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"Hot plugging" XLR with phantom power on
Old 5th April 2008
  #1
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"Hot plugging" XLR with phantom power on

Is is dangerous for a mic to plug in its XLR cable while the phantom power is switched on? Does this 48 volt jolt have any negative effect?
Large and small condensers, not ribbons.
Old 5th April 2008
  #2
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Harley-OIART's Avatar
 

In my experience, no it does not. However I am not an electronics engineer, only a live + studio sound man. The only thing I worry about with phantom is hot patching when output is being fed to the poweramps and in-turn speakers -> thats a nasty pop at times. [Especially with an evil deadly intermittent cable which causes 5 pops in a second because the phantom keeps cutting in and out every time the caterer steps on the xlr ]

Regardless, I am interested to hear replies

Old 5th April 2008
  #3
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You can put a nasty voltage spike into the mic preamp front end by hot plugging a mic with phantom power enabled. Visualize a 48V step in a circuit designed to amplify millivolts. This is known to preamp designers and typically protected against with input clamp circuitry.

You will usually just get a loud click/thump, but it is good practice to plug/unplug mics with phantom power off.

JR
Old 5th April 2008
  #4
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Minion's Avatar
 

I guess it would depend on the pre-amp....Most preamps should have Hot plugging protection but I have come across a few that didn"t have any protection at all....Most Protection schemes I have seen just use a Pair of Diodes connected to the input leads and then each diode is then connected to +v and -v ,But I have also seen them connected to ground....

Cheers
Old 5th April 2008
  #5
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Most engineers turn the CTR volume down before they switch mics..
This is why I have a ramp up voltage on the JM-130 pre, reduces this pop quite a bit..
Old 6th April 2008
  #6
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With regard to hurting the actual microphone
I've been thinking about this thread all day since I read it last night. When you turn on a phantom power switch contact is closed (is made) and 48 volts go down two conductors of the cord and hit the mike's (or mic's)circuit and capsule. When you plug onto a cord connected to an allready turned on preamp, console, or phantom power supply, a contact is made and 48 volts go through two pins of the mike's xlr and hits the mike's circuit and capsule. Where's the difference (rhetorical)?
The only reason not to do it would be the the possible damage to the preamp or thump produced and protecting your speakers. Some may reason that perhaps plugging in the mike and then turning the pre on would somehow place a softer blow to the mike due to the power supplies' rise time because that will be different in every model of power supply and is an unknown quantity, and even there you may be exposing the mike to some even harsher transients that aren't intended to be part of audio chain. IMHO
Old 6th April 2008
  #7
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I accidentally unplugged a mic from a Safesound P1 with the phantom power on and it hosed the pre. Had to send it in for repairs. That's a mistake I'll hopefully never make again.

Don't know how common that is, but it does happen.
Old 6th April 2008
  #8
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Disengaging phantom power is one of those things you must to get in the habit of doing, or else sooner or later, you're gonna pay.


-SD
Old 6th April 2008
  #9
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JohnRoberts's Avatar
 

Quote:
Originally Posted by larrykane View Post
With regard to hurting the actual microphone
I've been thinking about this thread all day since I read it last night. When you turn on a phantom power switch contact is closed (is made) and 48 volts go down two conductors of the cord and hit the mike's (or mic's)circuit and capsule. When you plug onto a cord connected to an allready turned on preamp, console, or phantom power supply, a contact is made and 48 volts go through two pins of the mike's xlr and hits the mike's circuit and capsule. Where's the difference (rhetorical)?
The only reason not to do it would be the the possible damage to the preamp or thump produced and protecting your speakers. Some may reason that perhaps plugging in the mike and then turning the pre on would somehow place a softer blow to the mike due to the power supplies' rise time because that will be different in every model of power supply and is an unknown quantity, and even there you may be exposing the mike to some even harsher transients that aren't intended to be part of audio chain. IMHO
The difference between hot plugging and switching the phantom power supply on/off, is that the preamp input capacitors can be sitting there charged up to phantom voltage and momentarily shorted to ground or a low impedance.

This suggests that input clamp circuitry may need to handle amps of discharge current. I have had no problem using more modest clamp diodes, but even small signal diodes can handle momentay peaks of 1A.

When powering up the phantom supply after mic is plugged in, the phantom voltage is supplied through 6.8k resistors which limits current to mA levels.

JR
Old 19th April 2008
  #10
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Newbie here, made a mistake (once) and unplugged a condenser connected directly to a portable recorder. Everything seems fine (phew!) after testing for damage, but how can I be sure that indeed no harm was inflicted on the mics or the Korg? Is this something I would have noticed? Or can the damage be subtle and hard to hear at first?
Old 19th April 2008
  #11
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Okay, lots of "near misses".

Has anyone actually damaged a piece of gear by 'hot plugging'?

First hand accounts only, please.
Old 19th April 2008
  #12
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Minion's Avatar
 

VocalVoodoo in post 8 said he has....??
Old 19th April 2008
  #13
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Quote:
Originally Posted by tenchijin2 View Post
Okay, lots of "near misses".

Has anyone actually damaged a piece of gear by 'hot plugging'?

First hand accounts only, please.
This is mostly a cosmetic (noise) issue with properly designed gear, but there's always new gear coming along where new designers may not know better. I've been aware of need to to protect mic pre front ends for decades.

I recall when wireless mics first came out, many didn't properly protect output stages where they plugged into mic inputs and they lost a bunch of early production models to phantom voltage backing up into the output, until they beefed up designs. Not exactly a hot plugging issue but phantom power and design related.

JR
Old 19th April 2008
  #14
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Forgive my newbie-ness: How do I know whether I caused damage? Is it something that I would hear immediately? Or could it be a subtler damage that requires testing/measurements to detect?
Old 20th April 2008
  #15
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If it was well designed you couldn't break it. It's probably fine. If it sounds good it is good.


JR
Old 20th April 2008
  #16
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Quote:
Originally Posted by sonicdefault View Post
Disengaging phantom power is one of those things you must to get in the habit of doing, or else sooner or later, you're gonna pay.


-SD
how do you do that if a console has a global phantom supply that is not easy to turn off?

if your all your gear is reasonably designed (anything modern should be) and there are no mis wired cables the only problem your going to have is a pop of noise so just make sure you mute any channel you are turning plugging or turning phantom on or off for, or mute your master output. it is possible to kill a line output by plugging it into a mic input with phantom, but thats another story.
Old 20th April 2008
  #17
DNR
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hot plugging can kill a ribbon. otherwise, loud spikes out the monitors suck but i haven't killed a pre or non-ribbon mic in my moments of fogetfulness...
Old 20th April 2008
  #18
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Quote:
Originally Posted by JohnRoberts View Post
The difference between hot plugging and switching the phantom power supply on/off, is that the preamp input capacitors can be sitting there charged up to phantom voltage and momentarily shorted to ground or a low impedance.

This suggests that input clamp circuitry may need to handle amps of discharge current. I have had no problem using more modest clamp diodes, but even small signal diodes can handle momentay peaks of 1A.

When powering up the phantom supply after mic is plugged in, the phantom voltage is supplied through 6.8k resistors which limits current to mA levels.

JR
You seem well versed-but what would be the electrical route for the short with an XLR? TRS certainly, as the tip touches the shield during insertion but where with xlr? not quarreling- genuinely looking to learn
Old 20th April 2008
  #19
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That is a good question.. AFAIK most common shorts are associated with plugging into or out of patch bays when tip contact shorts two circuits together.

XLRs look like they should be harmless.

JR
Old 23rd April 2008
  #20
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I want to clarify about the difference between turning off phantom power and hot-plugging. I agree with everyone who said that it often doesn't result in damaged equipment. I also agree with those who said you should turn off phantom when plugging or unplugging microphones, always!
The key issue is that if phantom power is on, and either voltage-carrying pin connects a split-second before the other, you can potentially damage the ICA circuitry inside a condenser microphone. Turning off phantom power is a good habit to get into.
Old 24th April 2008
  #21
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sonicdefault's Avatar
Quote:
Originally Posted by aussie_techie View Post
how do you do that if a console has a global phantom supply that is not easy to turn off?

if your all your gear is reasonably designed (anything modern should be) and there are no mis wired cables the only problem your going to have is a pop of noise so just make sure you mute any channel you are turning plugging or turning phantom on or off for, or mute your master output. it is possible to kill a line output by plugging it into a mic input with phantom, but thats another story.
In situations where being this careful isn't practical, well... I think we've all been there. I've hot swapped quite a few mics in my day. I've also seen a few mics mysteriously stop working. So for me, the most reasonable solution is to get in the habit of applying phantom last whenever possible.


-SD
Old 24th April 2008
  #22
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So I'm selling a little inline switch unit to remedy this problem.. I figure about 35 bucks. It has a switchcraft female in a 2x2x4 box with a dpst switch that cuts both signal legs and a hard wired 10" switchcraft xlr male for using at the floor box or console end so you won't have to tie up any extra mike cords. PM if interested. Named phantom-cutter. Money back guarantee to Continental US
Old 24th April 2008
  #23
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Quote:
Originally Posted by larrykane View Post
So I'm selling a little inline switch unit to remedy this problem.. I figure about 35 bucks. It has a switchcraft female in a 2x2x4 box with a dpst switch that cuts both signal legs and a hard wired 10" switchcraft xlr male for using at the floor box or console end so you won't have to tie up any extra mike cords. PM if interested. Named phantom-cutter. Money back guarantee to Continental US
This is interesting. Does it have the ability to softly ramp the power back up when you re-engage the switch?


-SD
Old 24th April 2008
  #24
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Quote:
Originally Posted by sonicdefault View Post
This is interesting. Does it have the ability to softly ramp the power back up when you re-engage the switch?


-SD
Not yet - But by using a stereo pot instead of a switch would do that, and in full on it would be out of circuit. That work for you?
Old 24th April 2008
  #25
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Quote:
Originally Posted by DNR View Post
hot plugging can kill a ribbon. otherwise, loud spikes out the monitors suck but i haven't killed a pre or non-ribbon mic in my moments of fogetfulness...
I work at a studio with an old Neve V1 that always has phantom on. been using ribbons for quite some time
Old 24th April 2008
  #26
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"Originally Posted by DNR
hot plugging can kill a ribbon. otherwise, loud spikes out the monitors suck but i haven't killed a pre or non-ribbon mic in my moments of fogetfulness...

I work at a studio with an old Neve V1 that always has phantom on. been using ribbons for quite some time"

I think the real danger is when dealing with a transformerless non-condenser microphone; phantom power mistakenly applied to a dynamic mic without one will definitely harm the diaphragm. I'm not sure that there are many modern dynamics without a tranny (even ribbons), I seem to remember the AKG D12e not having one...probably many other vintage ribbons and moving coils, too. Be careful with global phantom!
Old 24th April 2008
  #27
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Quote:
Originally Posted by Idiophonic View Post
I think the real danger is when dealing with a transformerless non-condenser microphone; phantom power mistakenly applied to a dynamic mic without one will definitely harm the diaphragm. I'm not sure that there are many modern dynamics without a tranny (even ribbons), I seem to remember the AKG D12e not having one...probably many other vintage ribbons and moving coils, too. Be careful with global phantom!
there are heaps of transformer-less dynamics, ive have never had any problems with any of them due to phantom or heard of any one else having any problems.
Old 25th April 2008
  #28
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You are correct, this made me go back and educate myself! There is still a risk, though.

"Phantom power has the advantage that a dynamic or ribbon mic may
be plugged in to a phantom powered microphone input and operate
without damage, and a phantom powered mic can be plugged in to
the same input and receive power. The only hazard is that in case
of a shorted microphone cable, or certain old microphones having
a grounded center tap output, current can flow through the
microphone, damaging it.
It's a good idea anyway to check cables
regularly to see that there are no shorts between any of the
pins, and the few ribbon or dynamic microphones with any circuit
connection to ground can be identified and not used with phantom
power."

This article is from the Audio Professional FAQ
Old 25th April 2008
  #29
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nosebleedaudio's Avatar
 

Quote:
Originally Posted by Idiophonic View Post
You are correct, this made me go back and educate myself! There is still a risk, though.

"Phantom power has the advantage that a dynamic or ribbon mic may
be plugged in to a phantom powered microphone input and operate
without damage, and a phantom powered mic can be plugged in to
the same input and receive power. The only hazard is that in case
of a shorted microphone cable, or certain old microphones having
a grounded center tap output, current can flow through the
microphone, damaging it.
It's a good idea anyway to check cables
regularly to see that there are no shorts between any of the
pins, and the few ribbon or dynamic microphones with any circuit
connection to ground can be identified and not used with phantom
power."

This article is from the Audio Professional FAQ
If this happens you WILL know it, will have hum and or buzz.
Have seen this a few times...
Old 25th April 2008
  #30
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nosebleedaudio's Avatar
 

Quote:
Originally Posted by sonicdefault View Post
This is interesting. Does it have the ability to softly ramp the power back up when you re-engage the switch?


-SD
The soft ramping needs to be in the mic pre, I have one in the JM-130 pre, pretty big difference...I could post a comparison
It should be before the phantom resistors to work best.
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