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Post by johneppstein on Jan 1, 2018 16:32:50 GMT -6
Ah, I KNEW George Lucas didn't come up with it by himself!
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Post by johneppstein on Jan 1, 2018 16:41:54 GMT -6
Guess I'll have to just get two more dedicated Mic pres You won't have any problems if you just remember to always patch before turning on phantom, and turn off phantom before un-patching. People have been doing this for 30 years+. I don't really understand what the problem is. Well, wait tiil you grow up and your memory starts getting.... what was I talking about?
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Post by johneppstein on Jan 1, 2018 16:46:11 GMT -6
So have we all agreed that hot plugging is bad? Nope. I guess all those large console manufacturers and some of the largest and most well-known studios in the world are all doing it wrong by allowing hot plugging in their patch bays. Most phantom supplies have limiting resistors that can take the surge from hot plugging. However, that's not the same as accidentally half-inserting your plug and grounding out the phantom supply though. You'll certainly have a burnt resistor from that. Everybody makes misteaks. Everybody.
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Post by johneppstein on Jan 1, 2018 17:08:34 GMT -6
I've been following the Flock thread recently, and phantom power in a patchbay came up again. Anyway, that led to me randomly circling back to this thread. Something that never got mentioned in this thread is 500 series preamps (or other preamps without a dedicated line input) which have a switch allowing for running line input signals into the preamp. Preamps with mic/line switches (and only ONE input point) to accommodate line inputs for adding color are common these days. It would take some pretty complicated wiring to NOT have those kind of preamps wired up in a TT patchbay. For those of you advocating for an XLR bay for mic inputs, how are also accommodating for line input into those preamps which do not have a second input for line level? I have all of my preamps (inputs and outputs) wired to TT patchbays to allow for this, but I also exclusively use external phantom power supplies to specifically avoid EVER using the phantom power on my preamps and the potential issues that could arise by doing so through a TT patchbay. I'm just curious how some of you XLR mic bay guys are accommodating line level through your preamps? That's a very good question. In my case the answer is that I don't, because line level signals generally come in to the line ins on my console, not into the outboard mic pre's. If I want line inputs into an outboard pre for that I can use my A-Designs KGB-2 instrument preamp, but that seldom comes up. Don't most outboard preamps have a seperate 1/4" line in, anyway? My A-Designs Ventura does, but I use that as the preamp in my (acoustic) guitar (stage) rig. If I routinely used line ins on outboard pre's I imagine that I'd probably get out by drill and add 1/4" line ins to the XLR panel. I've also got 4 Countryman Type 85s that see a fair amount of use.
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Post by johneppstein on Jan 1, 2018 17:19:56 GMT -6
Quint - excellent solution. IMO, the best idea I've seen. I may employ that. What external 48v supplies do you use? Well, I'm obviously not Quint, but I'd like to point out that an external phantom supply (of one to many channels) would be an excellent and very simple first DIY project.
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Post by johneppstein on Jan 1, 2018 17:22:35 GMT -6
They where out of production when I bought them. You can still find them out there on eBay. I'm sure other companies still make a similar product. I imagine that, if you had to, you could find someone to build you an external supply. They're pretty simple in design. Yes, there are a few floating around. Pretty cheap construction and kind of dubious. Mostly single channel or dual channel. I wouldn't really be interested in kludging a bunch of stomp box sized 48v solutions together. An 8-12 channel single rack space unit would be ideal. Will keep my eyes open for one..... You could even integrate it with your XLR panel.
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ericn
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Post by ericn on Jan 1, 2018 17:51:57 GMT -6
I always thought somebody should come up with an install product that provided the phantom at the wall plate but anytime I brought it up manufacturers would dismiss the whole concept!
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Post by EmRR on Jan 1, 2018 18:31:44 GMT -6
If it's transformer out feeding your live phantom pre, it's already isolated. If it's SS, it's a novice manufacturer who hasn't put a clamping diode bridge on the output for protection. Think about EVERY wireless rig that gets patched to a preamp input: it's not a mic, it's a receiver amp outputting mic level. They must have protection or they'd be blown immediately. Cheap gear....no telling. Lots of it tells you NOT to patch to phantom powered inputs, which tells you where they saved a nickel. My preamps here are protected against phantom spikes and shorts. I use a cross wired pair of zener diodes. Those are 1N752A's at 5.6 volts. A pair cross wired in series from each input to ground PAST the blocking caps will prevent any damaging spikes from exceeding 11 volts. The 7xx series zener diodes have lower stray capacitance than the 4xxx series and provide the lowest distortion specs. Another common technique are power rectifier diodes run from the inputs to the power rails. That also works but some front ends will still get some damage if hit at the power rails. I've yet to get a damaged front end in any non-transformer input mic pre design with the clamp zener diodes. It's insurance here. I'm sure that works for preventing preamps from shorting to ground during patching mics. But I was asking about running/patching line level signal into preamps.
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Post by jeremygillespie on Jan 2, 2018 7:57:46 GMT -6
Just checked my Vp-28's and Hairball Lola's. Both pass 48v in Line Mode.
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Post by svart on Jan 2, 2018 8:49:34 GMT -6
Almost all consumer gear has AC coupling on I/O. It's there to protect against DC offsets on the I/O.. They should generally make those caps high enough voltage to resist phantom.. But some might not since they don't expect phantom or sustained high voltages on line I/O..
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Post by Quint on Jan 2, 2018 13:34:28 GMT -6
I didn't mean they were stomp boxes. I meant that they were about stomp box sized. There are several units out there. But none that really appealed to me. Yes, the one you linked looked cool, but again, discontinued and none on ebay that I saw. Also, for me, 4 is not enough. I don't EVER want to have to crawl behind a rack to rematch cables. And I want the i/o safely up on the bays. I'm going to talk with BradM about this...... Hopefully I can convince him there's a market like the two of us out there..... Maybe Brad will make one. A rack mount unit would be cool. The way I do it now is to just lay the phantom boxes on the floor in the tracking area next to the XLR panel where all of the mic lines come in and just do my "patching in" of phantom there. I even made XLR cables out of red Mogami (as opposed to black Mogami for the rest) so I could easily tell which mic lines have phantom on them.
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Post by c0rtland on Jan 2, 2018 14:40:50 GMT -6
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Post by EmRR on Jan 2, 2018 15:11:59 GMT -6
I don't know of any that are transformer iso. Cap iso, transformer iso, either one the thing with V series is about the transient spike at turn-on breaking down the winding insulation until the windings short, IIRC. The important thing is series resistance and local capacitance sized for a slow ramp up/down. I don't know the commonly accepted values for safe V series use. Someone here must.
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ericn
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Post by ericn on Jan 2, 2018 21:34:40 GMT -6
There was this guy many thought he was nuts who used the little Crown boxes only. He told me " why not just treat the FET mics just like the tube mics and have the PSU by the mic"?
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Post by Quint on Jan 3, 2018 1:12:16 GMT -6
There was this guy many thought he was nuts who used the little Crown boxes only. He told me " why not just treat the FET mics just like the tube mics and have the PSU by the mic"? EXACTLY how I do it.
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Post by stormymondays on Apr 20, 2021 7:30:10 GMT -6
Guess who just hot plugged through phantom power and fried a Chroma preamp? I was setting up a new lunchbox and making sure I wouldn’t be sending phantom power to my interface’s outputs, testing with a multimeter along the way. I was very careful with the interface. It turns out at the very last step, when all was measured and correct, I plugged in/out my TRS with phantom power engaged. I’m waiting on Brad’s (remote) diagnose of the problem. I suppose I didn’t fry the lunchbox itself. Oh well.
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Post by srb on Apr 20, 2021 10:04:29 GMT -6
I have a sinking suspicion I fried an input transformer and a germanium amp in a Chandler unit (and routed to my patchbay) by having phantom engaged and their being a short in my mic line cable...which is in the wall. I found the break in the line. Had barely just enough slack in it to pull, cut and repair it. With shipping, parts, and labor about a $260 repair. I am now super-phantom conscious. 😕
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Post by mhbunch on Apr 21, 2021 21:38:18 GMT -6
I have a sinking suspicion I fried an input transformer and a germanium amp in a Chandler unit (and routed to my patchbay) by having phantom engaged and their being a short in my mic line cable...which is in the wall. I found the break in the line. Had barely just enough slack in it to pull, cut and repair it. With shipping, parts, and labor about a $260 repair. I am now super-phantom conscious. 😕 I wouldn’t think phantom would fry a transformer?
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Post by EmRR on Apr 22, 2021 8:02:59 GMT -6
I have a sinking suspicion I fried an input transformer and a germanium amp in a Chandler unit (and routed to my patchbay) by having phantom engaged and their being a short in my mic line cable...which is in the wall. I found the break in the line. Had barely just enough slack in it to pull, cut and repair it. With shipping, parts, and labor about a $260 repair. I am now super-phantom conscious. 😕 I wouldn’t think phantom would fry a transformer? Read the AES paper if you haven't. There's a state in which a momentary couple of amps of current can discharge in one direction. That's a bit like an arc welder. Given that old V series preamp don't like phantom AT ALL unless slow charge/discharge, a patchbay short is many orders more 'potential' danger.
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Post by srb on Apr 22, 2021 9:18:32 GMT -6
I wouldn’t think phantom would fry a transformer? Read the AES paper if you haven't. There's a state in which a monetary couple of amps of current can discharge in one direction. That's a bit like an arc welder. Given that old V series preamp don't like phantom AT ALL unless slow charge/discharge, a patchbay short is many orders more 'potential' danger. I appreciate your weighing in more on this, Doug. The situation is a bit more complicated than my original reply here might indicate. I think that's exactly what happened, and ironically, it could well have taken place while I was on a lengthy troubleshooting call with Adam Fiori of Chandler. I have two of those germ pre's, and there was patching back and forth...trying different mic lines, et cetera. There may have been some other factors at work I'm unaware of, but it's a guaranteed current/voltage issue of some type. As I've thought about it more, I think the cable ground was the fault. I know the cable casing must have been damaged upon installation, taped and crammed surreptitiously into the wall plate cavity. That bad ground (probably momentary), given the nature of the cable damage, is the proximate cause. The only other thing I could think of (Chandler, too) was something amiss in the PSU. That was not the case, as it went in for assessment along with the pre. It's this thread that made it all dawn on me. There are only so many things that can go wrong in this situation... I've read some excerpts from that AES paper. I need to do the whole thing.
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Deleted
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Post by Deleted on Sept 6, 2021 23:26:07 GMT -6
I've been following the Flock thread recently, and phantom power in a patchbay came up again. Anyway, that led to me randomly circling back to this thread. Something that never got mentioned in this thread is 500 series preamps (or other preamps without a dedicated line input) which have a switch allowing for running line input signals into the preamp. Preamps with mic/line switches (and only ONE input point) to accommodate line inputs for adding color are common these days. It would take some pretty complicated wiring to NOT have those kind of preamps wired up in a TT patchbay. For those of you advocating for an XLR bay for mic inputs, how are also accommodating for line input into those preamps which do not have a second input for line level? I have all of my preamps (inputs and outputs) wired to TT patchbays to allow for this, but I also exclusively use external phantom power supplies to specifically avoid EVER using the phantom power on my preamps and the potential issues that could arise by doing so through a TT patchbay. I'm just curious how some of you XLR mic bay guys are accommodating line level through your preamps? You could make tie lines that bridge the XLR mic pre input panel and your TT patchbay, using open slots. You still need to keep 48V turned OFF, but you get the separation of church and state and can still plug line inputs into preamps. Upside: It's tidy, and you have two extra connectors to patch in in order to get it connected, giving you more time to ensure you're not making a mistake. Downside: it's an extra two connectors and length of cable. Or, cut out the middleman with TT-to-M-XLR cables. In the case of a 500 rack, you would want that in the XLR patch panel, too, or at least as many channels as you would want dedicated to mic pres, the rest could be in the TT. Kind of messy, but it would work. _____________ While the pedantic view on the Phantom-over-XLR-vs-TT thing is obviously correct, and is to be considered "best practice", the reality is that if it were a genuinely widespread problem, you'd hear a lot more about it. For my own design, I'm still on the fence, but ultimately it adds cost and complexity not to mention takes up more space to do the XLR thing and I might be OK to risk the tiny probability of cooking some piece of hardware as a worthwhile trade off for a simpler setup, with fewer lengths of cable and connectors. It's only ever gonna be on me if that happens and maybe I can live with that.
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Post by Ward on Sept 7, 2021 8:20:04 GMT -6
A slight 'additional info' reply to this thread:
If you have phantom power coming out of preamps or supplies hooked up to your bays, turn off the phantom power when not in use. I had a massive trouble-shooting issue yesterday not able to get a KM84 powered up from my AS1292 500 series preamp yesterday. I eventually found the issue was coming from phantom power coming out of another preamp that was connected to the preamp input bay. Thankfully, my client was patient.
All my preamps are good quality high-end units. I don't recall when this ever happened before. But obviously, it can happen even though it's theoretically impossible. Weird.
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Post by Deleted on Sept 7, 2021 9:39:12 GMT -6
A slight 'additional info' reply to this thread: If you have phantom power coming out of preamps or supplies hooked up to your bays, turn off the phantom power when not in use. I had a massive trouble-shooting issue yesterday not able to get a KM84 powered up from my AS1292 500 series preamp yesterday. I eventually found the issue was coming from phantom power coming out of another preamp that was connected to the preamp input bay. Thankfully, my client was patient. All my preamps are good quality high-end units. I don't recall when this ever happened before. But obviously, it can happen even though it's theoretically impossible. Weird. You mean phantom was coming out of another preamp whose output was connected to another patch point, but it was still affecting the line the 84 was connected to? Some sort of common grounding or...?
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Post by recordingengineer on Sept 7, 2021 12:01:52 GMT -6
Yes, I’m confused exactly what the symptoms were, but yes, I might expect a common ground issue as well… Obviously, tie line and mic preamp input grounds should all be isolated.
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Post by Quint on Sept 7, 2021 13:41:06 GMT -6
I've been following the Flock thread recently, and phantom power in a patchbay came up again. Anyway, that led to me randomly circling back to this thread. Something that never got mentioned in this thread is 500 series preamps (or other preamps without a dedicated line input) which have a switch allowing for running line input signals into the preamp. Preamps with mic/line switches (and only ONE input point) to accommodate line inputs for adding color are common these days. It would take some pretty complicated wiring to NOT have those kind of preamps wired up in a TT patchbay. For those of you advocating for an XLR bay for mic inputs, how are also accommodating for line input into those preamps which do not have a second input for line level? I have all of my preamps (inputs and outputs) wired to TT patchbays to allow for this, but I also exclusively use external phantom power supplies to specifically avoid EVER using the phantom power on my preamps and the potential issues that could arise by doing so through a TT patchbay. I'm just curious how some of you XLR mic bay guys are accommodating line level through your preamps? You could make tie lines that bridge the XLR mic pre input panel and your TT patchbay, using open slots. You still need to keep 48V turned OFF, but you get the separation of church and state and can still plug line inputs into preamps. Upside: It's tidy, and you have two extra connectors to patch in in order to get it connected, giving you more time to ensure you're not making a mistake. Downside: it's an extra two connectors and length of cable. Or, cut out the middleman with TT-to-M-XLR cables. In the case of a 500 rack, you would want that in the XLR patch panel, too, or at least as many channels as you would want dedicated to mic pres, the rest could be in the TT. Kind of messy, but it would work. _____________ While the pedantic view on the Phantom-over-XLR-vs-TT thing is obviously correct, and is to be considered "best practice", the reality is that if it were a genuinely widespread problem, you'd hear a lot more about it. For my own design, I'm still on the fence, but ultimately it adds cost and complexity not to mention takes up more space to do the XLR thing and I might be OK to risk the tiny probability of cooking some piece of hardware as a worthwhile trade off for a simpler setup, with fewer lengths of cable and connectors. It's only ever gonna be on me if that happens and maybe I can live with that. I was just curious how others might be doing it. If an alternative solution involves a bunch of additional connections, I don't love that, but then all of these solutions are some kind of compromise. For my end of things, I'd still rather just not ever have phantom in my bay and use external phantom supplies near the mics to avoid all of these problems being discussed.
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