Electret microphone phantom powering idea

This article can be seen as continuation to my Powering microphones document and  PC microphone phantom powering improvements blog posting.

Jon Blackstone said in comment:

Tom -

I’ve got a solution for this that’s very simple, and is working for me.

I connect the ECM capsule (cheesy computer mic) directly to pins 2 and 3, and just pull pin 3 towards ground (pin 1) with a 47K resistor to create a 6V differential across the ECM.

(both mic wires insulated from any metal casing

This avoids attenuating the signal as the 3-resistor scheme does. And I may be mistaken, but I think it’s even roughly “impedance balanced”, as the ECM floats much the way a transformer in a dynamic mic would (the 47K additional loading on one side being negligible).

Am I missing something?

And my comments to that was:
That stripping down of spaces is a feature of this blog system commenting.

I still understood the drawing anyway.

And I think that your idea is a really good idea indeed.
I have to test it.

I tested the circuit and got it working… So the idea works in practice. Here is prototype I used for testing:

This circuit can be viewed as kind of modification of this circuit from Powering microphones document:

   HOT (2) ---------|_____|------+
                    47 kohm      |+
  COLD (3) ----+              CAPSULE
               |                 |-
GROUND (1) ----+-----------------+

But the suggested new circuit (fshown below) improves this design by getting rid of signal attenuation caused by 47 kohm resistor and the signal from mic is fed to XLR input in balanced format.

(both mic wires insulated from any metal casing

There is still ther downside is that this circuit loads the phantom power in very unbalanced way which can disturb some older mixers. Other downside of this simple design is very high output impedance (logn cables atenuate signal high frequencies very much). Also one doenside od this new design is that both sides of elecret capsule are at quite high potential (easily over +40V DC with 48V phantom power). So this does not suit for PC microphones that expect to be grounded. But for discrete small electret capsules this works – make sure that mic case does not make accidental contact to anything (ground or people, 40V can cause some electrical shock that can be nasty). You have been warned.

I think thait improvemrnt idea somehow imperives the original deisgn, but it is not optimized and right in any way, but coudl be good enough in many cases. If you want to read how to do the adaptation correctly my Powering microphones document docment and Electret Microphones – Powering & Uses web page for details.



More material:






Phantom power adapter circuits:




  1. Tomi Engdahl says:

    Neewer model NW-700 “Professional Studio Broadcasting & Recording Condenser Microphone,”

  2. Tomi Engdahl says:


    Phantom power is required for recording with any condenser microphone. Most audio interfaces and mixers have phantom power built-in for this purpose. However, dynamic microphones and other equipment don’t need it to function.

    In some cases, phantom power can damage equipment. Although dynamic microphones are unlikely to be damaged, sending phantom power to a ribbon microphone can cause permanent damage. It is also advised to turn phantom power off before connecting other equipment like line-in instruments and monitors.

    . Condenser microphones are the only form of equipment that requires phantom power to function. Without it, the microphone simply won’t turn on, and it will be rendered useless when it comes to capturing audio.

    There are some exceptions to this rule, but, rarely, a condenser mic will not need phantom power.

    In most cases, if you accidentally leave phantom power on while using a dynamic microphone, it won’t cause it any harm. In live sound situations, the phantom power being present will likely be unnoticeable.

    If, however, you are using a dynamic microphone to record, phantom power tends to plague the recordings with an electronic hum. This is caused by the surge of phantom power which is unnecessary for the dynamic microphone to operate.

    The only likely situation where phantom power can damage a dynamic mic is when there is a problem with the XLR cable used to connect it to an interface or other piece of recording equipment.

    Ribbon Mics & Phantom Power (How To Avoid Damage)

    Ribbon microphones are commonly used to record loud sound sources, like drums.

    This vintage-style recording equipment comes in two forms: those that require phantom power, and those that will be damaged by it. The latter is the most common type of ribbon microphone, so if you are using one you should always refer to the individual specs to protect it from harm.

    Leaving phantom power on when using a ribbon mic can result in the internal ribbons being stretched, or in some cases, completely blown. The presence of the additional power is too much for the ribbons to cope with, and the result is often permanent damage that cannot be repaired, or significantly impacts the ability of the mic.

    Line-In Instruments & Phantom Power

    Another form of equipment that can be damaged by phantom power is line-in instruments. Sometimes called line-level gear, this category includes any keyboards, guitar, or other electrical instruments that don’t require external power to be recorded.

    Line level gear includes:

    Electric Guitars & Basses
    Other electronic string instruments
    Outboard effects

    If line-level devices are used with phantom power turned on, this can result in the output electronics being fried.

    This is why most audio interfaces and mixers are equipped with specific line-level inputs, which is where instruments should be connected. Plugging a line-in device into an XLR mic input is not advised, especially when phantom power is being sent to that input.

    Different interfaces distribute phantom power in varying ways.

    Some may send the phantom power to all of the inputs in a single block, while other, more sophisticated devices offer phantom power for each input.

    Again, checking the specs of the equipment you are using is the only way to definitively know the ins and outs of their phantom power operation.

    Likewise, some instruments and line-level devices will be fitted with protective measures to avoid phantom power from causing them damage. Most of this equipment will survive for a short period while phantom power is connected, but after around a minute, the damage is likely to occur.

    The longer you leave a preamp or line-level device plugged into an interface that is producing phantom power, the greater the risk of damage.

    Monitors & Phantom Power Damage

    In some cases, phantom power can also cause damage to unbalanced output devices. If you have ever turned on phantom power while your studio monitors are active, you’ve probably noticed the sharp pop that is sent through the speakers.

    Does phantom power damage headphones?

    It’s very unlikely that phantom power will damage a pair of headphones. Most interfaces have separate headphone outputs which are independent of the channels where the phantom power is present.

  3. Tomi Engdahl says:


    Guitars And Power Requirements

    Neither acoustic nor electric guitars require phantom power. Electric guitars are relatively low impedance devices, which operate at line level. This means they do not require additional voltage to operate.

    Likewise, acoustic guitars are also line-level instruments. The only difference is that acoustic guitars do commonly use a pickup which is combined with a preamp, but this device is powered by a 9-volt battery in the majority of cases.

    Nevertheless, it’s very common to record both electric and acoustic guitars using condenser microphones. So technically, the guitar may be indirectly dependant on the extra voltage, to capture the full scope of its detailed sound.

    When you’re recording guitars or any other instrument for that matter, should you be cautious about accidentally leaving +48v phantom power turned on?

    Although it’s certainly advisable to turn off phantom power when you don’t need it, leaving it on is unlikely to damage your guitar.

    This is because phantom power can only be sent through the second and third pins in a balanced XLR cable.

    Guitars typically use ¼ inch TS cables, which are unbalanced and have a tip-sleeve design rather than the 3-pin design of their XLR equivalents.

    When phantom power is used with a condenser microphone, it activates the capsule within the device, which feeds the inbuilt amplifier. It is exclusive to XLR cables, and cannot be used with TS/TRS jack cables.

    The reason for this is that TS and TRS jack cables which are commonly used for connecting guitars and other live level instruments have contact points that don’t connect simultaneously.

    When you plug a guitar jack cable in, the tip enters the input first, followed by the ring, and then the sleeve. The connection is therefore established one step at a time.

    Conversely, when you plug an XLR cable into a balanced input, each of its three pins connects at the same time.

    Leaving Phantom Power On When Recording Guitar

    In theory, the only way that phantom power could damage your guitar is if you connected it to the interface or mixer using a balanced cable.

    All guitars have a jack output, so this would mean you’d need to use a cable that had a male XLR connector at one end, and a TS or TRS jack connector at the other end.

    There are practically no situations where this would be beneficial, however.

  4. Tomi Engdahl says:


    Phantom power is an important and essential feature of a microphone preamplifier. All Sound Devices mixers and recorders that include microphone preamplifiers offer phantom power, conforming to the IEC specification. Select Sound Devices products also offer phantom power for line-level signals, since many microphones can output very high signal levels in the presence of high-sound-pressure-levels, such as concert and gun recordings.

    Phantom power, however, has the potential to damage equipment not designed for it, specifically devices with unbalanced outputs. Unless the device is designed to accept phantom power, do not apply phantom. Some unbalanced equipment does not have any, or sufficient, protection from DC voltage and its output circuitry can be damaged, requiring repair.
    Important Reminders for using Phantom Power

    If a single-ended (unbalanced) output device such as a keyboard, consumer tape deck, sound card, or receiver is connected to any balanced preamp, make certain phantom power is turned off on that input. Depending on the design of the device, its output can be permanently damaged if phantom is applied.
    When connecting a single-ended (unbalanced) output device to a balanced mic preamp with phantom, use an isolation transformer at the unbalanced device output to be certain that any phantom that may inadvertently be present is isolated.
    If connecting to a product which is suspected of having inadequate output protections and phantom power is not defeatable, use a build-out resistor of roughly 1k ohm in the “hot” leg to help mitigate effects of the phantom voltage.
    Some balanced output devices, such as T-powered microphones and dynamic ribbon microphones, can be permanently damaged if phantom power is applied to them. Turn off phantom when connecting these types of equipment.
    With all Sound Devices mixers and recorders, each input channel has its own phantom power control. Be familiar with it and turn phantom off when connecting devices that can be damaged by phantom power.

  5. Tomi Engdahl says:

    Electric shock from phantom power

    believe that phantom power isgeneraly limited by a 6700ohm resistor on both legs inside the desk, at 48V this gives you just over 7mA if you have been able to short pins 2 and 3 this would be 14mA, just about enough to light an LED. I’m surprised that an artist would complain about recieving a shock at this level. I would check that there are no earth loop issues as well.

    48V is plenty to give a shock especially if it’s handled with sweaty hands. Just ask telephone engineers!!

  6. Tomi Engdahl says:


    What potential electric shock hazard exists when using a phantom powered microphone in an environment where there is a potential for the mic and/or user to be accidentally immersed in water (i.e. an indoor pool facility)? Would it be best to use only dynamic microphones in this application?

    All properly designed phantom power supplies limit the available current to no more 15 milliamps. 48 volts of phantom times 0.015 amps = 0.72 watts. In theory, this small amount of power should not be harmful.

    However, any type of wired mic is connected to an audio mixer and if the mixer is AC powered there always is a possibility of failure within the mixer that might bring the AC hot lead in contact with the chassis and therefore the handle of the microphone – dynamic or condenser.

    The best answer is a wireless microphone which is powered by batteries and has no physical connection to the audio mixer.

  7. Tomi Engdahl says:

    DIY electret microphone adapter to XLR phantom power

  8. Tomi Engdahl says:

    How to make a 3.5 mm stereo to XLR mono adapter cable

  9. Tomi Engdahl says:

    Phantom Powered Telephone to XLR Adapter – The Telephone XLR8OR

    I made an adapter to connect a telephone to a mixer and use it like a microphone. Now I’m showing it to you!

  10. Tomi Engdahl says:

    The Telephone XLR8OR
    A Phantom Powered Analogue Telephone to XLR Adapter

    The Telephone XLR8OR is a small circuit that allows you to connect an old analogue telephone to any mixer or microphone preamp that can supply phantom power and use it for recording

    It works by taking the 48V phantom power present on the two balanced signal lines of the XLR connector (pin 2 and 3) via the resistors R1 and R2 and connecting them across the phone lines using the two 100Ω resistors R3 and R4.
    This causes two out of phase signals to appear at each resistor which can be coupled back into the balanced signal lines via the two capacitors C2 and C3.

    Since the impedance of the phantom power supply is fairly high the power delivered to the phone might not be enough for all telephone functions, but at least for my phone audio and touch tone dialing works fine.


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