socket, if one doesn't work - maybe that is where the wiring got swapped.

 

The reality is it has to be either partial shorts in the B ring, swapped polarity or a partial link between A and B - Canford (no 'I') wiring is very simple - 1 to 1, 2 to 2 etc. The shared ground is fine - it's common to see 6 to 3 pin y splits, so I'd suspect a dodgy connection somewhere.

 

I have removed A and B still doesn't work.

 

The general feedback I am getting is that I need to check I have not swap polarity and that all my connections are good.

 

 

thanks

[iamchristuffin]

How have you allocated the cores in the Starquad?

 

yes I have allocated the cores

 

 

 

Brian asked how you have allocated the cores, not if you have!

[dbuckley]

Sounds like circuit B could be unterminated, you do have a dual channel master station, yes...? And common grounding? And using one common power supply line for both the A and B circuits?

 

StarQuad is OK, and is what most manufacturers seem to use, I have some genuine Telex cables dual channel cables which are starquad.

[mackerr]

StarQuad is OK, and is what most manufacturers seem to use, I have some genuine Telex cables dual channel cables which are starquad.

Telex AudioCom is a balanced system and may be less prone to the instability caused by higher capacitance. Starquad type cable is specifically not recommended by every intercom specialist I know. I am not familiar with the Telex cables, but as far as I know, there is no other manufacturer here in the US using that type of cable. I was first alerted to this issue many years ago by Dave Brand, then an engineer for RTS, who has since had engineering positions at both Clear Com and Reidel. He reiterated the point just last year when we were both on a panel about intercom at the NYC AES convention. I have also been told the same by Pete Erskine, who chaired that panel, and is currently in Bejing overseeing the intercom for the opening and closing ceremonies of the Olympics.

 

Common practices aren't necessarily good practices, and just because something usually works doesn't mean it always works. Mic cable usually works for DMX, but I don't think you'll find many manufacturers recommending it, nor pros using it.

 

Mac

[boatman]

Well, so far we've had a lot of speculation, but the OP still hasn't come back and told us anything useful.

 

Here's a hint list for the OP:

 

1. Which master station do you have?

 

2. Which beltpacks are you using?

 

3. Have you drawn a diagram to show how you wired the first wall plate?

 

4. Have you drawn a diagram of how you daisy-chained the remaining wall plates?

 

Once we have the answers to these questions we might be able to offer the OP some positive help. Until then it's just guesswork.

[dbuckley]

Starquad type cable is specifically not recommended by every intercom specialist I know.

Interesting.

 

All I can relate is my personal experience, and at the scale of systems I have worked with (a couple dozen stations max). I haven't had the call to do the Olympics yet, but if I do get that call, I'll certainly be seeking the advice of experts in the field. I've run the math, and certainly at a few hundred meters of starquad cable, crosstalk starts to be significant, though how much of a problem that is depends on many factors.

 

Is there a decent recommended cable for two circuit intercoms? a pair of single cores individually screened with a decent size power core and a decent drain would be ideal, is such a cable known and used? What do ClearCom et al use for their two channel beltpacks?

 

Common practices aren't necessarily good practices, and just because something usually works doesn't mean it always works. Mic cable usually works for DMX, but I don't think you'll find many manufacturers recommending it, nor pros using it.

Although I hear you I disagree; multitudinous "pros" seem happy to use mic cable for DMX512, and I certainly saw a lot of DMX512 over mic cables when I lived in the UK. Now here in NZ you can't hire DMX512 cables made from anything other than mic cable locally from the pro hire establishments, I (an amateur!!) may have the only genuine DMX512 cables in the southern hemisphere. Well, OK, maybe thats a bit of an exaggeration, but you get my drift.

[mackerr]

Is there a decent recommended cable for two circuit intercoms? a pair of single cores individually screened with a decent size power core and a decent drain would be ideal, is such a cable known and used? What do ClearCom et al use for their two channel beltpacks?

Generally the channels are kept separate till they are within about 20' of the pack. From there a 20' 2 pair with 2 XLR3F on one end, and an XLR6M on the other. I am setting up a system like that at Carnegie Hall in NYC tomorrow.

 

Mac