Adapting a microphone to remote phantom power

On 4/12/2009 4:13 PM Dave Plowman (News) spake thus:

You keep saying this, which doesn't make it any more or less true.

Can you quote a reliable, authoritative source that defines phantom power so? (And puleeze, don't even *think* about using Wikipedia!) One which says that phantom power (R)(TM) *must* include the use of balanced inputs, etc., as you've been claiming?

If there exists such a definition online, that could settle the whole matter pretty easily.

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On Sat, 11 Apr 2009 11:41:30 -0700, David Nebenzahl put finger to keyboard and composed:

I was curious as to what a microphone manufacturer had to say.

For example, Shure considers that "phantom power" and "bias" are two different concepts:

Sennheiser also appears to differentiate between phantom power (48V) and T or A-B power (12V):

And then there's this site:

Phantom power now appears to be defined by a prevailing standard, DIN EN 61938, July 97, formerly DIN IEC 268-15 and DIN 45 596.

That said, I'd always used the terms "phantom power" and "bias" interchangeably, but my knowledge of microphones is essentially zero.

There are other systems where power is supplied to the remote device via the signal cable, eg a masthead amp, or a video camera, or an LNB for a satellite dish. I think these are generally referred to as being

*line* powered. Instead of a resistor, the series element is an inductor. This has a low impedance at DC, or AC mains frequency, but a high impedance at video frequencies.

Then there are those devices which can be considered to be *signal* powered, eg serial mice which rob power from the DTR and RTS signals (?) of an RS232 port.

So I guess the moral of the story is that one has to be aware that not everyone speaks the same language, whether or not they are correct. However I'd tend to lean towards a definition that is incorporated into an accepted standard. Unfortunately DIN/EN 61938 does not appear to be available as a free download. :-(

The funny thing is that telephones can be considered to be phantom powered, yet I'd never heard the term used in that context until I read the Wikipedia article on the subject.

- Franc Zabkar

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I get some 197,000 hits when I Google for phantom power. And can't be bothered wading through all of them.

Lets just say it's an album from Super Furry Animals if Google is your source of things technical.

I've a feeling if I gave you such a site you'd just rubbish it as you do Wikipedia if it doesn't agree with you.

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    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

That explains things pretty well.

As does that - although it only talks about one other version of line powering, T or AB, which is again a defined standard as it's dealing with basically pro mics. Many mics (especially on consumer goods) use a different line power voltage to the 12 volts of T power, as it's only usually to power an FET etc to do impedance matching.

That appears pretty definitive.

Anywhere that sold phantom powered mics would require you to know what they were when buying, otherwise you might end up with one which didn't work to your requirements.

Indeed.

No - telephones are line powered. True phantom power was however first used in the telephone industry for other purposes.

A telephone line is balanced - but if you apply an AVO to that line you'll see the DC. Do the same to a balanced mic line with phantom power present and you won't.

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    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

Then you don't know how to properly connect anything to the phone line, other than a cheap imported telephone.

Powering a microphone isn't rocket science, no matter how much you try to build it up. So what if the DC is applied to both sides of a balanced microphone circuit. that was done to prevent morons from frying a dynamic microphone by using it with the wrong equipment. Trying to idiot proof simple technology is no big deal, till they breed bigger and bigger idiots who have ego problems. A modern design would use RF on the line to eliminate any possible hum, and be high enough that it couldn't interact with the audio. That wasn't possible with early phantom mics, using tube preamps. The same tube preamps that like to break into oscillation at times, or became microphonic.

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Could you take me through that statement step by step?

Thanks for confirming you know nothing about the use of microphones. I suppose you'd have dozens of different connectors on each channel input to satisfy your 'military spec' attitude? And dozens of different cables to go with those?

You certainly know about that.

You get hum from DC?

Given any thought to cable design? And the lengths those often are? Over a mile is common.

Dunno where you got the idea of *early* phantom mics being tube. If there were any they weren't in common use. The first mainstream phantom power mic was the Neumann KM 84. And it wasn't a tube mic. Previous condenser valve mics used individual power supplies via multicore cable. With all the problems that caused in a large rig.

I suppose you only came across broken ones. In practice, oscillation was rare. With good makes, of course.

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    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

Why, you still wouldn't get it.

YAwn. Thanks for proving nothing.

Sigh, you are more than brain dead. WTF would the military intentionally shoot themselves in both feet? What part of 'specification' don't you understand? There were three types of connectors. XLR, terminal blocks and patch bays. Everything except the magnetic phono circuits and headphone jacks were balanced. Obviously you know nothing about the reasons the military uses standards.

Its confirmed with every idiotic post you make.

It can be picked up on a DC circuit. Why do you think they use HF AC to power the lamp used in film projectors, instead of DC? Its easier to rectify & filter a power source well above the needed audio bandwidth, than deal with electrical noise is some locations. try your DC power in places near a substation, where the AC magnetic field can affect video monitors, or a high power transmitter causes ingression problems. No circuit is a perfect balance in those situations.

Yawn. At a mile I would look into fiber or an RF link. Try running a mile of audio cable in a place with a lot of lighting is sheer stupidity. I had a lightning strike at my last house. It hit the buried phone cable and vaporized the copper in 1.2 miles of buried, shielded six pair cable. then it wiped out the subscriber interface circuit for mine, and 15 other houses and destroyed the copper pair back to the central office.

I had a T studio building hit by lightning as well. it blew out chunks of concrete, and wiped out our computer network, 11 GHz STL and four C-band LNBs, most of the satellite receivers and the 1A2 telephone system I replaced a lot of damaged wire.

There are some records that were released with the mics acting up. Of course, you don't know what I'm talking about.

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You can\'t have a sense of humor, if you have no sense!

On Mon, 13 Apr 2009 09:14:18 +0100, "Dave Plowman (News)" put finger to keyboard and composed:

I confess I'm ignorant about professional audio gear. I've always thought of phantom power as a generic term, and it appears that many people do likewise.

In fact the Wikipedia article recognises this:

===================================================================== The low-current 3 to 5 V supply provided at the microphone jack of some consumer equipment, such as portable recorders and computer sound cards, is sometimes called "phantom power." =====================================================================

I can see a parallel in the definition of USB standards:

===================================================================== Because the USB 2.0 Specification encompasses all USB data transfer speeds, low (1.5Mb/s), full (12Mb/s) and high (480Mb/s), it is important that vendors clearly communicate the type of product on packaging and in marketing and advertising materials. Inconsistent use of terminology in combination with the existing general misconception that USB 2.0 is synonymous with Hi-Speed USB ... creates confusion in the marketplace. =====================================================================

One would think that low, full, and high speed are loose, generic terms, but in the USB context they have particular numbers associated with them.

OK, I see now ...

- Franc Zabkar

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That'll be a no, then.

If you even gave it a modicum of thought you'd realise the ability to have one connector and type of cable for virtually any microphone has real benefits. But then thinking beyond the end of your limited experience isn't your strong point.

I'd have said it being picked up on the actual audio output to be more of a problem, wouldn't you? If you ever thought before typing.

Think you'd be better telling the mic makers that. I'm sure they'd be grateful for your original thinking. After all they don't have a single decent engineer between them...

You might well look into it. Of course you wouldn't be funding it...

Is this called thread drift? Or just the effects of alcohol?

All with fibre optic I assume? Wouldn't be a problem to one of your talents.

All of them?

I doubt if even you do.

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    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

Seems there may well be lots of people who use the term without knowing what it means.

Yes. Wonder who added that to the original article?

Not sure it's quite the same. There is some compatibility in certain combinations between the various USB devices. There is none between line and phantom power.

That's not the best of explanations. Phantom power is distributed from a central PS to the mixer inputs via standoff resistors. Which limit the amount of current available to any single mic. Necessary to prevent a line or mic fault bringing down the entire supply.

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    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

Read

bitch at

others.

Irrelevant. The term is regularly abused. I have explained in considerable detail why it's a no-go and still you whine.

Graham

That is the term I would use too. It is NOT phantom power'.

Graham

Classic 'dumbing down'.

Graham

I'm not aware of any tube based condensor mics that used phantom power as we talk of it now. They usually had dedicated multipole connectors rather than the now ubiquitous 3 pin XLR.

Graham

On 4/13/2009 3:36 PM Dave Plowman (News) spake thus:

You can easily find out: just check the "history" tab and trace it back. (But it'll probably turn out to be an "anonymous IP", meaning that it could be anybody, qualified or not.)

And there's really no such thing as an "original article" on Wikipedia, as all articles are constantly undergoing rewriting for better or worse (often the latter).

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Save the Planet
Kill Yourself

- motto of the Church of Euthanasia (http://www.churchofeuthanasia.org/)

Rather obvious when you think of the technology then - and the restricted current available with phantom power.

There's been quite a revival in valve mics and I've a feeling there may be at least one which runs off phantom. But the majority still use a dedicated PS and multicore cable.

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    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

Well you can take it from me the current explanation is pretty decent and rather better than many others you'll find.

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    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

Yup, I've seen a few. Usually the PSU is finished in that Hammerite style paint in a silver grey.

Graham

I've amended the entry slightly to make it clearer.

Graaham