Topic: Protecting Soundboard from Phantom

[eman]

I had just ordered some patch cables to use the patchbay on the Soundcraft board at my local theater. Would it be possible to splice in a diode or remove a wire in order to avoid the possibility of feeding phantom power into the board? I plan to plug into my UA5 and however unlikely it would be for that to accidentally turn on, it could conceivably happen.

I'm also curious is there anything else I need to do- the patch TRS is send-return-ground, so I wouldn't think it would matter that the return gets connected to one of the balanced signal inputs on the UA5. It seems like that phantom power pin probably doesn't even connect to anything anyway.

If I add an xlr female to 1/4 female TRS adapter, then presumably I'd want to break the connection to the return so that a mono 1/4" plug would not short the return to ground, or is that more than necessary? The cables I already ordered are Bantam TRS to XLR male.

[DigiGal]

You should be able to block it out with a dc blocking capacitor in series with pins 2|3.  However, I'd recommend picking up a set of commercial inline phantom power blockers to ease the mind of the folks you will be patching with.

There are others but here's one option: Sescom SES-IL-PPB XLR Inline Phantom Power Blocker

[eman]

That's a little pricey- probably just features the same thing you are suggesting?

Perhaps better to forgo the UA5 and adapt to the 1/4"
input and tape/glue that on with a warning not to plug the xlr's into phantom powered decks. If anybody has any input on Part B of my question.

[DigiGal]

The other commercial options are more expensive.  The folks you'll be patching with may not trust a home brew solution.

[eman]

I'm good friends with the FOH and he's smart enough to discuss this with me and appreciate the fact that I won't do anything stupid, as opposed to the usual attitude of why bother if it could possibly be dangerous. We can also test at the end of the day by plugging the cable into a phantom powered unit that's hot and see what we get at the Bantam end before plugging it into the board.

He's also interested in setting up for multitrack recording, which I would imagine could also have the same problem depending on the box.

[yousef]

FYI, the one time I accidentally sent phantom power from the UA-5 to a desk, it was the UA-5 that got fried...

[eman]

I was thinking to adapt down to 1/4" which would make it far less likely that anyone would be trying to plug into a phantom powered mic input, and I'd be using my iRiver or M10 direct. Again, presumably I'd end up with the same TRS config (send-return-gnd) as the original send- what happens when I plug a mono 1/4" into this? Does the short from R to G cause any trouble? If I didn't leave the cables at the theater I wouldn't have to worry about someone else using them.

From the FOH doing multi-track point of view, he'd either have to protect all of the sends or be extra sure he didn't turn on phantom power from his USB input box. Protecting all inputs could get pricey.

Thanks for the info, Jon. It would seem like the most conservative solution to put protection in the Bantam-XLR cables.

[yousef]

Hang on, are you actually getting your signal from an insert point - hence the "send, return, ground" labelling?

If so, you would want to connect the send and return together or else you'll be breaking the signal chain...

btw my UA-5/desk disaster involved a Busman modded UA-5 and (I think) one of those Behringer Eurodesk boards.

[andy_landy]

i would not expect insert points on the desk to have p48v on them, but check the channel block diagram for the desk in question.

the other way round, you really don't want to shove p48v in the insert points. you may or may not get away with it, depending on how robust the desk electronics are, but it strikes me as a recipe for disaster. don't do it.

[F.O.Bean]

Out of all the SBD I've ever patched out of, I have MAYBE need to boost the signal w a preamp maybe like twice ever. I think most sbd run hotter than he'll anyway. I would just bring enuf cables to go straight from SBD>recorder, but as always, YMMV!!!!

[eman]

Common practice (although not recommended) is to halfway insert the plug such that the tip engages the ring output, but the internal jack tip to ring connection is not lifted.

A proper tip to ring connection inside the plug is a more reliable solution.

OK, I see, lift the ring connection from the adapter contact (keeping the mono plug from shorting it to ground) and tie it to the tip (keeping the Send-Return loop intact which would be broken by inserting the plug into the patch point).

[Patrick]

A pair of these and you're set: http://www.amazon.com/Rapco-Horizon-ISOBLOX-Transformer-Isolation/dp/B003MLBEW2

[eman]

I think I'm tending towards adapting down to 1/4 plugs and not using my UA-5, and warning the FOH not to let anyone plug into any kind of phantom powered mic inputs. I don't feel the need to spend that $75. Maybe at some point I will buy some isolators or add the DIY components to the cables.

Also, I think based on the comments about breaking the insert would mean that using the patch points would actually kill the channel in the mix unless the tip and ring were connected in the patch cable. I'm thinking we are going to end up doing some creative routing to avoid using anything directly from the mix but for the multi-track project he's going to have to either just be careful about keeping phantom off (or disconnecting it entirely), buying a box of isolaors, customizing all of his cables, and/or doing the partial insert that Jon described. We can also do some homework about whether these patch points are already protected internally.

[yousef]

"I think I'm tending towards adapting down to 1/4 plugs and not using my UA-5, and warning the FOH not to let anyone plug into any kind of phantom powered mic inputs. "

Is anyone else completely confused by all this?

If you're thinking of using the UA-5, presumably you're just getting a stereo feed from the desk - ie from the stereo/tape out: usually a pair of 1/4" or RCA outputs. If you're super scared of sending phantom to these outputs from the UA-5, you could always plug them into the RCA-inputs on the back of the UA-5 - which has the added benefit of a greater degree of potential attenuation.

If you're doing a multitrack recording, it sounds like you'll be having to use the insert points on each channel so you'll need some doctored cables (TRS > whatever, with the tip and ring linked together) or do the dodgy "insert to one click" method. I'm not sure if you've mentioned what recording device you'll be using here but any fears about phantom power going awry would be solved by making sure that your recorder (or any mixer you have in front of it) does not have the phantom switched on.

In either case, you need not worry about what is going on in terms of phantom on the house desk.

Sorry if I'm stating the obvious but I'm really struggling to get understand what is going on here...

[kirk97132]

I had just ordered some patch cables to use the patchbay on the Soundcraft board at my local theater. Would it be possible to splice in a diode or remove a wire in order to avoid the possibility of feeding phantom power into the board? I plan to plug into my UA5 and however unlikely it would be for that to accidentally turn on, it could conceivably happen.

I'm also curious is there anything else I need to do- the patch TRS is send-return-ground, so I wouldn't think it would matter that the return gets connected to one of the balanced signal inputs on the UA5. It seems like that phantom power pin probably doesn't even connect to anything anyway.

If I add an xlr female to 1/4 female TRS adapter, then presumably I'd want to break the connection to the return so that a mono 1/4" plug would not short the return to ground, or is that more than necessary? The cables I already ordered are Bantam TRS to XLR male.

see a world of problems with your post.
1.) you say Bantam plug, do you mean the Bantam TT style which is what is comonly refered to when you say Bantam?  That is NOT a 1/4" plug it is 3/16"

2.) you never say where you are plugging into the sbd at.  IE: Aux send, direct out or insert to name a few.  They will all make a difference.

3.) you mention insert cables and then mention adapting it to XLR.  And keep refering to all trs as send return ground.  When that is ONLY true on an insert plug.  Otherwise the TRS is the same balanced connector as an XLR. 

Find out where you think you are plugging the cable into.  I suspect that you are not sure.  IF you are taking an output that is 1/4"  and is a TRS configuration then that is a balanced MONO signal.  There is not any send or return involved.  Stop thinking that TRS means send and return.  I really doubt that you are going to being using an true insert jacks to do a stereo recording of any kind.  And if by some off chance you are considering taking the insert feed off of a main send I would doubt any FOH engineer is going to let you plug in directly in front of his feed to the PA just because of the risk of something happening and losing his PA during the show.  I know I would NEVER let you plug into my signal chain at that point when I mix.  The "insert to the first click" is a last ditch when all else fails and again, if I am running sound you'r not gonna do it just because of the fact it is not a real connection just a half assed one.  If you are Multitracking (which you are not if you use a sony M-10) then you are going to want the direct outs.  And or be running snake splitters hopefully with transformer isolation.    IF you are just getting an aux send feed then you will need two.  That TRS feed from a send is a MONO balanced feed.  Yes it is the same style plug that a stereo headphone uses but it is a MONO signal.  Until you can tell us where youare plugging into the sbd then all of the talk about dropping the ring or combining the tip does not matter and in fact could screw you up.  To finish, ever SBD I have ever used can handle phantom power being accidentally introduced on a signal output.  Soundcraft, Yamaha, Allen & Heath, Roland, Tapco, Mackie, Presounus, even Behringer.  ANd I have plugged phantom into all of them accidentally with no ill effects.  It is some kind of common misnomer that just cause you see 48v pahntom that you are gonna burn something up.  Like Jon said that's not quite how it works