Microphone connections

I have written a lot of on electret microphone connections on my Powering microphones document. Here are some additions to my documents on electret microphones I found at SANKEN Basis of Wiring Method web page.

The first circuit diagram shows the traditional “2 wire” method of wiring an electret capsule. Practically all electrets I have worked with have been wired using this same idea (2 wire capsules have the FET is included in the microphone head wired in this way).

2wirebasis_e
Image source: http://www.sanken-mic.com/en/qanda/index.cfm

This method can have approx.10dB gain because of FET DRAIN output which is usually good thing. The downside is that this kind of microphones can have have some unevenness in output level because of FET gm difference. Also the mic may have a negative phase output signal when it has a positive sound wave. Usually those are not a bog deal.

Here is another way to wire a 3-wire electret capsule with somewhat different properties:

3wirebasis_e
Image source: http://www.sanken-mic.com/en/qanda/index.cfm

In this circuit there is no gain because a signal is FET SOURCE output (so the output signal level is around 10 dB lower). And I expect to get a positive phase output signal from positive sound wave.

Third thing I have sometimes wondered is the wiring of the mini XLR connectors used on some wireless microphone transmitters. The hCOS-11D PT Wiring Method for AKG Transmitter page gives one idea of such wiring. The page has also links to wiring instructions for many other transmitters.

37 Comments

  1. Andres Paparelli says:

    How did you wire up that beast? Looks like a lot of work on that single phase motor.

    Reply
  2. Hiedi Pitzen says:

    Im grateful for the article.Thanks Again. Really Great.

    Reply
  3. Reta Sego says:

    Enjoyed every bit of your blog.Much thanks again. Awesome.

    Reply
  4. Quyen Mesa says:

    i bought a Soundboard and a Mic. Another 1 in the operates– have been truly hectic. Really Occupied. As in: no time to fuck away

    Reply
  5. Nuri says:

    Tanks for all mic infos. (preamp vs)
    Nice and usefull blog.

    Reply
  6. GF says:

    Hi all,
    I have a strange problem with my radio audio device.
    If I connect to mic in a cd player in the headset in the other room I have a good quality for audio stream but if i connect a microphone (pc microphone) the audio stream is very low quality.

    Can help me?
    I tried your scheme but the result is the same.
    Bye

    Reply
    • tomi says:

      I need more details to be able to give good advice.

      Can you give more details on the exact devices used on your setup?
      And also what kind of quality problems do you have in your audio stream?

      Reply
  7. Martin Howard says:

    How can I connect my Electret headset with it’s 3.5mm plug (sennheiser ME 3) normally used with my computer through a buddy 6g usb interface, with my Mackie mixer that accepts XLR input?

    Reply
  8. Raylene Delgardo says:

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    Reply
  9. CSS says:

    Quick question:

    In trying to source some cheap lavalier microphones, I’m finding a ton on Ebay that were originally sold as part of a wireless transmitter. Some have a 4 pin “mini” xlr, some have a 3.5mm headphone plug. I’m having a heck of a time finding just how these are powered – is it real phantom power, or bias current? No specs, and the only official solution is to buy a $80-$150 inline mystery device that has a standard xlr plug on one end and the a jack to match the lav mic on the other (and of course, takes batteries).

    Have you come across any of these and attempted to power them without their matching transmitter pack?

    Reply
    • tomi says:

      All cheap lavalier microphones riginally sold as part of a wireless transmitter I know are based on small electret microphone capsules.
      The ones that have a 3.5mm headphone plug are powered with bias current. More details on powering practices can be found at
      http://www.epanorama.net/circuits/microphone_powering.html

      With mini XLR connections I don’t have that much experience in building custom cables for those.
      I quess the wiring practices could vary from manufacturer to manufacturer. Most probably you can sort out details
      by opening the mini-XLR connector and see which wires go where… I expect that one pin is ground, other is signal
      and then there is a pin for mic power
      (either bias current that can be directly wired to mic or battery voltage that is fed though resistor to mic).

      Google search gave some details on some mini XLR wirings on those documents
      http://www.altronics.com.au/download/Data/Data10.PDF
      http://taperssection.com/index.php?topic=139770.0

      Reply
  10. materace gimnastyczne says:

    I enjoy reading an article that will make men and women think.
    Also, thanks for allowing for me to comment!

    Reply
  11. tveod says:

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    Reply
  12. David Balcaen says:

    Hi,
    I have a sony ecm-ds70p 3.5mm stereo electret microphone that I want to purchase an adapter for to feed either two 1/4″ plugs, or XLR. The mixer is a really small two channel Apogee duet, and does include 48 volt phantom powering on the XLR balanced input. Do you know of any adapter that will do either conversion (and powering) of the electret for me, or am I on my own and will have to build a simple power, and audio pass through device myself? From your great articles the method is clear to me, just wondering if there is a device already assembled to do this. A long shot request.

    Reply
    • tomi says:

      There are ready made products available.
      I have seen them on some fairs and catalogues for different electret microphones.
      Where they could find exactly suitable for your case I can’t help.
      In some case you might find something exactly right, and some other cases you can use something you can get with some adaptation (like special DIY cable).

      Reply
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    • tomi says:

      Thank you for your feedback.
      Actually I already use the akismet plugin from wordpress.
      It is a great product. It has stopped a huge amount of spam comments.
      Unfortunately it does not seem to be able to catch all spam (I think it catches 99% or so), so still some of it still gets though.

      Reply
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  18. Peter Kobl says:

    Hi,
    you write a good blog here. The information is detailed and based on your testing and experience. I’ve used your blogs, also the other ones, from time to time over a couple of years and always found them highly informative and better than the rest.

    I’m doing a project where a microcontroller is used to interface to PC sound cards, e.g. High Definition Audio cards that seem to be the standard now in newish PCs and laptops. The microcontroller composes synthetic sound waves and “writes” them to the PC microphone (3.5 mm input jack). After a couple of attemps by trial and error and google I ended up with an interface circuit like this:

    MCU
    |

    Reply
  19. Peter Kobl says:

    ups seems to submit blog comments.

    I’ll try again

    MCU is powered separately. But indirectly from the USB on the same PC. (And I suppose the sound card is internally of the USB type)

    MCU pin (digital not analog, max 3.5v)
    |
    |
    100k
    |
    _________________ to Microphone signal (left and right channel)
    |
    10k
    |
    __________________ Microphone ground (common with MCU ground)

    seems to work OK. Nice clean signal that oscillates around 0.3v +- 0,10v. When connected to the microphone jack that goes up to 3-4 volts but I suppose that is phantom power.

    I’m a little worried though that it might stress the PC microphone pre-amplifier. Do you think a capacitor in series with the signal would be advisable, or anything else? I would appreciate your comments.

    regards,
    Peter Kobl

    Reply
  20. JM Sound Hire says:

    Hello,
    This blog is all about music and wireless microphone.Now a days,it has a very high demand.
    JM Sound Hire

    Reply
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  22. Lehel says:

    Dear Mr,

    I need to connect an unbalanced signal to a balanced and phantom powered microphone input, and no possibility to stop the phantom power (i want to connect my walkie talkie output to the Talkback input of a Behringer X32 mixer). is there any possibility to make the connection with capacitor or a resistor?

    Reply
    • Tomi Engdahl says:

      You can block phantom power with similar circuit as phanotm power is fed. Foe example circuit in figure 2 at
      http://sound.westhost.com/project96.htm

      Instead of feeding 48V to the circuit you connect nothing to this +48V input.
      You might be able to leave out R1, R2 and C9.

      A 1:1 transformer is another option for phantom power blocking (will also do nice unbalanced to balanced conversion).
      If you have suitable audio transformer available that would be a good option to consider – the transformer does not have to
      be any high quality for walkie-talkie limited audio quality, a cheap “telephone transformer” would do acceptably here.
      Same idea as in DI boxes like http://whirlwindusa.com/media/uploads/dischem_600w.jpg

      Reply
  23. Lehel says:

    Ok, thank you very much!

    Reply
  24. Lehel says:

    Based on Figure2, which part should i connect to the phantom powered input? The left side/ XLR side?
    In order to get an unbalanced input, should I short the ,,Mic – ” with the ground?

    Reply
  25. Dennis says:

    Dear Mr Engdahl.
    Wow! This is all you need around building an electret microphone!
    I asked myself which circuit I should go for building a battery powered mic (maybe an AAA or 9V) that can be connected to an acoustic amplifier. For example to amplify a steelstring/concert guitar. Those amps have a high impedance 1/4 jack input.
    I’d be very thankful for a short answer.
    Kind regards and thanks for your time!
    Dennis from Germany

    Reply
    • Tomi Engdahl says:

      I quess that the the signal from elecret microphone powering circuit could work with guitar amplfier quite well (but I have not tested because I don’t have guitar amplifier).

      According to page http://www.diystompboxes.com/smfforum/index.php?topic=81285.0 the signal level you get from electret mic should be in right right range for typical guitar amplifier (and impedance should no be problem).

      “Various pickups, players, styles, etc, peak 200mV to over 1V. Most of the classic inputs will overload at 1V-2V, and this has been acceptable.
      You want enough gain to bring 20mV up to maximum clean power. This allows soft fingering to come out loud, and allows overdrive when desired.
      Some mega-fuzz amps have input sensitivity below 1mV.”

      “Since guitar pickup level apparently never exceeds 1.5V peak (or it is acceptable to clip at 1.5V), 3V peak-peak”

      Page https://en.wikipedia.org/wiki/Pickup_(music_technology) says:

      The output voltage of magnetic pickups varies between 100 mV rms to over 1 V rms for some of the higher output types.

      From http://www.soundonsound.com/sound-advice/q-can-re-amp-line-level-signal :
      “Guitar amps are designed to accept a high-impedance input, and plugging in a low-impedance, line-level signal will result in an increase in amp hiss. This will be more of problem if you like to turn your amp up loud. There are a number of possible solutions.”

      Reply

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