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Old June 14th, 2008, 09:52 AM   #1
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Confused on "phantom" power

I know little more about electrical engineering than just enough to be handy around the house.

I have read what I can on phantom power but am confused. I see field mixers with only "A-B" or "Simplex Phantom" described as 12-18v power. I see phantom power units that run on 9v batteries and camcorders that have phantom power yet run on 7.2v batteries. And, some mics are self-powered with a 1.5v or 9v in the mic.

How can these lower voltage devices run mics that say they require 48v phantom power? Do those mics work on the mixers that only have 12-18v?

To be parochial about it, my Studio Projects B1 specs say it works on 4-48v but the glitzy-but-devoid-of-specifics R0de NTG-1 web page says just 48v. My intuition says 48v spec'd condensers will work just fine but there's a performance improvement when they have real 48v phantom.

So what's the deal?

TIA
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Old June 14th, 2008, 11:04 AM   #2
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Phantom power is one of those "rubber" specifications in the industry. Obviously, there has to be some voltage present for condenser mics to run. I've heard mention that some units provide only 12 volts as phantom power, while others give you the full 48 volts. It just depends on how conscientious the engineers were when they designed the phantom power supply.

Just because the camera or mixer runs off of 7.4 or 9 volts doesn't mean that's all you get for phantom power voltage. My Rolls mixer has a rather nifty circuit that takes the 12 to 18 volts DC it runs on and bucks it up to a regulated 48 volts for phantom power (I spent a lot of time crawling over the schematic to see how the mixer worked). Current requirements are in the milliamp range, so the phantom supply doesn't have to be too beefy.

A lot of mics can run either off their internal battery or phantom power. I've got an AKG C1000S that checks and switches off the internal battery when P-power is available. I notice that the "convertable" mics usually list two performance specifications, one when on battery and another for phantom power. Usually, the phantom power spec is a little better, so I run on P-power most of the time.

Hope that helps. The important thing is, does it sound good in your headphones?

Martin
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Old June 14th, 2008, 11:17 AM   #3
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Some of your questions are answered in this wikepedia article in the "Cautions" section:
http://en.wikipedia.org/wiki/Phantom_power

I am not an electrical engineer, but here are possibly correct short answers to some of your specific questions.

A mic powered by a battery is not using phantom power. The same mic may be capable of using phantom power, but the mic is using the battery it is using a different powering scheme. Some mics are wired to automatically switch circuits when phantom power is detected. Some mics should have the battery removed.

(Electret condenser mics are the ones that can use a battery. Even though some of these will also run on phantom power, the power is not being used to power the mic but rather a tiny amplifier. Regular condenser mics that need phantom power do not have an option to run on batteries.)

Different mics require different amounts of power. A mic that says it uses 4-48v phantom power will run on any voltage between these figures. Some big condenser mics require the full 48v (or 52v, see the last link below).

A professional mixer will output full 48v power. Small devices that advertise 48v phantom power sometimes don't output the full 48v. For example, the Microtrack says 48v but actually has about 32v (if I remember correctly). It will run most mics, but not some larger ones.

Powered mics with a 1/8" stereo plug are not using phantom power but a special power scheme.

Simplex power is another name for phantom power. See the 3rd paragraph in this recent article:
http://psbg.emusician.com/ar/emusic_...ower/index.htm

If a mixer says it outputs 12-18v, that is all it means... that it will only run mics that will run on this amount of power.

The standard for phantom power is 48v, but systems will output less. the Phantom refers to the way the power is sent up the cable, not necessarily the voltage, despite the standard.

As you will see in the wikipedia article, another powering scheme is T-power, though not used much at all any more.

A box that outputs phantom power but uses, say, a 9v battery, simply transforms the output to 48v (or 52v, see link below). Some of these are high quality and output enough power at the correct voltage and some aren't. (Same with mixers... the cheaper mixers are not going to necessarily have the correct voltgage nor ecnogh mA power.)

Here is a link with a short explanation and links to several portable phantom power supplies:
http://www.core-sound.com/2Phant/3.php

In general, mid to high end standard professional equipment will all work together without issue.

Mid to low-end eqipment needs to be tested in the the configuration to be used.

Certain high end and/or large mics will require accurate maximum voltage and a high mA output from the phantom power supply.
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Old June 14th, 2008, 11:24 AM   #4
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Note: A-B, Simplex, or T-Power are NOT the same thing as phantom power and conceivably even damage microphones that are wired for phantom. Vice versa, a T-Power mic like the Sennheiser MKH416T model cannot be powered by a phantom power source without the intercession of an adapter. A-B or T-Power is especially disasterous if you accidently plug a dynamic mic into it!

Some mics require full 48v phantom, other work fine with less. One of the factors is whether the capsule uses a permanently charged "electret" diaphram and the external power is only used to run the internal electronics, or is a "true condensor" type that charges the diaphram as well as runs the electronics from the external power source. Each input on my own mixer (SD442) is switch selectable to provide either phantom, T, or none mic power while the phantom supply itself is selectable for either 12volt phantom to conserve battery power or full 48volt when one or more of the connected mics requires it (supplying 48volt phantom to a mic that only needs 12volts is safe, just wastes battery juice.)
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Old June 14th, 2008, 11:46 AM   #5
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Quote:
Originally Posted by Steve House View Post
Note: A-B, Simplex, or T-Power are NOT the same thing as phantom power and conceivably even damage microphones that are wired for phantom. Vice versa, a T-Power mic like the Sennheiser MKH416T model cannot be powered by a phantom power source without the intercession of an adapter. A-B or T-Power is especially disasterous if you accidently plug a dynamic mic into it!
I believe this article explains this clearly:
http://psbg.emusician.com/ar/emusic_...ower/index.htm

Phantom power is also sometimes known as Simplex power. Simplex and Phantom are the same. Simplex might be seen in relation to an older battery powered mixer that supples only 12v or 24v, or even only 12v and 18v.
However, T Power, also known as A-B power is quite different. If this power is applied to non-T power mic, damage can be done.

On new equipment these days, T power is usually only encountered at the high end, such as Sound Devices products. They offer both T power and 48v Phantom power. Professional equipment from other makers also offer both T-power (A-B power) and phantom power.
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Old June 14th, 2008, 01:29 PM   #6
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Got it. Transformers. Right.

So the Studio Projects b1 (4-48v) will work but probably not the R0de NTG-1 (48-52v)?
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Old June 14th, 2008, 01:44 PM   #7
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Quote:
Originally Posted by Jack Walker View Post
...
Phantom power is also sometimes known as Simplex power. Simplex and Phantom are the same. ...
Thanks for the correction - senior moment as I typed :)
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Old June 14th, 2008, 01:49 PM   #8
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It appears that the Studio Projects B1 mic requires 48v phantom, plus or minus 4 volts (48 +/- 4V.):
http://www.bhphotovideo.com/c/produc...icrophone.html

The Rode NTG-1 specs are exactly the same -- 48v phantom, pluse or minus 4 volts (+48 V phantom, 44V to 52V):
http://www.bhphotovideo.com/c/produc...icrophone.html

Both mics should require a reasonable milliamp level of power.

Therefore, a phantom power supply that meets these specs (which should be anything mid-level and higher) should work fine for both mics. Your basic XH-A1 or similar camera should also work.

If you're looking at the B1 you might also look at the AT2020:
http://www.bhphotovideo.com/c/produc...icrophone.html
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Old June 14th, 2008, 01:54 PM   #9
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Actually, I was looking at the mixer end, a Shure FP31 and wondering of it would work with my condenser mics. The FP31 specs only A-B and "Simplex" 12-18v phantom. And, it's applied to all inputs set to mic level.

Last edited by Les Wilson; June 14th, 2008 at 04:48 PM.
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Old June 15th, 2008, 01:49 AM   #10
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Quote:
Originally Posted by Ernest House View Post
Actually, I was looking at the mixer end, a Shure FP31 and wondering of it would work with my condenser mics. The FP31 specs only A-B and "Simplex" 12-18v phantom. And, it's applied to all inputs set to mic level.
This type of mixer is what's talked about in the emusician.com link I referenced above.

A-B is T power, not what you want to use as it can damage microphones.

Simplex is regular Phantom power, however, the mixer you have is at a voltage much less than the specs for the mics you referenced. Contrary to your first post, the B1 is not 4-41, but rather 48volt, plus or minus 4 volts.

If you haven't read it, read the emusician short article. It specifically covers exactly what you are asking about in a very clear way.
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Old June 15th, 2008, 06:00 AM   #11
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Yes. I had read the article and bookmarked the site. It's a nice resource.
http://psbg.emusician.com/ar/emusic_...ower/index.htm

The article spends a lot of words explaining T-power and Phantom power but I left it remembering this:
"Because no real standards exist for implementing phantom power in mixers, it is almost impossible to know what products will work together reliably. Unfortunately, microphone manufacturers do not provide a list of compatible products, so there is no way to know for sure. You simply need to plug in the mic and try it."

But I went back to it after your post and found this:
"Most contemporary condenser mics will work with phantom power voltages from 9 to 54 VDC. These mics include an internal power regulator that makes the mic operate successfully at whatever voltage you give it."

Thanks.
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Old June 15th, 2008, 06:46 AM   #12
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Dear Ernest,

Many microphone manufacturers list their phantom power requirements.

For example, for many Neumann microphones they specify 48 volts, + or - 4 volts. So they work with 44 to 52 volt phantom power.

I have seen specifications for other microphones listing 12 to 52 volt phantom power.

I would be careful since a lot of phantom powered microphones will not work properly with voltages as low as 9 or 12 volts. In other words, supply the voltage that manufacturer specifies.
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Old June 16th, 2008, 04:10 AM   #13
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Quote:
Originally Posted by Jack Walker View Post
On new equipment these days, T power is usually only encountered at the high end, such as Sound Devices products. They offer both T power and 48v Phantom power. Professional equipment from other makers also offer both T-power (A-B power) and phantom power.
Most SHURE mixers going back a number of years have AB / T as well as Phantom, but if you're looking for a new mixer, I'd get one from Sound Devices.

Regards,

Ty
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Old June 16th, 2008, 04:41 AM   #14
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Make sure you read the caution section of the wiki article closely. Especially the part that talks about current draw. On most on-location/field microphones, current isn't too much of an issue. However, I have been bitten by trying to get multiple studio microphones powered by a device because it didn't support as much current draw as the microphones required. The phantom power spec allows for 10 mA and some microphones want all of that (Earthworks in particular), if you hook up 4 microphones, suddenly you have 40 mA of current you're drawing from the source. Some devices simply can't handle that type of current draw.

So while voltage is important, make sure you also look at the other side of the power equation, which is current draw.

Wayne
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Old June 20th, 2008, 07:34 PM   #15
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This is a followup to say that both the NTG-1 and Studio Projects B1 mics work fine with the Simplex power from the Shure FP-31. I experimented with recording high levels and both mics performed without distorting even when the mixer reading went into the +1 and +2 range. I have much to learn. Should be fun. A big thanks to everyone here.
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