Disengage phantom before unplugging - a myth?

dpiper · Post by **dpiper** » Wed Oct 18, 2006 3:48 pm

I am confused about phantom power.

Here at audio school, people are continuosly asking "is the phantom off?" before unplugging mics or switching cables. But at the studio where I intern, I am told that phantom is "always on" (thier consoles are a Neve 8608, and a Trident 80b). They seem to connect and unplug condensers, as well as old RCA ribbon mics, without thinking twice about it. I've also read that phantom was simply left on at Abbey Road Studios.

I understand that electronics are more prone to break at a "change of state" (ie, powering on or off). Does turning phantom on/off at the pre-amp make for a more gradual or safer "change of state" than the sudden shock of unplugging a cable?

So, is turning off phantom before unplugging a mic:

1. a good practice that might protect your mics better long term, but does not make a huge difference on an individual basis.

2. really important if you don't want to break things, or

3. an urban myth?

Scodiddly · Post by **Scodiddly** » Wed Oct 18, 2006 3:59 pm

The best discussion I ever found on this was over at the Prosoundweb forums, in Klaus Heyne's mic forum.

1. It's good practice to turn off phantom, because you might get a huge "pop!" in the speakers and blow something out otherwise. Better practice is to always mute channels before changing anything.

2. If there's a transformer involved, either in the mic or the mic pre (or both), the DC jolt can magnetize the transformer slightly and therefore reduce headroom and linearity. If it's a transformerless mic into an electronically-balanced mic pre, no problem.

farview · Post by **farview** » Wed Oct 18, 2006 4:14 pm

I've had my phantom power on since 1997. No problems yet.

bniesz · Post by **bniesz** » Wed Oct 18, 2006 5:26 pm

phantom + ribbon mics? really?
phantom + powered tube mic is a problem, no doubt, right? RIGHT?

farview · Post by **farview** » Wed Oct 18, 2006 8:08 pm

bniesz wrote:phantom + ribbon mics? really?
phantom + powered tube mic is a problem, no doubt, right? RIGHT?

Only very specific ribbon mics will be hurt. (these tend to be old and expensive)
The phantom power won't do anthing to the power supply for the tube mic.

Professor · Post by **Professor** » Wed Oct 18, 2006 8:42 pm

It's not entirely a myth.
It really will hurt some ribbon mics (there's another post from someone who killed an Oktava ML-52).
It will also send nasty thumps & cracks through the system.
And I would hesitate before plugging into an output from a tube power supply, or an active DI on the back of somebody's bass amp, etc.

But hot-plugging into 48v really shouldn't be that different from turning on the 48v with a little switch, because it's not like there are 'soft start' switches in any preamps.

Really it comes down to what is "good practice" and I am a firm believer in the idea that any regular routine you can adopt that will keep you more aware of what the hell you're doing in the studio is really bound to make you a better engineer. That simple act of asking whether the phantom power is on before plugging or unplugging means that you're paying attention to what you're doing, to the kind of mics you have up, and to how things are connected.
It's kinda like using your turn signal. I've forced myself to make it so much of a habit over the years that I occasionally catch myself flipping on the turn signal while rounding a sharp enough turn in a single-lane road, or on empty streches of dirt roads. It's just good practice, and maybe it's saved me from a few tickets over the years, and maybe even a few accidents. I guess I'll never know.

Of course, if you know you're in a studio that has phantom on at all times, you may need to be careful and do things like drop an isolation transformer on the cable dangling out of the back of an old RCA or Oktava ribbon before hot-plugging. $50 for a Sescom ISO-2 is cheaper than $200 for a re-ribbon job.

-Jeremy

tommy · Post by **tommy** » Thu Oct 19, 2006 12:20 am

If you have an old console without the option to turn phantom off then you should always route your signal first (on the patch bay) THEN plug your ribbon mic into the snake. If you do it the other way around (plugging in ribbon mic in first then start patching), you run the risk of zapping your ribbon mic due to the phantom power crossing paths with the wrong wire.

Mark Alan Miller · Post by **Mark Alan Miller** » Thu Oct 19, 2006 5:12 am

tommy wrote:If you have an old console without the option to turn phantom off then you should always route your signal first (on the patch bay) THEN plug your ribbon mic into the snake. If you do it the other way around (plugging in ribbon mic in first then start patching), you run the risk of zapping your ribbon mic due to the phantom power crossing paths with the wrong wire.

Fortunately I can turn phantom off om my consle, beacaue that very action (plugging TRS "hot" on the bay) fries cards in it. Found out the hsrd way...
Something to keep in mind, too.

AudioHog · Post by **AudioHog** » Thu Oct 19, 2006 5:48 am

I was always told to turn off due to TRS patching. Therefor I always have it off til I need it. Unrelated but what would happen if say I'm routing through my ProChannel and supplying 48V there and accidentally turn on phantom power on my project mix on the input channel?

farview · Post by **farview** » Thu Oct 19, 2006 8:51 am

I mainly leave mine on just because I can't easily get to the switch. Once I put the board into the console housing, I have to put the monitors and the screens on the floor, open the top of the housing, flip the switch, put everything back. I have enough channels on the board so I really don't need the patchbay for mic connections.

JASIII · Post by **JASIII** » Thu Oct 19, 2006 12:09 pm

Professor wrote:
Really it comes down to what is "good practice" and I am a firm believer in the idea that any regular routine you can adopt that will keep you more aware of what the hell you're doing in the studio is really bound to make you a better engineer. That simple act of asking whether the phantom power is on before plugging or unplugging means that you're paying attention to what you're doing, to the kind of mics you have up, and to how things are connected.
It's kinda like using your turn signal. I've forced myself to make it so much of a habit over the years that I occasionally catch myself flipping on the turn signal while rounding a sharp enough turn in a single-lane road, or on empty streches of dirt roads. It's just good practice, and maybe it's saved me from a few tickets over the years, and maybe even a few accidents. I guess I'll never know.

That's great advice. I try to take a similar approach.

dpiper · Post by **dpiper** » Thu Oct 19, 2006 12:16 pm

Wow, a variety of good advice from lots of folks... thanks.

bniesz · Post by **bniesz** » Thu Oct 19, 2006 12:36 pm

farview wrote:
bniesz wrote:phantom + ribbon mics? really?
phantom + powered tube mic is a problem, no doubt, right? RIGHT?
Only very specific ribbon mics will be hurt. (these tend to be old and expensive)
The phantom power won't do anthing to the power supply for the tube mic.

you're telling me that if i popped on phantom to a U67 I'd be ok?!

JASIII · Post by **JASIII** » Thu Oct 19, 2006 2:17 pm

I've already run phantom to my MXL V69, which has a power supply and is tube, and nothing bad happened. It worked with and without phantom.

RodC · Post by **RodC** » Thu Oct 19, 2006 3:12 pm

One thing I believe, where the connection is being broken/made there will be an arch. Yes it is low current but you can see it if you try. The switch was made to handle making/breaking the connection. The nice clean gold xlr connector on that shiny mic isnt. This may lead to a bad connection if you pratice it a lot.

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Disengage phantom before unplugging - a myth?

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