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Icom Mic oddities

Discussion in 'Microphones, Speakers & Audio Processing' started by K4TFL, Nov 20, 2021.

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  1. K4TFL

    K4TFL Ham Member QRZ Page

    So I have an IC-7610 and a 7300. I've used both with a Shure SM7B (might be swapping to something else). But the two HM-219's that I have from each radio only work on the 7300 and not the 7610. I get no audio on monitor into a dummy load on the 7610.
  2. W9GB

    W9GB Ham Member QRZ Page

    The Icom IC-7610 is an aircraft carrier transceiver, with multiple menus,
    including functional operation of its front panel 8-pin Microphone connector.

    Since you were using other non-Icom microphones (Shure SM7B is a Dynamic microphone) you may have forgotten to Check the IC-7610 Menu !
    ** WARNING : Failure to Block DC Voltage from Icom transceivers, when using non Icom microphones CAN damage the radio ($$) or the microphone ($300 for a Shure SM7B) **

    Shure SM7B Cardioid Dynamic Vocal Microphone
    User Guide
    , (specification sheet attached below)
    The Icom HM-219 microphone uses a Elecret (Condenser) element !!
    Icom branded microphones, for the past ~40 years, use Condenser (Elecret) elements that require DC voltage (+8 VDC) on the MIC Audio lead (Pin 1) to operate.
    Icom IC-7610 HF/50 MHz Transceiver
    Basic Manual (80 pages)

    PAGE 8-7
    MIC Input DC Bias (Default: ON)
    Outputs the 8 V bias voltage (approximate) from the microphone connector (pin 1 of [MIC]).

    PAGE 13-3
    Connector Information : Microphone
    NOTE: Pin 1 outputs 8 V DC power for Icom microphones.

    You can turn OFF the DC power when you use non-Icom microphones
    in the “MIC Input DC Bias” item on the CONNECTORS screen.

    Attached Files:

    Last edited: Nov 20, 2021
  3. K4TFL

    K4TFL Ham Member QRZ Page

    That would explain it, I had the input bias off when testing the Icom mics. The odd thing is the pin out shows pin 2 as 8vdc. I just modified a Daniel Clark headset to work (so I don't annoy the wife) with either radio.

    Thought the Heil cable I'm using allowed the 7300 to use the SM7B, which doesn't have the option to turn of the bias voltage. At least not that I could find. I don't remember turning it off on the 7610 when I was getting it setup, but it is possible.
  4. W9GB

    W9GB Ham Member QRZ Page

    Compatible Microphones for Icom Radios (circa September 2020)
    by Heil Sound

    Heil Sound normally installs a DC Blocking capacitor inside their non-condenser (Dynamic) microphones, EXCEPT for their high-impedance (Hi-Z) GM “Vintage” model.

    I can not remember, IF Bob placed that same protection within the XLR-adapter cables for Icom Radios. Heil Sound has published the following information (below) for at least 25 years.

    All Things iCOM
    Microphone Basics

    DC De-coupling on Icom Rigs
    IF you do not have a Heil Sound microphone, THEN you need to do the above modification.

    All ICOM transceivers utilize “phantom power” on their microphone inputs.
    Borrowing technology from the recording studios, DC power is applied via the mic line to energize the electret elements used in stock Icom microphones.
    At the same time, DC flows DOWN the mic cable while the mic audio is fed UP the same wire. Of course, the voice signal is AC, so DC flows one direction while AC flows the other direction – all on the same cable. This is pretty cool until you start having RFI problems, but we shall ignore that possibility for now.

    The BIG problem with this is when you try using a REAL (Dynamic) microphone.
    Connecting a dynamic into your mic input will provide a nice short of the +8V DC power straight to ground. SMOKE CITY!!! ($$)

    To use any Dynamic element on these phantom powered inputs (which should NEVER be applied to a mic input of a radio transmitter, IMHO), the input must be de-coupled so the mic audio AC signal can pass through to the mic preamp, while simultaneously blocking the DC voltage from reaching that mic element.
    Simply install a 1 µF non-polarized tantalum capacitor in series with mic lead. You may get by with a .68 F or a .47 uF, but anything less (.01 µF, .005 µF, etc.) will not pass any speech audio worth listening to). The cap MUST be a non-polarized type.
    This will keep the DC factor into the mic preamp circuitry. But, you don’t need to worry about that so long as you purchase the correct adapter cable to go with your dynamic microphone.
    Please see our adapter selector to find the right cable for your rig.

    Heil’s Amateur Radio specific microphones (non-3 pin XLR) have a 1 µF capacitor installed.
    All AD-1 boom set adapters have the decoupling capacitor installed in the 8 pin Foster connector.
    The coupling capacitor is NOT installed in our new high-impedance GM “VINTAGE” microphone, as this model should NEVER be used with ICOM low impedance inputs.
    Last edited: Nov 21, 2021
  5. K4TFL

    K4TFL Ham Member QRZ Page

    I have the Heil CC-1-XLR-IB cable. It specifically stated it had the blocking capacitor on gigaparts when I ordered it. Haven't had any issues with the SM7B on the 7300 or 7610. As stated in previous post, the 8vdc was turned off on the 7610 which is why the hand mics didn't work. I just don't remember turning it off when I was setting the radio up. I also had a migraine at the time, but wanted to play with my new toy.
  6. G0GSR

    G0GSR Ham Member QRZ Page

    Mr Heil being over-dramatic again.....

    More nonsense..
  7. W9GB

    W9GB Ham Member QRZ Page

    You need to read the Tech Forum Q&A on Microphones here, for the past 20 years …
    Typical Questions focus on the Lollipop (Astatic D-104) …
    Little electronics knowledge (theory or practical construction) … “Wire to color”, most popular.
    You would trust that person to wire an electrolytic capacitor correctly?
    KB0MNM likes this.

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