Talk:Phantom power

Standards

The IEC 61938 Standard defines 48-volt, 24-volt, and 12-volt phantom powering.

The signal conductors are positive, both fed through resistors of equal value

(6.81 kΩ for 48 V, 1.2 kΩ for 24 V, and 680 Ω for 12 V), and the shield is ground.

Can someone provide a reference for: 1.2 kΩ for 24 V? Where does this come from? I can't find any reference to this... — Preceding unsigned comment added by 176.147.175.24 (talk) 08:27, 22 October 2018 (UTC)

I know that the phantom power standard (whatever that is) specifies 6.8k resistors between the 48 V supply and the (XLR) pins. As here:

http://www.uneeda-audio.com/phantom/phan03.gif

This could be specified, maybe with a circuit. It is not always adhered to, however.

Also, there is a "standard" for the mic load, which is 9k between pin 1 and the others, and 200 ohm between 2 and 3. However, I have no idea where this standard comes from and I am sure it is not widely used. Just what I was told to use. Maybe it is just a standard test load. But anyone who wants to search these and write about them should. - Omegatron 17:42, Mar 2, 2004 (UTC)

Can you provide a reference to any such standard? I don't know about it. Altaphon (talk) 20:58, 7 March 2011 (UTC)

The schematic drawing is wrong, I will provide a corrected one soon. There should never be an R3, this is commonly done by some makers to eat some power supply hum but there is no substitute for a clean, low impedance +48 feed. Altaphon (talk) 21:01, 7 March 2011 (UTC)

The statement about P24 vs. P12 and P48 has it exactly backwards; P24 is deprecated, not the others. I will try to update this information from the latest version of the standards.DSatz (talk) 10:05, 1 February 2019 (UTC)

Rewrite

Major rewrite. To be done: add references to the IEC standard (EN 61938) and DIN 45596. Also if anyone can improve the style and/or add the usual Wiki cross-references, great. I'm kind of new at this. DSatz 13:46, May 8, 2005 (UTC)

I did some of this. In the meantime the IEC standard has been revised, have corrected the references to match the new version. Altaphon (talk) 23:09, 4 June 2015 (UTC)

Origin

Someone added the claim that Neumann (= Georg Neumann GmbH, Berlin) invented phantom powering in 1966. That is indeed the year of Neumann's first phantom-powered microphones (the KM 83, KM 84 and KM 85) according to Neumann's history chart (see http://www.neumann.com/infopool/download.php?Datei=docu0051.PDF) and other sources. It may well be that Neumann introduced 48-Volt phantom powering.

But the article also mentions a system used by French radio somewhat prior to this time, with 9 - 12 Volt phantom powering and a positive circuit ground. Nagra analog tape recorders, including my IV-S right ... here ... (stretching) ... supported this "negative phantom" powering system, which matched the positive ground power supply of the Nagra itself. To my knowledge the first studio microphones made for that system were the Schoeps CMT 2-- series (CMT 24, 25, etc.). I have a schematic for their circuit dated July, 1964, but the company says that the microphone itself was introduced only in 1965. I haven't been able to resolve that difference yet (Schoeps never kept such good historical records, unfortunately).

At any rate it seems clear that Neumann adapted this powering method to what eventually became its most popular form, but they didn't invent it. DSatz 22:13, 29 October 2005 (UTC)

I came here to say the same this. I can find no reliable source on this: everything I see online is clearly citogenesis. I believe the information about the origins should be removed. 47.55.126.103 (talk) 04:52, 27 December 2023 (UTC)

I really think someone should look more closely into the origins of phantom. I personally own two phantom powered schoeps microphones that pre-dates the KM84.

Also, the sentences about a auxilliary 48 volt system at the norwegian broadcasting is as far as i can tell unfounded speculation from Neumann. The consoles in use there at that point was to a large degree built by Kongsberg Vaapenfabrikk( http://www.kongsberg.com/nor/kog/ ), the powersupplies might have been 48volts so the misunderstanding might come from there. And even though it is dark in the winter, i would suggest that normal 220Volt electricity where used for lighting purposes:-) They did however adapt the use of american cannon/xlr connectors early on togheter with the BBC, so the misunderstanding might stem from this. KM84 serial no. 34 is atleast a cannon equipped mic. belonging to the norwegian broadcasting company.

DI Box

This is mentioned near the beginning of the article, with no explanation as to what it is. I have a rough idea, but not really enough to add it to the article. Perhaps someone who knows more about this subject could do so? 82.32.46.112 22:06, 21 November 2005 (UTC)

DI box — Omegatron 20:51, 8 December 2006 (UTC)

"Dangers" of phantom power not true

The section on the danger of phantom power is untrue - the maximum current of 14mA is nowhere near enough to cause injury or death.

Shocks and electrocution from microphones are instead from faulty grounding and AC power wiring - the referenced story about a pastor being electrocuted involved faulty wiring on a water heater connected to the baptismal pool. —The preceding unsigned comment was added by 12.161.159.124 (talk) 02:43, 20 January 2007 (UTC).

agreed, the only mentions of phantom power i could find in the reference were saying that it probablly wasn't the cause! signal ground tied to a broken mains ground that rose up because of a fault is a far mroe likely explanation for a shock from a microphone.

I agree also. I'm going to delete those two sentences. SnottyWong talk 15:35, 20 April 2010 (UTC)

I also changed the name of that section from "Dangers" to "Implementation variations", because the section has little to do with the dangers of phantom power (mostly because there are none). If anyone can come up with a better section heading, feel free to replace mine. SnottyWong talk 15:46, 20 April 2010 (UTC)

It may not cause injury (at least not unless you were to intentionally touch it for a reeeeally long time - I heard that if you were to touch both terminals of, say, a 12 V battery for - don't know - a really long time - you'd eventuelly die, as even low current will always shift a few ions through cell membranes of nervous cells and once enough ions are shifted, they'll fire - the DC always shifts them into the same direction - sounds a bit like an urban myth - I'd not be willing to try it out though) but I'm sure it can feel uncomfortable. Also 14 mA across a 10 kOhm resistor (skin resistance in a human will normally be even higher!) would already cause a 140 V to appear across that resistor. So it'll almost always be the voltage that limits current flow in this scenerio, not the current limitation. 79.245.163.217 (talk) 09:21, 12 August 2014 (UTC)

Using wrong cables at the wrong moment may result in a peak current of 10 A ! ( 48 V 5 Ohm , 50 Ohm will still give 1 A ). This may destroy or at least degrade semiconductors at the amp-input or damage the ribbon or magnetise the transformer of a ribbon mic (Intermodulation Distortion). Serial resistors to the capacitors will decrease the current but will heavily degrade noise performance.

--AK45500 (talk) 16:12, 11 July 2017 (UTC)

A phantom power supply is neither a constant voltage source nor a constant current source. The standard requires a resistance of several kOhms in series with the internal voltage source. 48 Volts is the "open circuit" (unloaded) voltage for P48--but the more current a microphone draws, the lower the actual voltage will be at the XLR sockets of the preamp/mixer/recorder. For example, a P48 microphone that draws 4 mA (typical for modern, transformerless condenser mikes) will "see" only ~34 Volts because of the mandated series resistance in the supply.

It's very different from holding on to both terminals of a battery, which has much lower output impedance and can supply much more current. You simply could never get 14 mA from a standard 48-Volt phantom power supply across an external 10 kOhm resistance (skin or whatever); you'd get a fraction of that. And there would be no 140 Volts for sure.

Still, if for any reason the output of a mixer or recorder (i.e. equipment that's not designed to be phantom powered itself) is connected to the phantom-powered input of a mixer, recorder, or mike preamp, the phantom powering on that input should be turned off or otherwise blocked. The phantom supply voltage, even at minuscule current, can cause breakdowns in unprotected output circuitry. It's not a common situation in professional audio, but can happen as the result of last-minute improvising. DSatz (talk) 00:29, 10 March 2019 (UTC)

Not just microphones ...

... see Power over Ethernet--195.137.93.171 (talk) 12:35, 24 November 2010 (UTC)

But that isn't called "phantom power," mostly because the technique is very different. Phantom power is carried on the same conductors that are used for the audio signal, hence no extra conductors or connector pins are needed - hence "phantom." PoE is carried on those extra pairs of the Ethernet cable that aren't used for data. There's nothing "phantom" about it. Jeh (talk) 05:34, 9 March 2013 (UTC)

It's called "phantom" because a dynamic microphone (or differential amplifier) will not see it. The microphone capsule will operate between the "Hot" and "Cold" wires of a balanced signal line, while the phantom power keeps both signal wires of the balanced signalling at +48 V (or whatever voltage is used) in reference to the signal ground. Also, on the input side, a differential amplifier will measure the voltage between "Hot" and "Cold" lines and the +48 V (or whatever) on both will cancel out due to common mode rejection. The voltage between "Hot" and "Cold" is always the signal voltage only - not superimposed on a DC offset - hence "phantom". 79.245.163.217 (talk) 09:33, 12 August 2014 (UTC)

Phantom power is also applicable to active antennas in RF reception. For example, many cars now use active antennas (if you've ever seen a shark fin on a late model car, that's why), and some of them use phantom power. In these applications, you generally use chassis as a ground point, and inject DC voltage on the center conductor of an RF cable, the main goal being cost reduction (one less cable to run). But overall, this page is a very narrow view of a very general concept: any time you want to put power and signal on the same cable -- separating them at either end with appropriate blocks and chokes -- you can call it "phantom power". -- SickOfNewSNs (talk) 21:00, 4 February 2016 (UTC)

Cross post from XLR connector

Please Talk:XLR connector#Parallel powering information for questions about early phantom power scheme and discussion of article overlap. --Kvng (talk) 23:12, 17 March 2011 (UTC)

Phantom power damage

There's been an assertion made in XLR_connector#Phantom_power that phantom power can damage microphones that don't require it. Generally this is not true but apparently there are some vintage ribbon microphones that are vulnerable. And it is much easier for phantom power to fry something if you're using a miswired cable. Here are some marginal references I found on the issue - [1], [2], [3] and [4]. I think we should add some mention of this issue to this article. I have removed the uncited claims from XLR_connector#Phantom_power and directed discussion here. The claim in some of the refs is that it is best practice to disable phantom power where not needed. Does anyone have a more reliable source to back this up? -—Kvng 02:51, 9 March 2013 (UTC)

I have added some cases that demonstrate the problem. (a) miswired cable (b) unbalanced microphone and (c) long cables where pin 2 or 3 contact significantly sooner than the other one. Current flows into the capacitance of the cable which can produce enough of a transient across a ribbon to destroy it.Altaphon (talk) 23:16, 4 June 2015 (UTC)

The Royer people would certainly know whether their mics could be damaged by phantom. The Media College website guide is not so unreliable. At any rate, here are some standard textbooks discussing the issue:

• Tomlinson Holman: Sound for Film and Television, page 304, "...it is generally not good practice to supply unpowered microphones with [phantom] power. What may happen is a connection accident in which one side of the balanced line becomes connected first, applying the DC voltage to a microphone not designed to handle it. Phantom power is thus often switchable, even on a per-channel basis..."
• Gary Davis, Ralph Jones: The Sound Reinforcement Handbook, page 130, "A dynamic mic connected unbalanced to a phantom power input may be destroyed, however! It is therefore very important to be aware of whether a mixing console input is wired for phantom power. Most such inputs provide a switch to disable the phantom power when it is not needed. Always be sure that this switch is set to off when dynamics, or electret condensers with internal batteries, are connected to the input."

Holman, Davis and Jones are very much respected in the pro sound field. These sources are top notch. Binksternet (talk) 05:09, 9 March 2013 (UTC)

Great references for the claim of fact about possible damage. Some will argue that the advice to disable it doesn't belong in the article at all - see WP:NOTHOWTO. I believe it is defensible though to quote that advice from one of the references, or otherwise directly citing the references. It just shouldn't appear to be something a WP editor thought up. Jeh (talk) 05:34, 9 March 2013 (UTC)

Also, moving the phantom power details out of the XLR article was a good idea. Jeh (talk) 06:11, 9 March 2013 (UTC)

We do not have to present the information in the form of advice, we can instead describe how and when phantom power might damage a microphone. Binksternet (talk) 15:51, 9 March 2013 (UTC)

Here's a detailed and credible treatment of the topic. Also note some credible followup. -—Kvng 18:04, 25 April 2013 (UTC)

 Done I've added a few sentences and a bunch of refs to the Caveat section. ~KvnG 14:48, 5 June 2013 (UTC)

and some more from me including the cable capacitance case which surprised me when I saw a toasted 44BX from this cause. Altaphon (talk) 23:16, 4 June 2015 (UTC)

"Other microphone powering techniques" section

Does this really belong here? The techniques described have very little in common with phantom power. Shouldn't this material be in the "Microphones" article? Jeh (talk) 06:16, 28 April 2013 (UTC)

Since phantom power is a solution for powering microphones, I think that related methods for powering microphones ought to be summarized briefly, to show the problems that phantom powering solves, or to tell the reader how the field has some confusing practices. Binksternet (talk) 15:42, 28 April 2013 (UTC)

But the article isn't called "methods for powering microphones". It's called "Phantom power" and the lede makes specific reference to a standard that does not include these other methods. I'm suggesting moving the details of the "other methods" to the "Microphones" article and leaving a reference to that article here, with brief descriptions - say one sentence for each method. Jeh (talk) 20:26, 28 April 2013 (UTC)

I think the information is better placed here than in Microphone. You can propose a change of title or clarify the lead to indicate that the scope of this article extends beyond IEC 61938. -—Kvng 18:28, 1 May 2013 (UTC)

OTHER uses

   Active antennas
   Low-noise block downconverter
   Power over Ethernet

This are 3 NOT phantom powered devices. I will delete these wrong information. Phantom power requires symetric lines and a seperate ground.

--AK45500 (talk) 15:48, 11 July 2017 (UTC)

Bias tees

Perhaps Bias tees should be linked somewhere. Hhm8 (talk) 03:20, 3 December 2015 (UTC)

Etymology of "Phantom Power", or "why not just Power?"

I find that the page is missing details as to why it's called "Phantom Power", because if one thinks hard enough there is always obviously a power supply if you go far enough back in the circuit. Various comments on internet blogs suggest that the simplest and most obvious reason is because early condenser microphones used to have an auxiliary power cable, which is no longer present, thus "phantom" power--when it is actually being delivered on the same cable the audio signal travels through. Though this explanation were true, then it would imply that the terminology is somewhat deprecated since it is quickly escaping living memory. — Preceding unsigned comment added by 47.157.137.55 (talk • contribs)

Douglas Spotted Eagle wrote in 2005 that phantom power got its name from being "a power source that you can't really see."[5] I would challenge his definition by pointing out that it's possible to buy a very visible external power source[6] which is called a phantom power unit.

The Mackie mixer instruction book from the 1990s says "It's called phantom power because the voltage supplied to the mics travels on the mic cable itself, without any extra wires."[7]

John Eiche wrote the following in 1990 on page 55 of Guide to Sound Systems for Worship: "Sometimes provision is made to supply this voltage directly through the microphone cable. This procedure is called phantom powering."

I was taught in the late 1980s that the name refers to a power source on the XLR line that dynamic mics ignore. They can't see it but it's there, so it's 'phantom' in that sense. Binksternet (talk) 04:40, 28 June 2020 (UTC)

The name "phantom power" derives from the Phantom circuit, which was known and used already since the 19th century in telegraphy/telephony. The Power-over-Ethernet circuit is almost directly taken from this old circuit, therefore PoE is correctly referred to as an application of phantom power. The microphone powering scheme is essentially one half of it. The distinguishing feature is the use of a balanced pair as one leg of the phantom circuit, while the other leg can be a ground connection or another balanced pair. The separation between the main circuit and the phantom circuit hinges on the balance of the main circuit. This is in contrast to circuits that impress a DC voltage onto the main circuit, where the separation is done in the frequency domain, with a diplexer or bias tee. 2A03:80:B3F:F500:68CF:EF25:40EA:911B (talk) 08:51, 30 April 2023 (UTC)

Schematic error

I note that in section 'Standards', Altaphon says "The schematic drawing is wrong, I will provide a corrected one soon", but this was 12 years ago (21:01, 7 March 2011 (UTC)), and the schematic [[8]] (may have been changed, but) is still wrong, and its caption misleading:

Assuming that the label "In" implies "From microphone", with C1-C2 in the positions shown, the microphone is not protected from the full 48v supply, while R3-R6 & D1-D4 are redundant (at best); while if the microphone goes on the other end, C1-C2 will prevent any DC power from reaching it. Wasn't anyone else paying attention?

I shan't attempt to supply a correction: I'm new here, I read schematics not design them, I don't have a verified alternative, and I have no experience of editing/creating schematics in .png. (Do I get an automatic timestamp? In case not) 21 June 2023 — Preceding unsigned comment added by Hal at Springmire (talk • contribs) 22:11, 21 June 2023 (UTC)

The basic circuit is 48 v to pin 2 and 3 through individual 6.8 k resistors (R1 and R2). This circuit has extra elements to protect the preamp from transients that can be generated with the mic is plugged or unplugged.

Altaphon's concern was There should never be an R3, this is commonly done by some makers to eat some power supply hum but there is no substitute for a clean, low impedance +48 feed. The purpose of R3 and R4 is as a current limit for the diodes during transient supression. These 10 ohm resistors should have no effect on normal microphone signals and don't have anything to do with hum.

Hal at Springmire, the microphone needs to receive the 48 v, not be protected from it. If a non-phantom mic is connected, it receives the same 48 v on both pin 2 and 3 so no phantom power current should flow through it. ~Kvng (talk) 11:54, 25 June 2023 (UTC)