Cans over EDAC multicore

[Freddie]

Yes! It's me again! We're starting to think about what we're hiring for our BIG show in a few months and we're (Fingers crossed, depending on the budget) having cans. Rather than hiring long XLRs to connect wings to back of hall, can we run them over spare XLR channels of our EDAC (Multicore)?

[Brian]

Yes, although if you're running any unbalanced circuits down the multi (=bad idea anyway) you may get a click when the call button is pressed.

[Freddie]

Ta muchly Sir Fairchild

[mackerr]

Yes, although if you're running any unbalanced circuits down the multi (=bad idea anyway) you may get a click when the call button is pressed.

<{POST_SNAPBACK}>

:D You most likely will be running unbalance circuits down the multi once you have your comms in it. Most (not all) comms systems have unbalanced audio in the 3 pin part of the system. Here in the US the only balanced system is Telex Audiocom, and I believe there is also a balanced system in the UK, but I am unfamiliar with it. If you have a seperate multi for high level returns, that might be a better place than your mic mutli to run comms. If you have a 2 channel system that runs both channels on a single 3 pin circuit, you have 2 unbalanced signals in 1 wire. These runs should be kept to a minimum to reduce crosstalk between the channels.

 

Mac

[J Pearce]

In previous shows I have worked on we have sent comms down the multicore and had no problems. All our mic signals were balanced apart from the comms which have to be unbalanced to send 2 way down a 3pin.

[paulears]

I concur, I've run a Tecpro system like this for years, with no problems.

[Andrew C]

The only potential problems as I see it are;

1) As Brian says, possible 'clicks' as the call system is used, especially if unbalanced audio is present.

2) Care must be taken when plugging up to avoid DC being applied to kit that doesn't appreciate it.

[mackerr]

In previous shows I have worked on we have sent comms down the multicore and had no problems. All our mic signals were balanced apart from the comms which have to be unbalanced to send 2 way down a 3pin.

<{POST_SNAPBACK}>

Actually, comms don't have to be unbalanced. Telex Audiocom is a balanced system, but most systems are unbalanced. There is not a send and return on different wires, there is a common talk bus on 1 wire, power on another, and ground on pin 1. RTS, and Clear-Com TW type comms which have 2 channels on one 3 pin cable put the second talk channel on the same wire as power and then block the DC from the audio in the belt pack.

 

The suggestion to keep comms in a high level multi if possible is because most comms systems have a standard operating level of -10dBV to +4dBV, where microphones may be down around -30 to -50. For the sake of preventing any possible crosstalk it is a good idea to keep high level signal seperate if possible. That doesn't mean that there will be problems, only that it less likely in a high level multi.

 

Mac

[Darkfold]

Just do it :) Be careful of what goes into what socket tho, most desks do not appreciate a DC power supply being applied to a mic preamp accidentally.

[J Pearce]

I stand corrected. I had thought there were 2 buses, but actually it would make more sense to have one.

[mackerr]

Just do it :) Be careful of what goes into what socket tho, most desks do not appreciate a DC power supply being applied to a mic preamp accidentally.

<{POST_SNAPBACK}>

The fact that the DC voltage is on just one leg of the audio may make it a problem for the desk, I'll have to think more about that, but 24V-30V DC is definately less than the 48V that gets applied to that mic pre when you turn on the phontom power.

 

Mac

[paulears]

yep, but don't forget the phantom power is current limited whereas we're talking AMPS for powering multiple comms units - sticking that up the mic amp will almost certainly fry it!

[mackerr]

You're right there. I was wrongly assuming that the current limiting resistors were between the phantom supply and the mic, but they need to be between the phantom supply and the mic pre to connector link. The other way puts them between the mic and the mic pre. Oops.

 

Mac