Subject: Re: [linux-audio-user] recording guitar interfacing
From: Paul Winkler (slinkp23_AT_yahoo.com)
Date: Thu Nov 29 2001 - 21:02:55 EET
On Thu, Nov 29, 2001 at 04:09:00PM +0100, Tobias Ulbricht wrote:
> But one more question:
>
> > But most of the better condenser mics require power to be provided
> > by the preamp. If the mic requires phantom power, it's probably
> > marked on the mic somewhere. This is called "phantom power" and
> > it's usually 48V DC. These mics cannot be connected directly to
> > your soundcard. You'll need a mixer or a standalone mic preamp
> ^^^^^^
>
> So any mixer that provides these "mic" inputs (usually they are, say track
> 7 and 8 of the 8-track-mixer??) provides the 48V DC current?
Not necessarily. Some low-budget mixers do not provide phantom
power. Example: the built-in mixer on most cassette 4-tracks; some DJ
mixers. If it has 1/4" mono phone plug mic inputs, it does not provide
phantom power. You need a balanced (3-pin) connector to get phantom
power to work. Most mixers with XLR mic inputs will have phantom
power, but be sure - ask before buying! Or look for a switch labelled
"Phantom" or "48V" or something like that. Usually, phantom power can
be switched on and off. Most inexpensive mixers have one switch that
controls phantom power on *all* mic channels.
> And still I could use these plugs for, say recording another two guitars
> (on top of the other 6 guitars on the remaining :) savely? Meaning the
> "phantom power" doesn't do any harm to any other audio source....?
I don't know how phantom power would affect a guitar. You shouldn't be
plugging a guitar into an XLR mic input anyway! If you're plugging the
guitar into a 1/4" line input on the mixer, it's not getting phantom
power, so don't worry about it.
here's a useful thread on possible phantom power damage:
http://groups.google.com/groups?hl=en&threadm=znr907108543k%40trad&rnum=4&prev=/groups%3Fq%3Dphantom%2Bpower%2Bmic%2Bdamage%2Bgroup%253Arec.audio.pro%26hl%3Den
Summary:
The only danger with phantom power is possible mic damage if you use
mics that aren't designed to handle it. Contrary to my previous post,
I've just been reading more about this and nearly all modern mics,
even ribbon mics, can handle 48V phantom power. Some old RCA ribbon
mics were originally wired in such a way that phantom power could
damage the ribbon.
The real problem is if you try to connect unbalanced mics or cables to
the balanced mic inputs. Any mic with an XLR connection is
balanced. But it can happen by accident if one of your cables has a
short circuit. So to be cautious, check your cables! When phantom
power is on, a short circuit in the cable could damage the mic, or
maybe even the mixer.
One other VERY IMPORTANT tip: for the safety of your mics, ears, and
other gear, do NOT plug in or unplug mics while phantom power is on.
When patching mics, *ALWAYS*
1) turn off phantom power
2) plug in or unplug mic
3) turn phantom power back on if needed
The reason is that the 3 pins of an XLR plug don't necessarily connect
at the same time, and there can be a very brief instant when the 48V
appears somewhere it's not supposed to. Two results:
1) an extremely loud POP sound.
2) If the mic contains a transformer (most do), the transformer could
get partially magnetized. The result is increased distortion in the
sound of the mic. It's possible to fix it by demagnetizing the
transformer but I'm not clear on how you would do this.
--paul winkler home: http://www.slinkp.com music: http://www.reacharms.com calendars: http://www.calendargalaxy.com
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