Wire a XLR Mic to a Yaesu FT-950

Discussion in 'Radio Circuits, Repair & Performance' started by VK2MTC, Feb 28, 2009.

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  1. VK2MTC

    VK2MTC Ham Member QRZ Page

    Yaesu FT-950 Wiring for a Microphone with a 3 pin XLR Plug to 8 Pin Plug
    & Foot Switch Wiring from REAR PANEL

    The Set Up I was aiming for was for one of Hands Free Operation but not using the Standard Yaesu Microphone/s on offer …. In other words using a Stage/Studio Mic.

    I purchased a RODE Studio Arm so I could have flexibility of movement from the radio to the computer and have the mic in front of me if I wished to do so .

    The Microphone I finished up using – with very good results – was a “REDBACK C0384” Supercardioid Dynamic Microphone with a 300 Ohm Impedance … This microphone has some good features with excellent sensitivity ….

    The XLR plug and the Twin Core Lead that came with the mic is more than adequate for the job but the Wiring inside the Female end (plugs into mic), needs to be modified – they have pins 1 & 3 wired together these NEED to be separated so that there are 3 separate wires from the plug (1, 2 , 3) … The other end of the lead will be cut off so don’t worry about it. (Cut Lead to desired Length)

    OK, you have made a start to having your Desk Mic Set Up – Next step is to do the soldering for the Yaesu 8 Pin Plug – Here are the Pinouts that need to be used :

    Pin 8 - is the MIC + wire from the XLR plug (Pin # 2) which was a Red coated wire on my set up …

    Pin 7 – is the MIC – wire (Mic Ground) from the XLR plug (Pin #3) which was a clear coated wire on my set up …

    Pin 5 – is the Mic Plug GROUND from the XLR Plug (Pin # 1)

    I have wired my set up in the fashion using a stereo plug and socket in the line about 150mm from the 8 pin plug so that I can plug in a head set mic if required ….

    The FOOT SWITCH has been wired to the RCA Plug on the Rear Panel of the FT-950 – making it easier to wire the 8 pin plug at the front and negating any feedback from incorporating the foot switch into the 8 pin plug.

    I have had some trouble with other forms of wiring for these XLR Mic’s – enough to make one very frazzled – but NOW I have Eliminated any form of HUM, BUZZ, SQUEAL, SCREACH, ETC from the Outgoing Audio and have some very good audio reports from operators near and far ….

    I hope that this information may be of some use to other operators of Yaesu Transceivers (Other 8 pin plug Yaesu’s may be wired different).

    I will accept no responsibility for any damage caused by this or any other modification to Yaesu equipment …

    VK2MTC :cool:
  2. AC0OB

    AC0OB Subscriber QRZ Page


    "I have had some trouble with other forms of wiring for these XLR Mic’s – enough to make one very frazzled – but NOW I have Eliminated any form of HUM, BUZZ, SQUEAL, SCREACH, ETC from the Outgoing Audio and have some very good audio reports from operators near and far …."

    Please give us some background on your reducing the buzz, sqeal, screech, etc.

    I assume the mike had a transformer making it a balanced output circuit? Most mike input circuits in these portable transceivers seem to be 500 ohms impedance using electret elements with single ended phantom power from the same center conductor as the audio.

    Was there enough audio from the mike to feed the audio input circuit or did you have to provide some additional gain?


    Phil - AC0OP
  3. W9GB

    W9GB Ham Member QRZ Page

    Please give us some background on your reducing the buzz, squeal, screech, etc. - Phil
    Phil -

    I agree.
    Hum and buzz (50Hz/60Hz and it's harmonics) occur in unbalanced systems when currents flow in the cable shield connections between different pieces of equipment. Hum and buzz occur in balanced systems when the ground voltage differences between different pieces of equipment are so large that the Common Mode Rejection of the input stage of the receiving device is insufficient to reduce the noise signal to in-audible levels.

    A professional XLR audio (microphone) connector is normally BALANCED.
    Almost all amateur radios use UNBALANCED inputs. That has to be addressed (transformer, etc.) --
    just like with a balanced (half-wave dipole) antenna and an unbalanced (coaxial) feedline.

    Heil Sound deals with this issue in their microphone products and accessories.
    Audiophiles consantly talk about this subject!

    Jensen is best known for the professional transformer solution

    As you noted (Icom especially) use Phantom power on the radio's microphone line that will destroy an unprotected dynamic or magnetic bobbin element -- making the type of noises reported by VK2MTC
    Last edited: Mar 17, 2009
  4. AC0OB

    AC0OB Subscriber QRZ Page

    I was attempting to get more detailed info about this

    My experience with noise reduction is that I interface the balanced mike using either an op amp (if I need gain) or using an isolation or impedance transformer with RF beads and then feed the unbalanced output.

    Just trying to compare notes.
  5. IZ7KHR

    IZ7KHR Ham Member QRZ Page

    I'm very interesting to this thing. I have a ft950, I'd tried to link a studio mic to 8 pins connector, but, only after some solders, I have found a compromise with the noise....
    so, I have seen Jensen site, but I don't know what is the correct product!!!
    Please, anybody have idea about it??? 73 de iz7khr,Frank.
  6. AC0OB

    AC0OB Subscriber QRZ Page

    Mike circuits

    Most studio mikes are 150 ohm impedances with the electret mike circuits having an 500 ohm to 600 ohm impedance, so a 150 to 600 ohm mike transformer such as the JT-16-X series does well. If the mike is a condenser mike, don't forget the 6.81k pullup resistors on the primary.


    One can also reverse the JT-MB-D.



    Study the application notes for RFI mitigation as well in the app notes above found in the [FONT=Helvetica, Arial, Verdana]General Interfacing Application Schematics and the [FONT=Helvetica, Arial, Verdana]Equipment Upgrade Application Schematics[/FONT]



    Last edited: Mar 25, 2009
  7. IZ7KHR

    IZ7KHR Ham Member QRZ Page

    ok Phil, thank you very much for infos!
    I'm very interesting to this argument! so if I would use a studio mic I must adapt it with a 150:600 ohms transformer! But I hae had also some problems with simple dinamic mics, I had to solder many times the 8pins connector to reduce noise into the modulation. Now it's ok, but there is little noise yet...
    the dinamic capsule is a 600ohm unbalanced!
    73 and thanks for infos...Frank iz7khr.
  8. AC0OB

    AC0OB Subscriber QRZ Page

    Wiring Mikes

    I don't know what kind of noise you are hearing (RF feedback, AC buzz, etc) but I would use this circuit:

    http://www.jensen-transformers.com/as/as002.pdf which uses the JT-11P-1 1:1 isolation transformer.

    wiring pins 2,3 of the XLR connector (from the dynamic mic element) to the input of the JT-11P-1 transformer with ferrite beads on the input leads (Red, Brown) and the output leads (Yellow and Orange). I would also use the suggested damping network as well. Depending on the mic input circuitry of your rig, you may need a DC blocking capacitor at the output side of the isolation circuit; I recommend bipolar electrolytics with the proper voltage rating.

    As I stated earlier, look at the application notes such as this one for noise mitigation:


    Using these isolation transformers is a good way to reject common mode noise.
    Last edited: Mar 25, 2009
  9. AE5JU

    AE5JU Ham Member QRZ Page

    You guys are making it too complicated.

    Pin 1 is ground. It is also tied to the shield in the cable, and back to the body of the mic. This should go to chassis ground on your plug to the radio.

    Pins 2 (Sig +) and 3 (Sig -) are the balanced output of the mic. But you don't have a balanced input to the radio.

    Simply tie either of these pins 3 to ground, and the remaining Pin 2 will be your signal wire.

    The difference is impedance is not significant, you don't need a matching transformer.

    KF9UB likes this.
  10. AC0OB

    AC0OB Subscriber QRZ Page

    Mike Circuits

    Not complicated at all if you have common mode noise.

    The circuit I recommended is a balanced to unbalanced circuit and works fine for dynamic element mikes 200 to 600 ohms.

    For most ricebricks, all you need is about a 0.33 uFD decoupling capacitor on the right side feeding the audio to the rig.

    Phil - AC0OB
    Last edited: Apr 25, 2009
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