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Post by srb on May 27, 2021 12:47:09 GMT -6
I have Switchcraft 9625 patchbays here.
I discovered an issue during a tracking session Monday. I generally put up a condenser mic in the main room that I'll use for musician talkback to the CR. It was convenient to run it to Mic Channel 12.
I didn't get any signal. I was having musician issues more than technical ones, so I moved on.
In checking out the issue yesterday and today, I find that a dynamic mic works fine in that channel, the AKG C414 I tried to use in session did not. It appears that Channel 12 will not pass phantom power.
While holding the AKG in my hand yesterday in trying to test, some bare skin on my leg touched a metal surface (a preamp face?) in the rack where the patchbays also are, and I felt a mild shock.
I've checked all my mic cables and wall connections and everything seems fine there.
The issue appears particular to this channel only.
Am I looking at a single channel grounding issue in the patchbay? Could the ground have changed from the plug/unplug process?
Thanks for any input!
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Post by johneppstein on May 28, 2021 13:40:41 GMT -6
I have Switchcraft 9625 patchbays here. I discovered an issue during a tracking session Monday. I generally put up a condenser mic in the main room that I'll use for musician talkback to the CR. It was convenient to run it to Mic Channel 12. I didn't get any signal. I was having musician issues more than technical ones, so I moved on. In checking out the issue yesterday and today, I find that a dynamic mic works fine in that channel, the AKG C414 I tried to use in session did not. It appears that Channel 12 will not pass phantom power. While holding the AKG in my hand yesterday in trying to test, some bare skin on my leg touched a metal surface (a preamp face?) in the rack where the patchbays also are, and I felt a mild shock. I've checked all my mic cables and wall connections and everything seems fine there. The issue appears particular to this channel only. Am I looking at a single channel grounding issue in the patchbay? Could the ground have changed from the plug/unplug process? Thanks for any input! Certainly sounds like a grounding issue. Thought those "no solder" bays were supposed to be foolproof. |
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Post by srb on May 28, 2021 16:40:25 GMT -6
I have Switchcraft 9625 patchbays here. I discovered an issue during a tracking session Monday. I generally put up a condenser mic in the main room that I'll use for musician talkback to the CR. It was convenient to run it to Mic Channel 12. I didn't get any signal. I was having musician issues more than technical ones, so I moved on. In checking out the issue yesterday and today, I find that a dynamic mic works fine in that channel, the AKG C414 I tried to use in session did not. It appears that Channel 12 will not pass phantom power. While holding the AKG in my hand yesterday in trying to test, some bare skin on my leg touched a metal surface (a preamp face?) in the rack where the patchbays also are, and I felt a mild shock. I've checked all my mic cables and wall connections and everything seems fine there. The issue appears particular to this channel only. Am I looking at a single channel grounding issue in the patchbay? Could the ground have changed from the plug/unplug process? Thanks for any input! Certainly sounds like a grounding issue. Thought those "no solder" bays were supposed to be foolproof. It's really kinda weird. I was certainly surprised by the shock. |
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Post by johneppstein on May 28, 2021 18:57:53 GMT -6
Certainly sounds like a grounding issue. Thought those "no solder" bays were supposed to be foolproof. It's really kinda weird. I was certainly surprised by the shock. I use Switchcraft bays, but I use the long frame ones you have to solder. Never had a problem with 'em. Have not used the newfangled "no solder" ones with switchable normalling. Any time you have a superfluous switch it's a potential problem. |
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Post by jmoose on May 29, 2021 22:50:36 GMT -6
Why do you think it's a ground problem?
Phantom power travels pins 2 & 3... like a 3 prong Edison outlet there should be zero volts at ground.
??
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Post by srb on May 29, 2021 23:52:59 GMT -6
Why do you think it's a ground problem? Phantom power travels pins 2 & 3... like a 3 prong Edison outlet there should be zero volts at ground. ?? I got a mild shock, so that was the first thing that came to mind. |
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Post by johneppstein on May 30, 2021 11:31:44 GMT -6
Why do you think it's a ground problem? Phantom power travels pins 2 & 3... like a 3 prong Edison outlet there should be zero volts at ground. ?? Because I'm aware of similar problems that turned out to be grounding related. For example a loose ground inside a mic itself. Grounding is not always related to either power supplies or AC.
Obviously you're not a tech. Teching is not about what "should be". It's about what IS - and shouldn't.
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Post by jmoose on May 30, 2021 15:21:15 GMT -6
I got a mild shock, so that was the first thing that came to mind. If there's voltage present on the body of the mic it's easy enough to test with a multimeter. Frankly though I suspect there's probably something else going on... FWIW whenever I have a problem with gear on a session I'll take the suspect stuff, all mics cables etc and set 'em to the side so I can try to recreate the problem later. At least half the time I can't recreate it & chalk the experience up to a miscue in the heat of battle. At least half of the other half is usually a single bad cable. Maybe the last 20% is something that actually failed & needs repair. Ideally isolate & test each piece of the circuit, bypass patchbay and plug mics right into the suspect preamp etc. Process of elimination. I would suspect a failed mic or preamp before patchbay, never really heard of ground going bad in a bay. Also if the dynamic mic works as intended then ground should be present? If you lost a pin it'd be "single ended" and would sound like there's a massive high pass filter along with a possible gain drop. So to me, from afar... if the dynamic mic works 100% then that likely rules out a wiring issue and points at something else? |
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Post by johneppstein on May 30, 2021 17:42:07 GMT -6
I got a mild shock, so that was the first thing that came to mind. If there's voltage present on the body of the mic it's easy enough to test with a multimeter. Frankly though I suspect there's probably something else going on... FWIW whenever I have a problem with gear on a session I'll take the suspect stuff, all mics cables etc and set 'em to the side so I can try to recreate the problem later. At least half the time I can't recreate it & chalk the experience up to a miscue in the heat of battle. At least half of the other half is usually a single bad cable. Maybe the last 20% is something that actually failed & needs repair. Ideally isolate & test each piece of the circuit, bypass patchbay and plug mics right into the suspect preamp etc. Process of elimination. I would suspect a failed mic or preamp before patchbay, never really heard of ground going bad in a bay. Also if the dynamic mic works as intended then ground should be present? If you lost a pin it'd be "single ended" and would sound like there's a massive high pass filter along with a possible gain drop. So to me, from afar... if the dynamic mic works 100% then that likely rules out a wiring issue and points at something else? I should point out that I suggested a grounding problem but I DID NOT state that it had to do with the bay, although that possibility has not been eliminated.
There is at least as strong a possibility that it's somewhere else.
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Post by johneppstein on May 30, 2021 17:43:11 GMT -6
I got a mild shock, so that was the first thing that came to mind. If there's voltage present on the body of the mic it's easy enough to test with a multimeter. Frankly though I suspect there's probably something else going on...The problem DOES NOT have to involve voltages present on the mic body or anywhere else. There isa a common problem with certain Gefell mics that involves a sometimes bad connection in the grounding. It DOES NOT involve measurable voltages. It DOES involve a bad ground connection. Similar problems have also been found in other mics from different builders. You want to learn more? There are a couple of threads over at PRW that discuss this.Dig it - it's not a voltage problem - it's a lack of grounding. Zero voltage on both sides, but inadequate ground. |
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Post by srb on May 30, 2021 19:01:28 GMT -6
Thanks for some direction here. I will begin checking some of these other elements as prescribed here.
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Post by Ward on May 31, 2021 13:28:00 GMT -6
Thanks for some direction here. I will begin checking some of these other elements as prescribed here. I can only relate my own experiences here, not someone else's or the theoretical. As johneppstein intimated IME, 9625s are not always great with phantom power! They are fantastic at everything else! So what to do? I have two 96 point TT patch bays in the main patch field dedicated to microphone lines (64 of them) And microphone preamp inputs. There are also 64 of them. None of these are normalled. All have to be patched. Phantom doesn't leak or cross-talk. The end of the second bay has all the feeds for headphone and fold back sends. Never an issue with them. All individual inputs and outputs means nothing can get cross-wired nor can interference occur. Nothing is common grounded...nothing rides the rails for free. It works. |
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Post by srb on May 31, 2021 16:09:26 GMT -6
Thanks for some direction here. I will begin checking some of these other elements as prescribed here. I can only relate my own experiences here, not someone else's or the theoretical. As johneppstein intimated IME, 9625s are not always great with phantom power! They are fantastic at everything else! So what to do? I have two 96 point TT patch bays in the main patch field dedicated to microphone lines (64 of them) And microphone preamp inputs. There are also 64 of them. None of these are normalled. All have to be patched. Phantom doesn't leak or cross-talk. The end of the second bay has all the feeds for headphone and fold back sends. Never an issue with them. All individual inputs and outputs means nothing can get cross-wired nor can interference occur. Nothing is common grounded...nothing rides the rails for free. It works. I just may non-normal my mic lines/pre's in. I wind up patching 90% of those connections anyway. I need to do one last test on the preamp: I have to pull it from the console to test directly. I don't, however, think it's the preamp. It works with the mic (AKG C414) and cables in questions on all the other channels/patches I've tested. No voltage on the mic body that I can find. I will continue to see if I can reproduce the mild shock. So far, I haven't. |
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Post by jmoose on Jun 1, 2021 15:51:00 GMT -6
I just may non-normal my mic lines/pre's in. I wind up patching 90% of those connections anyway. I need to do one last test on the preamp: I have to pull it from the console to test directly. I don't, however, think it's the preamp. It works with the mic (AKG C414) and cables in questions on all the other channels/patches I've tested. No voltage on the mic body that I can find. I will continue to see if I can reproduce the mild shock. So far, I haven't. Ohh. I didn't realize we were talking about normaled connections... Could probably have a long debate over this but generally speaking I'm not a fan of having mic lines on a TT bay and certainly not mixed in with everything else. My personal spot is an open room so its easy enough to direct patch all mics but if I needed a mic level bay? XLR. No hesitation. I did the normalized mic connection thing many years ago, for me it created more grief then anything else and didn't last long. Things can get seriously funky at times because its all too easy for the mic to start feeding two preamps... that messes with phantom and another big one, loading because the mic ends up seeing two preamps. If you got a shock from the mic body there would have to be at least minimal voltage present & fairly repeatable. Are you sure it wasn't static? |
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Post by srb on Jun 1, 2021 23:32:30 GMT -6
I just may non-normal my mic lines/pre's in. I wind up patching 90% of those connections anyway. I need to do one last test on the preamp: I have to pull it from the console to test directly. I don't, however, think it's the preamp. It works with the mic (AKG C414) and cables in questions on all the other channels/patches I've tested. No voltage on the mic body that I can find. I will continue to see if I can reproduce the mild shock. So far, I haven't. Ohh. I didn't realize we were talking about normaled connections... Could probably have a long debate over this but generally speaking I'm not a fan of having mic lines on a TT bay and certainly not mixed in with everything else. My personal spot is an open room so its easy enough to direct patch all mics but if I needed a mic level bay? XLR. No hesitation. I did the normalized mic connection thing many years ago, for me it created more grief then anything else and didn't last long. Things can get seriously funky at times because its all too easy for the mic to start feeding two preamps... that messes with phantom and another big one, loading because the mic ends up seeing two preamps. If you got a shock from the mic body there would have to be at least minimal voltage present & fairly repeatable. Are you sure it wasn't static? My patchbay knowledge continues to be refined through interaction here, and my more recent interactions with mine. I think I may have taken some things for granted (like integrity of signal isolation, grounds, etc.). I appreciate your input here very much. As far as the shock goes, I was (only) holding the mic when my bare leg pressed up against a preamp in a rack. I felt it in the leg, so I'm not very sure at all that it's the mic. It felt akin to what a 9v battery might give. Not static, for sure. I'm going to see if I can recreate that. I don't relish the prospect no matter how mild , as I'm a bit skittish in that respect.
I reserve the right to think I imagined the more recent studio episode...and that something else is going on (early lunacy onset?). 
I did redo the normals today, but haven't seen if that makes any difference in that lone connection not passing phantom. Had some editing and mix work to do that kept me from it.
Again, I appreciate the input I'm getting here on this. |
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Post by johneppstein on Jun 6, 2021 11:45:26 GMT -6
Also if the dynamic mic works as intended then ground should be present? If you lost a pin it'd be "single ended" and would sound like there's a massive high pass filter along with a possible gain drop. So to me, from afar... if the dynamic mic works 100% then that likely rules out a wiring issue and points at something else? No, it could still be a ground problem, expecially (but not limited to) if the problem mic is tube.
Understand, if the problem is ground related it's probably a loose wire or contact somewhere, probably in the mic or PS if there is one.
I have encountered grounding problems in patch bays, but not good ones. And anything containing a switch can develop noise problems. Which is why I don't like switch selectable normalling schemes. Who changes their normalling often enough for it to be a problem, anyway?
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Post by srb on Jun 6, 2021 14:04:11 GMT -6
Also if the dynamic mic works as intended then ground should be present? If you lost a pin it'd be "single ended" and would sound like there's a massive high pass filter along with a possible gain drop. So to me, from afar... if the dynamic mic works 100% then that likely rules out a wiring issue and points at something else? No, it could still be a ground problem, expecially (but not limited to) if the problem mic is tube.
Understand, if the problem is ground related it's probably a loose wire or contact somewhere, probably in the mic or PS if there is one.
I have encountered grounding problems in patch bays, but not good ones. And anything containing a switch can develop noise problems. Which is why I don't like switch selectable normalling schems. Who changes their normalling often enough for it to be a problem, anyway?
The mic (used when this problem presented itself) is an AKG C414. It works in the preamp in question, just not patched through channel 12. Channel 12's cabling tests well from wall plate input to the return in the CR. I haven't made time to suss out any other possibilities at this point. I am going to get behind the rack and tighten/reseat the db25 connector. You make a good point on changing normalling schemes: just doesn't happen much here. |
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ericn
Temp
Balance Engineer
Posts: 14,934 
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Post by ericn on Jun 7, 2021 18:27:18 GMT -6
No, it could still be a ground problem, expecially (but not limited to) if the problem mic is tube.
Understand, if the problem is ground related it's probably a loose wire or contact somewhere, probably in the mic or PS if there is one.
I have encountered grounding problems in patch bays, but not good ones. And anything containing a switch can develop noise problems. Which is why I don't like switch selectable normalling schems. Who changes their normalling often enough for it to be a problem, anyway?
The mic (used when this problem presented itself) is an AKG C414. It works in the preamp in question, just not patched through channel 12. Channel 12's cabling tests well from wall plate input to the return in the CR. I haven't made time to suss out any other possibilities at this point. I am going to get behind the rack and tighten/reseat the db25 connector. You make a good point on changing normalling schemes: just doesn't happen much here. This is where those stupid solderless XLR’s comes in handy. While using a VOM should show if the cable is the problem, physically duplicating the entire routing without the bay is always the best way to track the problem. Reading the thread normal status won’t effect much here. Go take a look at any switching jack, the switching and normal long matrix won’t effect the ground path. |
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