Phantom Power Filtering (removal of phantom power)...

Archived from groups: rec.audio.pro,rec.audio.tech (More info?)

Hey Everyone. I can't seem to find the answer and/or product to
satisfy my needs: a phantom power filter/remover.

I have a ribbon mic I'd like to gig with, and the PA systems we use
normally plug into have an all-channels-on/off for the phantom power.
Our vocalist uses a condenser mic, so she needs it on. If the phantom
power hits my ribbon mic, it might permanently damage the ribbon
element.

Does anyone know of a DIY homebrew solution?

Thanks,
Chris

Archived from groups: rec.audio.pro,rec.audio.tech (More info?)

"Chris Breitner" <chris_breitner@hotmail.com> wrote in message
news:ba4f639a.0406301644.1d98dd6@posting.google.com...
> Hey Everyone. I can't seem to find the answer and/or product to
> satisfy my needs: a phantom power filter/remover.
>
> I have a ribbon mic I'd like to gig with, and the PA systems we use
> normally plug into have an all-channels-on/off for the phantom power.
> Our vocalist uses a condenser mic, so she needs it on. If the phantom
> power hits my ribbon mic, it might permanently damage the ribbon
> element.
>
> Does anyone know of a DIY homebrew solution?

Two options :
1:1 Isolation Transformer - The better Transformers usually cost more and it
is not difficult to spend $100 on a decent Transformer ...

Capacitors in Series with the Signal - 47uF is usually adequate but can
depend on the input impedance of your mixing desk - typically 1K or so which
will give you low Frequency rolloff with a -3dB point of 3Hz Of course the
Desks internal Decoupling Caps will be in Series with this so this will
probably raise your -3dB point to 7 Hz or so.

D Pin 2 ---------------||--------------- Pin 2 of the Mic
e +ve
s Pin 3 ---------------||--------------- Pin 3 of the Mic
k Pin 1 ------------------------------ Pin 1 of the Mic

Arent Ribbon Mics a bit delicate to take on the road ???




Regards
Richard Freeman

Archived from groups: rec.audio.pro,rec.audio.tech (More info?)

Chris Breitner wrote:

> Hey Everyone. I can't seem to find the answer and/or product to
> satisfy my needs: a phantom power filter/remover.
>
> I have a ribbon mic I'd like to gig with, and the PA systems we use
> normally plug into have an all-channels-on/off for the phantom power.
> Our vocalist uses a condenser mic, so she needs it on. If the phantom
> power hits my ribbon mic, it might permanently damage the ribbon
> element.
>
> Does anyone know of a DIY homebrew solution?
>
> Thanks,
> Chris
If its your board, go into one of the channels and remove the two
phantom resistors from the channel you want to use the ribbon on.
It will just cost you some time (if you know what your doing that is)

Otherwise, a good isolation transformer as some else suggested externally

Bob




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Archived from groups: rec.audio.pro,rec.audio.tech (More info?)

On Wed, 30 Jun 2004 17:44:19 -0700, Chris Breitner wrote:

> Hey Everyone. I can't seem to find the answer and/or product to
> satisfy my needs: a phantom power filter/remover.
>
> I have a ribbon mic I'd like to gig with, and the PA systems we use
> normally plug into have an all-channels-on/off for the phantom power.
> Our vocalist uses a condenser mic, so she needs it on. If the phantom
> power hits my ribbon mic, it might permanently damage the ribbon
> element.
>
> Does anyone know of a DIY homebrew solution?
>
> Thanks,
> Chris

You could use a battery phantom power supply box for this.
It may sound silly, but if it's off and has no batteries in it, it should
just block the dc and pass the mic signal.
You should check with a meter, just to make sure.

Archived from groups: rec.audio.pro,rec.audio.tech (More info?)

"Logan Shaw"
>
> Someone will, I hope, correct me if I'm wrong, but couldn't you just
> lift the ground and go with a floating ground? The potential is between
> pin 1 (the ground) and pin 2 and between pin 1 (the ground) and pin 3.
> There is no potential between pins 2 and 3 because there are equal
> value resistors between them and the +48V of the phantom power.
>
> I'm assuming, of course, that cutting the ground near the mic will
> still provide you with adequate noise shielding, etc.
>


** Why don't you try out your own idea and check your assumption ???






............... Phil

Archived from groups: rec.audio.pro,rec.audio.tech (More info?)

One possibility I didn't see presented is a separate mic pre for the ribbon,
which then goes into the line in rather than through the mic input. There
are a couple of "buy it now" Studio Projects VTB1s on ebay right now for
$129. Not an un-useful purchase anyway, and it easily fits your
requirements.

http://cgi.ebay.com/ws/eBayISAPI.d [...] 30779&rd=1

--


Roger W. Norman
SirMusic Studio

"Chris Breitner" <chris_breitner@hotmail.com> wrote in message
news:ba4f639a.0406301644.1d98dd6@posting.google.com...
> Hey Everyone. I can't seem to find the answer and/or product to
> satisfy my needs: a phantom power filter/remover.
>
> I have a ribbon mic I'd like to gig with, and the PA systems we use
> normally plug into have an all-channels-on/off for the phantom power.
> Our vocalist uses a condenser mic, so she needs it on. If the phantom
> power hits my ribbon mic, it might permanently damage the ribbon
> element.
>
> Does anyone know of a DIY homebrew solution?
>
> Thanks,
> Chris

Archived from groups: rec.audio.pro,rec.audio.tech (More info?)

"Logan Shaw"
>
> Someone will, I hope, correct me if I'm wrong, but couldn't you just
> lift the ground and go with a floating ground? The potential is between
> pin 1 (the ground) and pin 2 and between pin 1 (the ground) and pin 3.
> There is no potential between pins 2 and 3 because there are equal
> value resistors between them and the +48V of the phantom power.

When this is actually the case, there's no problem at all using phantom
power with a ribbon. The reason it can be a problem (aside from mikes
with center ground taps on the transformer secondary) is that sometimes
those resistors are not very equal values. I'm not going to mention any
particular brand of mixers, but suffice it to say that some of the cheaper
ones out there don't match the supply resistors very well. This also badly
degrades common mode rejection as well as making for an issue with dynamic
mikes.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Archived from groups: rec.audio.pro,rec.audio.tech (More info?)

Chris Breitner <chris_breitner@hotmail.com> wrote:

> Hey Everyone. I can't seem to find the answer and/or product to
> satisfy my needs: a phantom power filter/remover.
>
> I have a ribbon mic I'd like to gig with, and the PA systems we use
> normally plug into have an all-channels-on/off for the phantom power.
> Our vocalist uses a condenser mic, so she needs it on. If the phantom
> power hits my ribbon mic, it might permanently damage the ribbon
> element.
>
> Does anyone know of a DIY homebrew solution?

You've gotten plenty of good advice so far, but the one thing barely
mentioned is that besides a center-tapped output transformer, a
defective microphone cable is just about required in order for phantom
power to damage a ribbon mike. So buy yourself a nice $25 mike cable
that's a different color than all your other mike cable. Treat it
gingerly and label it "only for XXX ribbon mike." Don't let anybody
step on it, tug on it, tie it in knots, or run it over with a rack full
of heavy equipment. This will cost a heck of a lot less than a good
isolation transformer.

ulysses

Archived from groups: rec.audio.pro,rec.audio.tech (More info?)

George Perfect wrote:

> In this place, Justin Ulysses Morse was recorded saying ...
>
>> My BK-5's are less delicate than my girlfriend by a wide margarine.

> (BTW - just how wide IS a margarine?)

From what I understand, margarine is really fat.

- Logan

Archived from groups: rec.audio.pro,rec.audio.tech (More info?)

Bob Cain <arcane@arcanemethods.com> wrote:
>Scott Dorsey wrote:
>
>> The reason it can be a problem (aside from mikes
>> with center ground taps on the transformer secondary) is that sometimes
>> those resistors are not very equal values.
>
>How does this cause a problem (other than the rejection
>issue)? If the same supply is presented to each side, and 1
>is open, then current won't flow between 2 and 3 regardless
>of the mismatch.

I didn't word that very well at all. If there _are_ center ground taps,
there is a ground path to pin 1, and therefore the imbalance is an issue.

In fact, even with the ground tap, if there are precise enough resistors
and a good enough transformer, it's a non-issue.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."