Phantom power always on?

[achabloop5080]

Hi guys,
I have a brand new Sound Devices USBPre 2 and I plan to use it on my next recital recordings....
I can switch on and off phantom powering through very little dip switch on the rear with a slender tool, but what if I leave phantom power always on?
Obviously I'd connect/disconnect xlrs only with the unit turned off, but when I turn on the USBPre 2 phantom power is already engaged....
Could it damage my wonderful Schoeps MK21g pair?
Any advice?
Thank you

[rcrowley]

It seems unlikely that there is any effective difference between powering up the USBPre2 with the phantom power turned on vs. turning on the phantom power when the USBpre2 is already powered up. And as you say, those little DIP switches are apparently not intended for everyday operational use, but only for configuration.

As long as you don't "hot-plug" the microphones with the USBPre2 ON, and phantom power ON, I wouldn't worry about it.

My first choice for operation would be to leave the phantom power switch on, plug in the microphones, and then turn the USBPre2 on.

[boojum]

I wrote Schoeps about hot connecting their mics. They do not recommend it but say it can be done. DPA does not seem to care. It is always safer to attach the mic and then enable the phantom power. I usually do it this way but have hot connected the Mk4's without damage, yet.

[Rolo 46]

P48 cannot damage microphones at XLR level connection
There is a very slight chance with say ribbons in a TRS jackfield.
T power will destroy ribbons and dynamics........

[Don S]

Although I try not to do this for the same reasons (Schoeps' recommendations), so far it has not given me a problem after happening. There might not be enough voltage to fry the preamps. Maybe some can elaborate?

[rcrowley]

Two possible problems with "hot-plugging" include...
1) Generating high-voltage "AC" from intermittent connections during the plugging cycle.
2) Briefly applying the 48V power to only one side of the balanced pair until both pins are mated.
Either of these could have a damaging effect on certain kinds of circuits. There are ways of mitigating these issues, but those methods may have undesired side-effects on the quality of the signal, so it is better to just avoid the whole issue.

[wwittman]

it's a complete non-issue

every major studio in the world had phantom on all the time and plugged in every conceivable type of mic with no problems

in an XLR all pins go in at the same time.


don't worry about it.
that's all you need to do.

[Jim Williams]

Yea, until something fries. They don't all seat at the same time, unless you mark time in seconds instead of milliseconds.

Yes, some rooms used to have phantom on all the time. It was a PITA for me. Once at Frank Zappa's Muffin Utility Research Kitchen we were jacking in some hot-rodded active guitars and basses (all of Frank's guitars were active).

I turned to Bob Stone and asked, "is the phantom on and if it is, can you switch it off"? He says, "no, it's on and can't be turned off".

Meanwhile, I'm fighting 48 volts jacking up the rear of the guitars, good thing I used 50 volt caps!

Everything here has an off switch. As it should. AE's were lazy back then...

many still are.

[joelpatterson]

In that case-- I'm just going to sit and wait until Bob Clearmountain says something.

[hbphotoav]

My only phantom-related problem involved bad cables and BeyerDynamic M500 ribbon mics and an inexpensive, small mixer. Cost me two factory rebuilds at about $160US each. Dynamics and condensers are much more likely to damage drivers in PA systems with the "pop" or "thump" that occurs when inserted into a unmuted, gained-up and potted-up channel. In a recording situation, unless ribbons and a bad cable are involved...

I'd still be aware and careful. But, then, I'm a conservative old so-and-so.

[sonare]

This certainly isn't "gospel" but this topic will arise and all the engineers present will say "ohhh-- that ISN'T a good idea." I then ask if they know of any actual problems as a result of NOT turning off phantom (not counting the big THUMP) and no one says a thing.

Rich

[TRJanuary]

I have personally witnessed condenser microphone damage from hot plugging phantom. (pins don't all make contact at the same time OR don't make contact at all due to dirt/corrosion/bad cable)

I wouldn't EXPECT it to happen alot, and obviously it doesn't happen very often or else we would be discussing it here, BUT it does happen.

I have also PERSONALLY witnessed the destruction of a Royer 121 ribbon by hot patching at a Bantam (TRS) patchbay with phantom present. If you even imagine to try to have any doubt about it, you are welcome to call Royer's service department because I know they deal with this everyday.

That's why mic patching is best left for XLR-only connections, but some old consoles have both Bantam mic patching AND per-channel switchable phantom, in order to help you avoid problems. They give you the rope, but they hope you are smart enough to not hang yourself.

[audioconsult]

Originally Posted by Don S

Although I try not to do this for the same reasons (Schoeps' recommendations), so far it has not given me a problem after happening. There might not be enough voltage to fry the preamps. Maybe some can elaborate?

hot pluging has only the risk that you damage your speakers when the channels are open..And the not so likely scenario that one of the xlr contacts is made way earlier than the other and so a high voltage difference between the + and - pin might damage some input circuit or magnetizing the I/O transformer..

So benefit of switching is that the voltage arrives at the same time at the mic and thats more likely that you are aware of open channels...

[huub]

We hotplug all types of microphones daily (neumanns, schoeps, sennheisers, DPAs, Coles although we obviously take care to not phantompower Coles).
Within our company, possibly hundreds of times per day. (Digitals desks are recalled, with phantom power on as this is saved in the setting, mics are patched later)
Our older trucks have jack patchfields (newer ones have ghielmetti, these do not potentially shortcut during patching).

I have never seen or noticed damage from hotpatching in twelve years.