We have all heard stories about how providing 48v phantom power to microphones that do not require it can cause damage to the mic. But if that is the case, why do some interface and console manufacturers only provide global or sectional phantom power switching? In this article, we are going to do our best to get to the bottom of the myths surrounding 48v phantom power with the help of some seriously qualified friends.

Our Panel

Trever Coley is the Founder and Designer of Sontronics Microphones. For nearly 15 years this small British manufacturer has been producing mics that punch well above their weight when it comes to sonic performance. It’s no secret that James Ivey is a big fan of Sontronics mics for drums, guitars and vocals.

Robin Porter is the Chief Designer at AMS Neve. He is responsible for the Neve 88RS, BCM-10 MK2 and Genesis Black consoles along with plenty of other phenomenal sounding audio equipment which wears the Neve badge. When it comes to console design there are few more qualified in the world to talk about circuit design and console layout.

Sean Karpowicz is the founder and Managing Director of new company Cranbourne Audio. Sean has been a recording and live sound engineer for more than 15 years. His experience with music and audio evolved and led him to design audio products for leading audio manufacturers. To date, Sean has designed several award-winning audio products including mixing consoles, recording interfaces, microphones, and more.

Derek Bargaehr is the CEO of Vanguard Audio Labs based in California. Derek began burning himself with a soldering iron and messing up his guitar pedals at the age of 15, eventually working as Director of Operations for a successful microphone company for several years. He met the co-founder Ken Avant and started designing and producing microphones under the Vanguard name.

Rick Perrotta is the President of Royer Labs. When most people think ribbon mics they think Royer. Since 1989 when the company was founded Royer have been at the forefront of ribbon mic design and manufacturing. We could not do an article on ribbon mics and phantom power without input from Royer. It would just not be right.

What Is Phantom Power?

Phantom power is a means of providing power to microphones (most commonly condenser mics) that need power for internal electronics without the need for a separate and costly power supply unit. The main bonus of Phantom Power is that it travels along the same cable as the mic uses to get its signal into the mixing console or audio interface. Think of it this way, the mic’s output travels from the mic to the interface or console whereas the Phantom Power travels from the interface or desk to the mic.

Myth 1 - Global Phantom Power Is Bad

By Global Phantom Power we mean where an audio interface or mixing desk has a single switch to turn Phantom Power on for all channels at the same time. There is a myth that this is not a good idea as it means the same power supply feeds all the channels at the same time, therefore, the quality of the phantom power can not be as good.

Robin Porter

Phantom power was slowly introduced onto Neve consoles as the need to power new mics that came onto the market, which did not have their own power supplies. Up to then, most condenser mics came with their own power supplies. Splitting the PSU away from the mic allowed mic manufactures to make condenser mics cheaper to customers.

Early Neve consoles had +48v present on the mic inputs all the time. It was done this way as most mics had transformer outputs so did not need protecting with a switch. Adding a switch had a cost to it and took up desk real estate.

It was not until the mid-1980s that a switch for phantom power started to appear on all Neve consoles the first being the Neve V1.

Trevor Coley

It is generally safe to connect the vast majority of non-phantom powered dynamic and ribbon microphones to a system that has permanent 48V. These mics should be balanced and the voltage will have no effect on the microphone or its output.

Derek Bargaehr

Balanced mics, including most if not all modern ribbons, should have no problem if phantom is turned on while it is plugged in. Transformers block DC (and phantom power is DC). The ribbon is behind the transformer, which is shielding it from DC.

Myth 2 - Ribbons Mics Can Be Damaged By Phantom Power

I’m sure we have all heard the story of the engineer who plugged an expensive ribbon mic into a console not realising that the phantom power was switched on and fried the mic. We asked our panel if this was at all possible and if today’s modern ribbon microphones can be damaged by phantom power.

Trevor Coley

It's worth pointing out that some old ribbon mics have their output transformers connected to ground, and therefore this means that current would pass through them and potentially cause damage. Therefore, DO NOT connect your vintage ribbon mic to a desk/preamp/interface unless you are 100% certain that there is no 48v present!

99% of modern Ribbon mics will have a transformer in their output stage so having phantom power switched on will not affect them in any way. I should point out that good quality cables have pin 1 connected to the chassis of the connector and therefore, to earth, which deals with any errant and unwanted 48v so the importance of properly wired cables should not be overestimated.

Robin Porter

In regards to blowing up Ribbon mics with phantom power, this is very rare as most ribbon mics have output transformers and are balanced. I think most of the problems with ribbons are incorrectly wired cables and ad-hoc repair/modding of mics. You are less likely to blow up ribbons these days as the feed resistors are a higher value than before (1970’s). Early phantom power feed resistors would be in the order of 1K-3K ohms resistance but are now standardised to 6.8K ohms. This makes the current less, so its less likely to cause problems, Also using 6.8K ohms does not affect the input impedance. 6.8K ohms was chosen as a compromise between the current needed to be supplied for the various microphones, typically in the range of 3 milliamps to 10 milliamps.

Sean Karpowicz

Old ribbons and old dynamics can be problematic. Newer mics are fine thanks to new output circuit designs and components which can deal with phantom power on or off. The big issue is when connecting a line signal when the 48V phantom power is on. There are 3 possible scenarios:

• Transformer on the output, therefore, the line output is isolated. All fine!

• Floating output - This will bring the voltage up and potentially fry components. If this does not kill the line output you might have some added distortion to the signal.

• Non-floating output - This will cause a DC (Direct Current) offset which may cause loud thumps any time you switch something. Components could also get fried and kill the output circuit.

One catastrophic thing is to have 48V on with the capacitor charged and then hot-plug the cable OUT of the mic or the interface/console/desk. This will 9 times out of 10 fry output resistors and maybe op-amps in the output circuit. Obviously this is to be avoided.

Rick Perrotta

The issue with some “vintage” ribbon mics being damaged by phantom power is not a myth at all, and the issue centres around how the microphone was internally wired by design. Some old school mics connected the ground (pin 1) to a centre-tapped transformer to keep noise and hum to a minimum, these are most vulnerable. However, modern microphones can also be damaged under certain conditions. It is not the absence or presence of phantom that is the threat here but how it is applied. The output of a mic is a balanced signal provided to pins 2 & 3 normally, through a specially designed impedance matching transformer. Any voltage imposed between these two pins is directly transferred through the transformer and imposed across the ribbon. If the voltage is ample, the ribbon can deflect, deform, or blow like a fuse depending on the voltage and current. Under normal circumstances, the phantom voltage is applied evenly across pins 2 & 3 and nothing happens. If a voltage is applied in an unsafe manner, such as a faulty cable or cross-patching at a patch bay, a substantial voltage can momentarily be placed across pins 2 & 3 in an unsafe manner.

Even with switchable console phantom a problem can arise or with certain outboard preamps such as a Daking that has phantom on all the time. If that preamp is configured through a patch-bay and a mic is cross patched even with console phantom OFF a voltage can be passed on dangerously to the microphone.

Derek Bargaehr

The problem starts when a ribbon mic is plugged/unplugged while phantom is on or worse you are using a patch bay to patch a ribbon mic while phantom is on. Switching phantom on and off WHILE the ribbon is plugged in, should not cause an issue, as the voltage will hit pins 2/3 in the XLR socket of the mic at the same time.

Plugging/unplugging is only an issue because you're technically pulsing an initial DC transient across the transformer as you plug/unplug, which could stretch or tear the ribbon if it's a high enough transient (in this case, treat the DC spike like an AC signal that is going to throw the ribbon to one extreme or another.) In theory, hot-swapping a ribbon with good XLR cables/connectors should not cause this issue as pin 1 (ground) connects 1st on most XLR cables. The exception is a damaged cable where there's a short between pin 2 or 3 and ground or a worn-out connector that isn't making great contact. With a good phantom power supply, on the other hand, there will be a slow ramp-up to the 48V, as opposed to a sudden 48V surge (i.e., the transient). This is all to say - hot-swapping can be fine, but is not ideal.

However, the most problematic issue is using a patch bay, which temporarily shorts phantom to ground during plugging/unplugging if the patch bay has phantom running through it. This can turn a ribbon into very expensive aluminium confetti and should be avoided.

The exception to all of this being centre-tapped output transformers where the centre connection goes to ground. IIRC, RCA did this with certain models, but not all of them. This was before phantom power was even a feature on consoles and I don't know of any modern ribbons that do this today. A centre tapped output transformer and phantom power do not get on.

Ribbon Mic And Phantom Power Best Practice

As I am hoping you have gleaned from the information in this article there are no real “rules” to the phantom power and microphones issue, but there are what we might call some codes of best practice that we should all stick too and by doing so we can make sure that all our gear stays in a safe working condition for years to come.

1. Always use a properly configured XLR cable. This means that pin 1 should be the ground or earth cable with a tag from this pin going to the case of the XLR plug. Pin 2 is positive and pin 3 is the negative connection. If there is any doubt about this dig out a multi-meter and check it.

2. Where possible turn phantom power off when you are not using it. This has nothing to do with mics but any device that has any featured turned on let alone phantom power that you are not using is probably using more electricity. So do your little bit for planet Earth and also your pocket.

3. If phantom power has to be on, make sure all the mics that are being connected to the interface/mixer are fine with receiving phantom power. If there is any doubt then leave them out of your rig. As our expert panel have explained, 99% of modern dynamic, condenser and ribbon mics (probably all of those in most of our collections) will be absolutely fine receiving 48v but if you do have a stash of vintage ribbons the safest thing to do is to not connect these with phantom power on without doing some checking. That said, the chances are that is you have a collection of old vintage ribbon mics, then you probably know quite a bit about them and you know what they can and can’t take.

4. If you are connecting mics through a patch bay make sure the phantom power is switched off before you make any connections. While an XLR plugs pins should all make the connection in the correct order or at the same time the same can not be said for a TRS jack sliding into a patch bay. Best practice implies that you should not bring phantom-powered signals up to a patch bay but it does happen so just be aware if you are routing signals via a patch bay, even one using GPO or Bantam jacks switch the 48v phantom power off when patching.

Robin Porter

With regards to safety and best practice, always make sure your mic is fully balanced and can take +48v without trouble. Always make sure the cables you are using are wired correctly. Never hotplug mics (even condensers) take your time swapping over and you will not have any problems.

Derek Bargaehr

Some tips for best practice.

• Use high-quality XLR cables that are regularly checked with a cable tester for ground shorts.

• If possible, only plug/unplug all mics when global phantom power is off.

• Always mute your outputs/channels to avoid speaker-damaging pops when plugging/unplugging mics with phantom power on or turning phantom on/off.

• If you have to use a ribbon with global phantom power, best practice is to make sure it's plugged in before turning phantom on.

• Don't use a patch bay when using global phantom power, or make certain that phantom is deactivated when patching. Shorting 48V to ground is not a good idea for any mic In theory, you could also damage a condenser mic this way.

Rick Perrotta

The best rule of thumb is with a passive ribbon mic, make sure your cables and connectors are in good nick and keep Phantom off. Then obviously, with phantom-powered ribbon mics, the phantom power is required or the mic simply won’t work at all, other than some possible bleed-through.

Production Expert would like to thank Robin, Trevor, Derek, Rick and Sean for their contributions to this article. If you have any related questions please do add them to the comments section and we will do our very best to get them answered.

If you know of any other studio myths that you feel could do with some light being shed on them also please let us know about them in the comments section.