FYI: Mics and IC-7300

Discussion in 'Microphones, Speakers & Audio Processing' started by K4EM, Apr 12, 2017.

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  1. K4EM

    K4EM XML Subscriber QRZ Page

    I recently purchased my first Icom radio an IC-7300. I have several Dynamic mics and several Electret mics on hand. I made a mic cable and added a 1uf 50v blocking cap, that's all I had. I connected my RE27 and went through the mic gain/comp adj. I found I had to run the mic gain at 90%, I connected my Audio-Technica ATR30 and had to run it at 100% gain and it didn't work too well. I then tried my 2 electric mics; a Yamaha CM-500 uses pin 1 voltage for element, final gain 20%; my handmade EM1a electric (requires +48v Phantom power), gain 25%. Both electric's worked very well and I received excellent audio reports. Compression set to '2' for both electric's.
    I know Dynamic mics output is lower versus Condenser/Electric mics but I never researched or knew what it was. So this is what I found from this web-site, I assume it to be accurate.
    Based on the output voltage and versus mic gain of my mics you can quickly see which should work without too much gain. Personally I don't want to run the mic gain above 85% on the Icom, I would prefer to have more headroom. The 'PA' is a standard mic parameter 'Pascal's', google that for more info.

    Dynamic mics mic gain will most likely have to be 85 to 100%
    Behringer XM8500 .3mv/PA
    EV RE-27 3.1mv/PA
    EV RE-20 1.5mv/PA
    Shure SM-58 2.6mv/PA
    Audio-Technica ATR30 1.4mv/PA
    Heil PR40 2mv/PA
    Heil PR30 2.3mv/PA

    Condenser/Electric mics
    Behringer B1 20mv/PA
    Behringer C1 22mv/PA
    Behringer C2 8.9mv/PA
    MXL 990 15mv/PA
    MXL V67G 15mv/PA
    MXL R144 (Ribbon) 1.6mv/PA
    MXL V69XM (Tube) 40mv/PA Big output

    A ham friend who bought a IC-7300 last year looked at the schematic and determined he could use a small mic preamp, output set low, into the front mic jack. Versus using the 'ACC' mic input connections. He has not tried this yet, does anyone have an answer?
    So following Icom's convention of using Electric mics with there rigs I am going to use my 2 Electric's and not bother with a Dynamic, adding a small preamp, in my opinion really wouldn't be worth it for me.
  2. KE0ZU

    KE0ZU Ham Member QRZ Page

    And now you know the output level differences between the various microphone types. They also have different termination impedances, and the FET (electret/condenser) mics require power to operate.

    I use a single microphone with an adjustable gain amplifier. This allows me to use the same mic for every thing, regardless of the mic type or radio used.
    Last edited: Apr 15, 2017
  3. G3YRO

    G3YRO Ham Member QRZ Page

    By the way, you keep saying "Electric" mics, when I think you mean Electret ! (they are a cheap form of condenser microphone capsule, that only need a very low voltage to work - and ideal for ham radio use, given our narrow bandwidths)

    Roger G3YRO
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  4. KE0EYJ

    KE0EYJ Ham Member QRZ Page

    FYI, I suggest following Bob Heil's recommendation on the 7300. I used to think I needed to run my mic gain up to 100 on my Behringer xm8500, and it turned out that when I dialed it back to 70, or so, the 7300 actually had higher audio peaks on my watt meter. I have no idea why this is. Maybe there is some kind of internal limitation going on in the 7300? Less turned out to be more, for me.

    Bob's words held true. Turn the compression off. Set the mic level so that you are peaking about 50% of the ALC, then turn the compression back on. I prefer using 3 (a big higher than Bob says, but my mic differs from his), and for DX, setting up a narrow bandwidth, and then jacking the compression to 6 to 8, max. You cannot have a noisy room, and go above 6 comfortably.

    My TX EQ settings are around +3 to +4 on the Treble, and -1 to -3 on the Bass.

    In any case, I found that "less is more" when setting up the 7300. As mentioned, something happens that limits what you are doing, if you start using levels above 80, or so.

    BTW, for DX, the hand mic is still my favorite, most of the time. I have verified that it works better for DX, most of the time, by listening to myself through web SDR and also from reports of friends in Europe and Australia. The hand mic rocks for DX. The oddest thing about that mic, though -- the Narrow setting does NOT work well, for DX. Medium, or even Wide, sound better to DX. Again -- verified by myself, using Web SDR, and multiple DX contacts in the 5,000 to 11,000+ mile range.

    For the hand mic, I find +2 Bass, and +3 or +4 Treble works best. I've tried various other settings -- including cutting Bass way back, trying Narrow settings, etc., and Narrow just never works well for me, with this mic. Something about where the strength is, with this mic -- Narrow is weak.
    Last edited: Apr 15, 2017
    K0UO likes this.
  5. W8AAZ

    W8AAZ Ham Member QRZ Page

    I bought an inline transformer that I was gonna try with the RE 27, amongst others. Takes XLR output and steps up to 600 Ohms unbalanced. I guess I would have to put a cap in series. But I have been to lazy to implement it yet. The dinky little plastic hand mic sounds too good!
    KW6LA and K0UO like this.
  6. WA9SVD

    WA9SVD Ham Member QRZ Page

    Most Icom radios typically use an electret mic, so why try to make an easy solution into a major problem? The electret mics typically already have an internal preamp (hence, the need for bias voltage vs a dynamic mic) to provide gain and levels compatible with the Icom radios.
    At least your "dinky little plastic hand mic" is already matched to the needs of your radio!
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  7. KE0EYJ

    KE0EYJ Ham Member QRZ Page

    I get great unsolicited reports from DX (last night, Korea to South Africa, on 100w and a my doublet, no less) using the Icom hand mic. It's just too darn nice, and convenient, not to use!
    W4EAE, K0UO, W9WQA and 1 other person like this.
  8. G0GSR

    G0GSR Ham Member QRZ Page

    What it all boils down to is that Icom designed the internal mic pre-amplifier to have a gain which was suitable for the output level of an electret microphone.
    In general, dynamic microphones have around 20dB less output and so are unsuitable for use with the IC-7300.

    Remember also that modern DSP type radios do not have a conventional microphone gain control.
    I.e They don't have a physical or electronic attenuator within the analogue stages.
    Gain control is achieved by digital scaling of the sampled audio. In my view, a high level of digital scaling is going to be bad for quality so the lower the setting of the "mic gain", the better in my view.

    Frank, g0gsr
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  9. WD8T

    WD8T XML Subscriber QRZ Page

    Not entirely accurate information. True for older Icom radios but not the 7300 or 756pro's, 7600, 7700, 7800 series. They are designed to accommodate dynamic mics. Dynamic mics work well with the 7300 but not all dynamic microphones have the same output. I'm using two Heil dynamics including a 14 year old goldline GM4. I can run it at 60-70 % mic gain on the 7300 and keep it wihin alc limits. No issues either with a Proset headset.
  10. KE0EYJ

    KE0EYJ Ham Member QRZ Page

    The Dynamic mic works fine with the 7300, also. But, as Bob Heil said, you have to not be afraid to use the full range of the mic gain to use one. He's right. And, I will add -- it helps to add about level 2 or 3 compression.

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