I've been looking through a lot of forums on this topic and the inconsistency of people's suggestions is starting to freak me out. I have 32 tie lines starting off my bays full normalled to my 32 console pres and several more channels of outboard pres on the side, all capable of sending a death sentance to anything I might care to patch it to. I have essentially two concerns; 1: Do I need to get some sleeve normalling jacks in this thing (I currently have tip/ring normalling jacks in place and was planning to hard wire the sleeves, but if the sleeve isn't normalled, aren't I still returning 48VDC to the normalled console pre connector when only the tip and ring normals are opened by a patch)? and 2: Should I be worried about the brief moment a TT cable makes wrong connections as you make the patch before the plug seats to its correct connections if phantom power is accidentally left on and a hot patch is made? I've also heard that ground bussing is a good idea from some people and a bad idea from others so i gotta wonder who's right on that one too. All in all, I just become more confused about how to safely introduce phantom into the bay with each new inquiry. I figure that Electrical has had phantom in the bays forever and probably doesn't end up with a dead mic or piece of gear everytime somebody forgets to turn phantom off and/or patches to the wrong place (or maybe the danger of killing your mic collection just keeps it interesting... some sort of fun challenge?), so how's your stuff wired?

LaserMoney wrote:I've been looking through a lot of forums on this topic and the inconsistency of people's suggestions is starting to freak me out. I have 32 tie lines starting off my bays full normalled to my 32 console pres and several more channels of outboard pres on the side, all capable of sending a death sentance to anything I might care to patch it to. I have essentially two concerns; 1: Do I need to get some sleeve normalling jacks in this thing (I currently have tip/ring normalling jacks in place and was planning to hard wire the sleeves, but if the sleeve isn't normalled, aren't I still returning 48VDC to the normalled console pre connector when only the tip and ring normals are opened by a patch)? and 2: Should I be worried about the brief moment a TT cable makes wrong connections as you make the patch before the plug seats to its correct connections if phantom power is accidentally left on and a hot patch is made? I've also heard that ground bussing is a good idea from some people and a bad idea from others so i gotta wonder who's right on that one too. All in all, I just become more confused about how to safely introduce phantom into the bay with each new inquiry. I figure that Electrical has had phantom in the bays forever and probably doesn't end up with a dead mic or piece of gear everytime somebody forgets to turn phantom off and/or patches to the wrong place (or maybe the danger of killing your mic collection just keeps it interesting... some sort of fun challenge?), so how's your stuff wired?

if you plug a condenser-microphone to one channel of your patch bay and that channel is plugged to one channel of your board, then you will get the phantom power from that channel of the board over the channel of the patchbay into your condensermic. the wiring is completely connected
mic will work.

...honestly, i didn't get your message. try to simplify your description...
thanks

I'm not really aware that hot-patching phantom power will destroy your mics, excepting ribbon mics. I'd be more worried about my speakers & cue system headphones & the ears that'd be centimeters away from said cue system headphones.

Sorry if I'm only contributing to the whole 'everyone here is giving different answers!' thing; this is just how I understand things to work. Just trying to help.

I think what Laser is worried about is the 48VDC getting into other outboard gear - If one was to patch that 48V riding on pin 2 and 3 into the input of a piece of outboard that has an IC or semiconductor directly in the input path, there is a chance you can fry something. Also, ribbon mics are a valid concern if the mic itself is wired incorrectly.

If you just run pins two and three two the bay, you will have no ground reference between the two, causing no voltage to show up at the bay inputs (both two and 3 have the 48V DC attached to them).

However, if you set up the bay correctly, you should only make that mistake due to "operator error". You probably want to have your sleeves intact on the bay at least for the normalling between your snake or wall plate and the inputs on the console. If the direct outs/buss outs on the console are unbalanced, then you could continue without sleeves on the bay.

Honestly, the best way to avoid accidents are to not make the mistake in the first place - I highly doubt a brief (under 1/2 second) exposure to 48V will fry the input of anything, but I do understand your concerns as gear is super-expensive. Also, keep in mind that if you don't actually plug the whole patch connector in, it is doutbful you will be able to complete the circuit in order to generate 48V into the input of a device.

Oh yeah, I'm not familiar with the term "ground bussing" - could you elaborate a bit more?

Jordan

I don't know if posting a reply is the best way to elaborate on my own topic, so if there is an etiquette to this (as you can see, i'm still a troll) someone please inform me. ok so...

To start, Jordan asked about ground bussing which is just a term for connecting all the grounds together - what I'm wondering is if i should "bus" all of my grounds together at the tie lines and/or mic pres for the sake of phantom power. I have been told both to do this and not to... I'm thinking not, as I've also heard that you should use patchbay jacks with ground normalling (aka ground switching) which have a sleeve normal as well as tip and ring normal tabs; this way the sleeve is normally connected, and is disconnected when a patch is made. Without this, I would have to hard wire the sleeve from the tie line's patchbay jack to the console pre's patchbay jack or phantom power would never make the trip (since the sleeve carries the ground reference for the +48VDC). My concern is that if I am using an outboard pre patched into a tie line that is normalled to a console pre, only the tip and ring will be disconnected from the console pre due to full normalling, so my sleeve will be shorted between my outboard pre and my console pre (provided i have hard wired the sleeves rather than found and used sleeve normalling patchbay jacks)... So, if this happens: What will happen to my pre's if phantom is on in one, and what if it's on in both?

My second concern is for the mics. I understand that, with the exception of some models of ribbon mics, phantom power will not hurt my mics when wired correctly. This is exactly the problem - when making a hot patch (phantom on while patching), which is indeed an operator error (but an error that has and will be made, even by seasoned veterans of the game), or any patch for that matter, the mics are not wired correctly for a brief moment. If you'll humor me, visualize this with me in slow motion: When a patch is made, the tip (hot/+) first touches the sleeve (gnd) of the jack as it enters the hole; next, the ring (cold/-) enters and also shorts to the sleeve, now all three terminals are shorted together; then, the tip comes out the other side of the jack's sleeve/hole, leaving the ring and sleeve still briefly shorted, then maybe hits the ring's tab (+ sent where - is expected) on the way to its own tab where all the connections are now in place and phantom is being properly delivered to the mic. Now I know all of this happens in less than a second but I've seen caps explode, mosfets explode, soldering iron tips explode shooting little 700 degree shrapnel into my face, and a tech thrown from his desk on to mine; and each in under a second. Of course, we're talking 48VDC here, milliamps. No one is going to die. But what could happen to my poor little sensitive, way to damn expensive mic?

Please excuse the length of my dilemma, and thank you for any help or insight anyone can offer,
Nelson

anybody else got 2 cents I could borrow?

Just to clarify, I think it sounds like you've got your microphone XLR breakout box(es) wired into the top row of a fully normalled bay, the bottom row goes directly to your console pres, and you can patch from the top row into the mic inputs of your outboard preamps. You're probably never going to be patching from the top row into the inputs of line level effects, or the outputs of line level effects into your bottom row, right? That is, you're not going to be patching line level stuff into the path between a microphone and a mic pre, and you probably won't send a line level signal back into your console's mic preamps -- for that you'll use a line input instead, right?

Since you know this bay is only going to be used for mic outputs and mic preamp inputs it does simplify things. It's not like you're going to be momentarily patching phantom power to an unbalanced input with a 16 volt capacitor, which could legitimately be bad.

The main thing you should do is just always patch in the correct order. Plug your patch cord into your mic first (breaking the console connection) and then plug into your preamp second.

Obviously sometimes we don't do it the right way, and I know those are the times you're really worried about, but don't worry TOO much.

Your preamp inputs are all going to be able to take 48 volts static at the input. Transformers can handle this much, obviously, and since you're only patching into mic pres, they mostly all SHOULD have 50 or 63 volt input blocking caps.

The only potential conern is that current can flow from the 48 volt source down through the un-charged preamp input to ground (and this will probably all be referenced together even if the sleeve's aren't connected. It will probably all be real earth ground no matter whether it's a outboard pre or your console that's supplying the 48 volts). With electronically balanced inputs this isn't an problem at all, since the only pathway to ground will be through a pair of 6.8K resistors, so less than 4mA will flow, and for just an instant. That's not enough to cause problems (other than audio popping).

Transformer balanced inputs have more trouble because some or all of that current may flow through the transformer primary in an unbalanced way. Current's limited by the 6.8k resistor, so probably not enough current can ever flow to actually break the primary, but it could put a bit of magnetism on the core. The good news is that when phantom is turned off, most transformer input pres let the primary float rather than keeping a reference to ground, so no current can flow unless the other side is grounded through your patch bay, which should never happen in this setup.

Some transformer input mic pres have a ground reference though the center tap, or have a bleeder resistor from the junction of two 6.8k resistors to ground, but usually the total resistance is higher than just the normal phantom resistance, so it will limit current further still. But in order to be careful and safe in every situation, all you really have to do is just patch in the correct order.


I don't really think using a patch bay with ground switching will really be an appreciable advantage. For one thing, the tip of your patch cord will still hit the sleeve of the patchbay jack before anything else happens or anything has a chance to switch, so you don't really eliminate that problem, and as far as keeping the phantom ground references seperate...it's hopeless. They'll all end up in the same place anyway. You might eliminate a potential source of ground loops, but you won't eliminate a current path.


Ned

For your mic input patch bay, the 2 rows should be normaled ("mic line 1" to "mic input 1"). If you patch into either point the normal should break completely (tip, ring, and sleeve). There should be no ground connecting through from "mic line 1" to "mic input 1" when a patch cord is connected to either. If you have a patch bay that does this, replace it. Having the shield continue through to the console preamp, with the external preamp connected, will give you a nice ground loop at the most sensitive point in your studio's signal path.
Assuming your mic cables and wiring is correctly built- Ribbon mics are fine with phantom power as long as they are connected properly when it's turned on. Don't unplug xlr or patch point while phantom power is on. A split-second voltage can appear across the two output windings of a ribbon mic's transformer, energizing the magnet, then driving the ribbon. This happens on occasion, and wont typically destroy the mic.

Greg, where would one find tt jacks that have sleeve normalling? I'm having a hell of a time tracking such a thing down. I've read about sleeve normalling here and there, but can't seem to find a part number.