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Phantom power not reliable through patchbay
Old 30th May 2009
  #1
Phantom power not reliable through patchbay

Ok, so lots of folks say that it's ok to run phantom power through a patch bay. So I figured it was fine. But I just spent a tortuous debugging session that got me to the conclusion that it's not working for me. The reason it was tortuous is that I just built the pre-amps (SCA) and just built an LA-2A, and so of course everything is suspect and something that was working fine before and now isn't was the very last thing to suspect. But eventually it came down to the fact that phantom power sometimes was working and sometimes not.

It's a TRS patch bay and everything is balanced. But I kept losing input and went through hell, pulling out the SCA enclosure and going through the tortuous procedure to open it up and re-test the pre-amps and they tested out good.

I eventually just yanked the whole patch bay and hooked up directly mic to pre to inputs and it worked fine every time. Put it back and sometimes it works, sometimes it doesn't. The sometimes part is what is wierd to me. And there were other wierd side effects today that mysteriously came and went, e.g. a significant reduction in input to the converters, and a lot of hum. Obviously I assumed those were also problems in my build, and wasted a lot of time trying to eroneously figure out what I'd done wrong.

So something is seriously wierd here but I'm not sure what it is. I REALLY need to have the inputs to the pre-amps patchable so that I can patch my DI to them when required, instead of the mics. If I have to bring the mics straight in, then I'm screwed on that front which would suck.

The only thing I can think of is that I didn't connect the ground connector on the back of the patch bay to anything. Could that possibly be related to it not reliably passing the phantom?

Hmmm... One thing that did change is that added more normalled patches, so that, by default, each mic input goes to a pre-amp which in turn goes to a converter. Whereas before things were mostly just manually patched all the time. So I wonder if that's it? Before, the only thing that was normalled was the mics going into the pre-amps by default (and therefore the phantom power signal), and nothing else was.

I'll go test that theory tomorrow. Oh, the tangled web (of cables) we weave.
Old 30th May 2009
  #2
I went ahead and tested it and that's not the problem either. I directly patched the mic to the pre-amp input. And I moved them over to a non-normalled one and directly patched it. In both cases, no phantom to the mic. Brought the mic input directly in and it works fine again.

So clearly this patchbay isn't passing phantom power, at least not from the SCA pre-amps. It worked fine before with the GR/P-1 pre-amps, so maybe there's some difference there, I dunno. I guess one difference before is that the GR/P-1 were in a lunchbox, not in a box screwed to the same rack and therefore probably sharing some chassing grounding through the rack rails maybe.

But that kind o' sucks because it means climbing behind the desk to patch in the DI when I want to DI something. Sigh....

Anybody have any thoughts?
Old 30th May 2009 | Show parent
  #3
No, passing phantom through the patchbay is a bad idea. If you want to DI something, use a DI box.
Old 30th May 2009 | Show parent
  #4
Lives for gear
 
nosebleedaudio's Avatar
It may be the ground is not making it thru...
What kind of TRS?
It's not a 1/4" longframe is it?
Old 30th May 2009
  #5
Gear Nut
 

Sounds like some kind of grounding issue to me as well, but if you really want your pre's in a patch, have you considered running a dedicated xlr patchbay for your pre inputs and then just run the outputs to the 1/4" bay so you can normal or half normal from there into the rest of your chain?
Then you can independently run phantom as well and not have to worry about it bleeding into other runs....
Old 30th May 2009 | Show parent
  #6
Quote:
Originally Posted by John Eppstein View Post
No, passing phantom through the patchbay is a bad idea. If you want to DI something, use a DI box.
Every time this comes up half the people say it's a horrible thing to do and the other half say it works perfect well and that it's done all the time in professional studios.

I have a DI, but it's a DI board that is designed to feed a pre-amp, so I need to be able to patch it into the pre-amps. Even lots of standalone DIs people want ot run thorugh a pre-amp for more mojo. So that's not a viable answer. I need to be able to patch into the pre-amp inputs.
Old 30th May 2009 | Show parent
  #7
I think I may just buy a small two channel phantom power box. I don't have rack space to spare for a separate XLR patch. I only have two mic inputs. So that would be inexpensive, keep the phantom power on the far side of the patch bay and just generally solve the problem.
Old 30th May 2009 | Show parent
  #8
Quote:
Originally Posted by nosebleedaudio View Post
It may be the ground is not making it thru...
What kind of TRS?
It's not a 1/4" longframe is it?
It's the Neutrik NYS-SPP-L1. The default configuration is for each channel to be independent with the ground going to the ground of the incoming connector. But it can be changed on a per-channel basis.

Neutrik - Audio - 1/4" Patch Panel - NYS-SPP-L1
Old 30th May 2009 | Show parent
  #9
Lives for gear
 
nosebleedaudio's Avatar
Quote:
Originally Posted by Dean Roddey View Post
It's the Neutrik NYS-SPP-L1. The default configuration is for each channel to be independent with the ground going to the ground of the incoming connector. But it can be changed on a per-channel basis.

Neutrik - Audio - 1/4" Patch Panel - NYS-SPP-L1
I would prefer the ground to be made via the patch cord, NO grounds bussed or connected to anything else except that pre...

It may be too late but the Audio Acc. 1/4" would be a very good bay for mic level..
It's a 1/4" longframe...

But more cheeseola also..
Old 30th May 2009 | Show parent
  #10
Quote:
Originally Posted by nosebleedaudio View Post
I would prefer the ground to be made via the patch cord, NO grounds bussed or connected to anything else except that pre...

It may be too late but the Audio Acc. 1/4" would be a very good bay for mic level..
It's a 1/4" longframe...

But more cheeseola also..
That's the way this one works by default and I didn't change that.
Old 30th May 2009 | Show parent
  #11
Lives for gear
 
Benmrx's Avatar
 

I wish I could help more. All I can tell you is that it is perfectly fine to run phantom through your patchbay. Practically every studio (except one) I've ever worked at or assisted in had all the mic lines and preamp inputs (along with EVERY OTHER possible input or output) on the patchbay. One of the most well known studios I've ever worked at had a Trident A-Range console where phantom was ALWAYS on, and everything was still up on the patchbay. Using ribbons in that particular room was a hassle, but other than that it was perfectly fine.

I know at my studio there was a bug that I noticed where phantom would only pass through if at least 1 hard patch was made from mic to preamp. Once that was noticed the more techy of the bunch fixed the problem and everythings been just fine ever since. These are using TT bays that we've wired ourselves (although I can't say I helped much in the soldering dept.......)

That being said, I used to have 1/4" TRS Neutrik bays here, and I never had a problem running phantom through the patchbay. Never used the SCA pre's though.
Old 30th May 2009 | Show parent
  #12
Yeh, it worked before, with the other pre-amps. So maybe it's just something different about the SCA pres or something. Also, as mentioned above, previously the pre-amp enclosure wouldn't have had any common case grounding with the patch bay, which is the case now. So maybe that's got something to do with it, I dunno.
Old 30th May 2009
  #13
Motown legend
 
Bob Olhsson's Avatar
 

Quote:
Originally Posted by Dean Roddey View Post
Ok, so lots of folks say that it's ok to run phantom power through a patch bay...
Been there, done that 40 years ago.

It's a REAL BAD idea...
Old 30th May 2009 | Show parent
  #14
The problem of course is that other people, who have perfectly working, professional studios say it's just fine and that it's been that way in many (well known) studios they've worked in. So clearly it's not a simple matter, and it's not some newbie greenhorn mistake.

But, whatever, it isn't working for me and I'll have to deal with it. I just ordered a two channel phantom power box. That'll sold my problems easily enough and cheaply enough.
Old 30th May 2009 | Show parent
  #15
Lives for gear
 
Teddy Ray's Avatar
 

Quote:
Originally Posted by Dean Roddey View Post
The problem of course is that other people, who have perfectly working, professional studios say it's just fine and that it's been that way in many (well known) studios they've worked in. So clearly it's not a simple matter, and it's not some newbie greenhorn mistake.

But, whatever, it isn't working for me and I'll have to deal with it. I just ordered a two channel phantom power box. That'll sold my problems easily enough and cheaply enough.
I am guessing that none of them are probably experienced as Mr. Ohlsson...
If he says it is a bad idea, you can pretty much take it to the bank.
Old 30th May 2009 | Show parent
  #16
Mr. Olsen's having worked at Motown doesn't make people have hallucinations of working patchbays that actually aren't working. Do a search here on Gearslutz about the subject and feel free to question the experience of those folks who say it should work fine and that it's done regularly in serious studios.

Geez... I knew someone was going to say that, and I was pre-annoyed.
Old 30th May 2009 | Show parent
  #17
Quote:
Originally Posted by Dean Roddey View Post
Every time this comes up half the people say it's a horrible thing to do and the other half say it works perfect well and that it's done all the time in professional studios.

I have a DI, but it's a DI board that is designed to feed a pre-amp, so I need to be able to patch it into the pre-amps. Even lots of standalone DIs people want ot run thorugh a pre-amp for more mojo. So that's not a viable answer. I need to be able to patch into the pre-amp inputs.
Well, yes, generally you run a DI box into a mic input - unless it's one of those "preamp-DI" things......

I had assumed from the post that were are talking about console preamps here (hence the difficulty of patching), not outboard. It should be noted that the inputs on a console are generally NOT suitable for use as DIs, as the impedance is too low and will load the typical magnetic pickup. A few outboard preamps (Avalon, etc) have proper HiZ inputs, but I don't see any problem patching into those.......
Old 30th May 2009 | Show parent
  #18
Quote:
Originally Posted by Dean Roddey View Post
Mr. Olsen's having worked at Motown doesn't make people have hallucinations of working patchbays that actually aren't working. Do a search here on Gearslutz about the subject and feel free to question the experience of those folks who say it should work fine and that it's done regularly in serious studios.

Geez... I knew someone was going to say that, and I was pre-annoyed.
It's generally considered bad practice to run phantom through a 1/4 inch (or TT) patchbay, as plugging in out out with the phantom active shorts out the phantom supply - not good......
Old 31st May 2009 | Show parent
  #19
Lives for gear
 
Teddy Ray's Avatar
 

Quote:
Originally Posted by Dean Roddey View Post
Mr. Olsen's having worked at Motown doesn't make people have hallucinations of working patchbays that actually aren't working. Do a search here on Gearslutz about the subject and feel free to question the experience of those folks who say it should work fine and that it's done regularly in serious studios.

Geez... I knew someone was going to say that, and I was pre-annoyed.

Man, you have no respect for the the old guard. Hopefully, you will learn some humility. Maybe it is me that is weird, but coming up in the Army(and south), ..I really cringe when I see disrespect being shown to the elder statesmen.. and it is OLHSSON.
Old 31st May 2009 | Show parent
  #20
Lives for gear
 
Teddy Ray's Avatar
 

Quote:
Originally Posted by John Eppstein View Post
It's generally considered bad practice to run phantom through a 1/4 inch (or TT) patchbay, as plugging in out out with the phantom active shorts out the phantom supply - not good......

Yessir.....but he says it is fine.. let him do it.
Old 31st May 2009 | Show parent
  #21
It's got nothing to do with respect. Clearly a lot of people disagree with him, and they aren't idiots. My problem is that he makes a lot of oracular statements that are clearly more his opinion than fact, and then anyone who questions him inevitably gets the "But it's Bob Ohlson" thing.

I respect the work he did at Motown, but that doesn't make him automatically right. It's been shown more times than I care to even think about how many times people in the music business don't understand the technology they use and just pass on whatever lore they grew up with. So I don't accept anyone's opinion on technology matters unless I know that they are experts in the technology, as apposed to the use of the technology to create music. And even then I don't accept it without confirmation from others of similar experience.

Quote:
It's generally considered bad practice to run phantom through a 1/4 inch (or TT) patchbay, as plugging in out out with the phantom active shorts out the phantom supply - not good......
This has been widely discussed and lots of people who know about such things, as apposed to have just grown up hearing lore, indicate that that as long as you don't just leave it half plugged in, it's fine. The quick short will not damage anything. Maybe that was the case back in the old days, evidently not anymore.

As many of them have pointed out, lots of studios have their console inputs and outputs run through a patch bay, and therefore the phantom power on the console has to go through the patch bay. So clearly it can't be a basic problem in terms of grounding issues. And plenty of folks use TRS patch bays, and I don't hear of them complaining how they are blowing up equipment right and left.
Old 31st May 2009 | Show parent
  #22
Quote:
Originally Posted by Teddy Ray View Post
Yessir.....but he says it is fine.. let him do it.
I never said it was fine. Don't put words in my mouth. I said that lots of people do it all the time and they have no problems with it. I indicated that I do have a problem with it, and that I'm going to have to work around it in my case.
Old 31st May 2009 | Show parent
  #23
Quote:
Originally Posted by John Eppstein View Post
Well, yes, generally you run a DI box into a mic input - unless it's one of those "preamp-DI" things......

I had assumed from the post that were are talking about console preamps here (hence the difficulty of patching), not outboard. It should be noted that the inputs on a console are generally NOT suitable for use as DIs, as the impedance is too low and will load the typical magnetic pickup. A few outboard preamps (Avalon, etc) have proper HiZ inputs, but I don't see any problem patching into those.......
I have a SCA rack, with two pre-amps and a DI board. The DI only brings the signal up to mic level, not line level. So it has to go into a pre-amp. Climbing around the behind the desk every time I want to do that would be silly, since that's the whole point of having a patch bay.

I'm just going to get an outboard phantom power unit, which will just avoid the whole issue and let me patch into the pre-amp inputs without any problems.

I mean, think about it, to harken back to the music technology issue thread. How many years and you still can't reliably patch a freaking pre-amp into a patch bay? The music industry is a technological backwater in so many ways. Any other industry would have taken care of these problems decades ago probably. And we still use those PITA screw based rack mounts instead of simple 'slide it in and lock it down' scheme. Primitive stuff.
Old 31st May 2009 | Show parent
  #24
Oh well, screw it. I decided not to add any more complexity to the system. I'll just climb back there and change the cabling between the mic and DI as required.
Old 31st May 2009 | Show parent
  #25
Lives for gear
 
Teddy Ray's Avatar
 

Quote:
Originally Posted by Dean Roddey View Post
It's got nothing to do with respect. Clearly a lot of people disagree with him, and they aren't idiots. My problem is that he makes a lot of oracular statements that are clearly more his opinion than fact, and then anyone who questions him inevitably gets the "But it's Bob Ohlson" thing.
you still spelled it wrong...OLHSSON(also disrespectful). His opinion is worth its weight in gold to me...because he has the experience to back it up! and by the very merit of his age alone, you should show him respect.
but manners aren't important to everyone...

so let me get this right.. you post seeking advice, most tell you NOT to do it, and you argue with them..I mean..if you have it figured out already, why even ask?
Old 31st May 2009 | Show parent
  #26
Motown legend
 
Bob Olhsson's Avatar
 

I'm certainly not the ultimate expert but I have had endless problems with phantom in patch-bays over the years. It's probably because I'm old school enough to use patch-bays a lot. It's also not a great idea to run mike level signals through patch bays and normals.

Sure, lots of studios do it. That still doesn't make it a very good idea.
Old 31st May 2009 | Show parent
  #27
I didn't argue with anyone. I pointed out that the blanket statements that it won't work or that it's inherently bad are incorrect. It does work for many people and it's not going to blow anything up, as proven by the fact on that ground that people aren't blowing things up all the time.

I was asking for some advice on how I might get mine to work. No one offered any, they just kept indicating it won't work, which is clearly not true. If everyone out there said, no, don't do that, then I wouldn't even be asking the question because I wouldn't even be trying to do it. I only asked because clearly many people do it successfully. So being told it won't work wasn't really information I needed to know. I've already read all the discussions where half of the people say yes and half say no. Clearly half the people in those threads are not hallucinating or idiots.

As to his age, give me a break. I'm 47. I don't expect anyone here who is 20 to take my work for anything because of that, including in my area of expertise, in which my experience is considerable. I have to back up what I say just like everyone else.
Old 31st May 2009 | Show parent
  #28
Quote:
Originally Posted by Bob Olhsson View Post
I'm certainly not the ultimate expert but I have had endless problems with phantom in patch-bays over the years. It's probably because I'm old school enough to use patch-bays a lot. It's also not a great idea to run mike level signals through patch bays and normals.

Sure, lots of studios do it. That still doesn't make it a very good idea.
It's obviously not a good idea for me, this is true. So I'll be, in honor of you, going old school on this one and just walking (well squeezing) behind the desk and flipping cables to deal with it. I'm flabbergasted that this industry is seemingly incapble of dealing with so obvious an issue though. The danger of destroying something is a lot higher, in my opinion, from crawling around behind the desk and whacking something, so I'd have preferred not to.
Old 31st May 2009 | Show parent
  #29
I have an xlr patch bay for this very reason. bigger, bulky, but it works without fail, and no climbing behind the desk.

Quote:
Originally Posted by Dean Roddey View Post
It's obviously not a good idea for me, this is true. So I'll be, in honor of you, going old school on this one and just walking (well squeezing) behind the desk and flipping cables to deal with it. I'm flabbergasted that this industry is seemingly incapble of dealing with so obvious an issue though. The danger of destroying something is a lot higher, in my opinion, from crawling around behind the desk and whacking something, so I'd have preferred not to.
Old 31st May 2009 | Show parent
  #30
There just isn't space for that in my case. I have 8 whole rack spaces. One side is the patch bay, Central Station, and the SCA rack. I need the other side free for some upcoming DIY projects. The LA-2A is off to the side on a separate table because there's no space for it. So rack space is at a premium.
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