question:phantom power on dynamic mics
Dennis Liu
phantom power switches on pre amps? Why not just have them on all the time?
E mail reply THANKS
Rob Hoffman
It will usually kill Ribbon mics and I've seen a few dynamics die when
48v was applied, my sennheiser 441 is one of them.
Rob
Rob Reedijk
: Dennis Liu wrote:
: >
: > Will phantom power on a dynamic mic hurt the mic? If not why do people put
: > phantom power switches on pre amps? Why not just have them on all the time?
: > E mail reply THANKS
: It will usually kill Ribbon mics and I've seen a few dynamics die when
I think that usually it won't. But it always pays to practice safe connex
when it comes to ribbons, just in case.
: 48v was applied, my sennheiser 441 is one of them.
Now THAT's surprising. Wow. Did you ever figure out why.
Rob R. (another Rob, but of a member of the BORs (Brotherhood of Robs))
soundguy@.ix.netcom.com
<dliu...@email.msn.com> wrote:
>Will phantom power on a dynamic mic hurt the mic? If not why do people put
>phantom power switches on pre amps? Why not just have them on all the time?
>E mail reply THANKS
>
Won't hurt the modern, run of the mill dynamic(58,88,112,421,etc), but
they'll make a hell of a pop if you unplug them with the channel up.
(on a 100,000 watt P.A. , you can give someone dain bramage...)
Patrick
soun...@ix.netcom.com
MTALANCA
Dennis,
Phantom power is to run condenser mics instead of buying batteries for them
all the time. And no, a regular dynamic mic will not suffer any problems if you
engage the phantom power but they don't require it. Now if you have a ribbon
mic and switch phantom power on it it will destroy the mic. thats why theres a
switch on the pre. To use phantom power when you need it. Hope this helps
Sincerely
Mike Talanca
MTal...@aol.com
Monte P McGuire
Dennis Liu <dliu...@email.msn.com> wrote:
>Will phantom power on a dynamic mic hurt the mic? If not why do people put
>phantom power switches on pre amps? Why not just have them on all the time?
Most modern mikes can tolerate 48V common to pin 2 and 3, so it's not
such a danger anymore. The few old dynamic mikes that can't handle it
can usually be modified easily so that pin 2 and 3 are floating
w.r.t. pin 1. Of course, a bad cable with a short from pin 2 or 3 to
pin 1 will cause problems, but that's an avoidable situation most of
the time.
The reason for the switch is that it's a _really_ bad thing to plug
many mikes into a phantom powered preamp while P48 is on. While pin 1
usually connects first with most available XLR connectors, pin 2 and
pin 3 do not connect simultaneously. If the mike does not float pin 2
or 3 relative to pin 1 (as is the case with all transformer output P48
mikes), you can send a brief pulse of current through the output
transformer secondary, and that can somewhat partially magnetize it,
increasing distortion.
A similar but much less significant effect can happen with a dynamic
mike; a tiny current pulse will be caused as the first pin 2 or pin 3
connection charges up the other pin's cable capacitance through the
mike's transformer or voice coil. This is not such a big deal with a
moving coil dynamic, but with a ribbon, the resulting mechanical
movement of the ribbon could be damaging. It's not likely, but with a
ton of cable or a really long snake, maybe it's a big deal. Who wants
to risk it right before you're trying to use the mike though...!
The moral of the story: if you want to be completely safe, switch off
P48 before connecting mikes, especially P48 powered condensers. If
you use only moving coil dynamics, don't worry and leave P48 off
anyways.
It's for this reason that I find it's simplest to avoid P48 condensers
for live PA, unless you have a well maintained system with good cables
and there's no chance of beer getting in the snake or on the cables.
I once mixed a band in a club where one of the stages was directly
below the upper floor's bathroom. 12 hours into the festival, the
bathroom flooded, and so did the stage and snake. For some stupid
reason, P48 was left on by the guy who started the show and when it
came to my set at the end of the night, it created quite a bit of
havoc with the dynamic mikes on stage. Shorting pin 2 or 3 or both to
pin 1 is not a good thing! I did the show with the 2.5 mikes that
still worked... :-(
Regards,
Monte McGuire
mcg...@world.std.com
Mike Rivers
> It will usually kill Ribbon mics and I've seen a few dynamics die when
> 48v was applied, my sennheiser 441 is one of them.
Here's a second opinion.
It will do no damage if the mic and cable are properly wired, that
there's no short between ground (Pin 1) and either of the hot leads.
The story about phantom power damaging ribbon mics stems from the
original configuration of the RCA 44 (maybe the 77, maybe both) having
an input transformer with the center tap grounded. This shorted out the
phantom voltage, causing a ribbon-popping transient in the process. Any
RCA mic that's in studio use today will have had the center tap of the
transformer lifted, but it never hurts to check if you're using the mic
for the first time.
The reason why there's a switch is so that you can turn it off when you
don't need it and be absoulutely sure you won't blow something. There
have been instances where a device with an unbalanced output has been
plugged into a powered input, causing damage to the device, but that's
pretty rare.
------------
I'm really mri...@d-and-d.com (Mike Rivers) On the road.
Somewhere east of Lost Angeles and west of the moon
Anahata
>you can send a brief pulse of current through the output
>>transformer secondary, and that can somewhat partially magnetize it,
>>increasing distortion.
>
Could be years though the magnetization will be slight. I guess it
could be demagnetized by applying a large AC signal that decayed to zero
in a few seconds, like a degaussing coil.
>Can you leave condensers that use P48 plugged in when you first turn
>the power on without damaging them?
>
If I understand you correctly, that is what you should always do. Plug
in first, turn on power second. A P48 switch is a way of achieving the
latter without having to power down the whole desk...
Anahata
ana...@freereed.demon.co.uk + http://www.freereed.demon.co.uk/
ana...@locust.co.uk email to mobile phone 8 line messages max
0171 638 5577 (W) 0171 229 6076 (H) 0976 263827 (mobile)
Monte P McGuire
>>In article <Oi3t2u2...@upnetnews02.moswest.msn.net>,
>>Dennis Liu <dliu...@email.msn.com> wrote:
>>
>>you can send a brief pulse of current through the output
>>transformer secondary, and that can somewhat partially magnetize it,
>>increasing distortion.
>
>How long does this magnetization last?
It can go away over time by running signals through the transformer
(i.e. by operating the mike) or you can manually demagnetize the
transformer by applying a slowly ramped up and then ramped down sine
wave to a winding, sort of like how you degauss a tape machine head.
One way to tell if a transformer has been magnetized is to measure its
second harmonic distortion level. Ideally, a transformer has only
third harmonic and it'll produce second harmonic only if there is DC
on a winding or if the core is magnetized. Personally, I have not
gone through my mikes and found if any are damaged, but it sounds like
a good thing to do every few years, especially if you use them in less
than ideal situations.
>Can you leave condensers that use P48 plugged in when you first turn
>the power on without damaging them?
Yes, if you make all the connections with the board or preamp powered
down and then turn it on, it's completely safe, since phantom will be
applied to both pin 2 and pin 3 simultaneously.
Regards,
Monte McGuire
mcg...@world.std.com
Roger W. Norman
accidentally have phantom power applied, but who uses unbalanced mic cables?
<g>
Roger W. Norman
MTALANCA wrote in message <19980929221246...@ng76.aol.com>...
Mike Rivers
> Well, you can fry a dynamic mic if you use an unbalanced cable and
> accidentally have phantom power applied, but who uses unbalanced mic cables?
> <g>
1. Anyone who's ever had a cable short between one of the conductors and
the shield. Good cables rarely fail if taken care of, but shorted
cables aren't uncommon in road touring systems.
2. People who say "I want to make my own cables but I don't know much
about soddering (sic). Can anyone tell me how to wire them up?"
3. Sometimes they come that way from the factory.