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Author Topic: Base Microphones for Icom Rigs  (Read 435 times)
KA3NXN
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« on: May 25, 2004, 01:07:10 PM »

Hi all,

I am looking for a suggestion on a good base mic for an Icom rig. Anybody ever try a D-104 or an old Turner +3? I know Icoms are particular about what types of mics you hook up to them. I don't want to spend too much.
 
       
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NA4IT
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« Reply #1 on: May 25, 2004, 02:03:38 PM »

Ah yes the good ol Icom Desk mic question! Well, my friend, you have come to the right place!

Icoms "prefer" electret condenser mics. The rigs typically have a positive voltage traveling on the mic hot line to power that element. Therefore, it is best to run an electret type mic. Here to fore the Icom desk mics, a Icom dedicated Heil mic, or some of the other garden variety desk mics made by MFJ and others that will work with Icoms.

Problem with running another type mic...(1) not enough audio & (2) possible burn out of the B+ on the mic + line, rendering even the hand mic useless.

Careful my boy, Careful...
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KT8K
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« Reply #2 on: May 25, 2004, 03:30:47 PM »

Hope you don't get a stiff neck or back bending over to get close to that desk mic.  I prefer a boom stand that puts the mic right in front of my face - much easier on the old bod during contests or long ragchews.
73 de kt8k - Tim
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W3JJH
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« Reply #3 on: May 25, 2004, 04:01:43 PM »

Actually, there is no power on the mic signal line on most Icom radios.  An 8-V supply line is brought out separately on the 8-pin microphone connector.  The drain resistor for the electret's charge convertor is connected between the mic signal line and the 8-V supply.  This arrangement allows unpowered microphones (such as dynamics) to be used with the radio.  Of course, Icom radios are notorious from low mic preamp gain, so it's a good idea to use a 10- or 12-dB preamp with most dynamic microphones.  (The 756 Pro and Pro II are exceptions to that rule.)  The 8-V supply can be used to power a one transistor preamp built into the mic connector.  It can also be used to power the preamp in amplifed D104 microphones.
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N3ZKP
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« Reply #4 on: May 25, 2004, 04:11:21 PM »

Forget the desk mike. Use the appropriate Heil mike on a boom or, better yet, use the Heil ProSet headset/mike combo.

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W2NSF
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« Reply #5 on: May 25, 2004, 04:39:19 PM »

You didn't say which model ICOM, so I'll assume it's one of the later ones.  My vote is for the Heil ICM.  Just add one of the many available accessories and you can have a desk, boom, or just plain hand-held version.  From my first-hand experience, it's a good mike for an ICOM.
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K0BG
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« Reply #6 on: May 25, 2004, 05:34:06 PM »

Let's fix an error reported earlier. While it's true most newer model Icoms have a separate 8V supply available at the mic jack, there is also 8V on the mic's input line to power mic, and has been since the IC701.

You can short out the mic line with out too much worry, but if you short out the separate 8V supply, you're in for an expensive repair.

Alan, KØBG
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N4ZOU
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« Reply #7 on: May 26, 2004, 01:46:45 AM »

A Radio Shack electret Microphone element works fine for the 756 PRO and PRO II as is. Older Icom's need a little preamp to boost the output of that same element but if you open the hand mic you don't find one there as you would have the hand mic very close to your mouth. Radio Shack has two versions. The two lead one hooks up to pin 1 and 7 on the mic plug on front. Hot lead to pin 1 and ground to pin 7. The three lead element needs a .1 uF capacitor between pin 1 and the hot lead and the ground pin goes to pin 7. The power lead hooks to the +8 volt supply pin 2. If you have the room in the Mic head put a 10 uF and a .047 uF across the Hot and ground leads of the Mic element. This chokes off stray RF that might get into it. Also put a 2K ohm resister in the lead between pin 2 and the power lead going to the microphone element. This prevents shorting out of the internal +8 volt power supply if the mic element shorts out. The circuit is shown in the manual if your Icom came with a hand mic. It's a little diffrent in that the hot and power lead is connected to pin 1 and the hot lead of the mic element has a .33 uF DC blocking capacitor. I prefer hooking to pin 2 for power. The PTT switch should pull pin 5 to ground which is pin 6 for ptt. BTY, the .1 uF capacitor rolls off audio frequency below 300 hz that you don't need or want and also blocks DC voltage. If your running a Icom that has the voice and cw memory keyer you can get fancy and build the external keypad into the base of a big old microphone base. Thats in the manual also if you have an Icom that supports it. On the PRO II the frequency up and down buttons can be converted to a two button cw keyer. You can get the hang of using them but when I built my own Microphone I included a small 1/8 inch stereo jack connected to these two switches. A 470 ohm resistor is added to one side of a key for setting dit or dash according to your left or right hand requirment. I found I did not like connecting my key to the 1/4 inch connector on the front of the PRO II so I just use the up/down frequency button connections. This also allows your key to run the frequency up and down when selected from the menu.
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W3JJH
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« Reply #8 on: May 26, 2004, 10:44:54 AM »

K0BG is correct in pointing out that most (but not all--my son's 746 for example) recent Icom radios have a drain pullup resistor connecting the MIC signal line to 8 V.  The usual value seems to be 1 k.

One should always verify check for the presence of power on any microphone input and verify compatibility before connecting any microphone to any radio.
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KA2UUP
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« Reply #9 on: May 27, 2004, 11:36:37 AM »

I use a D-104 with a TUG8 base with no problems.  Just keep the MIC gain as low as possible.  I also use an SM-20 from ICOM, but it all depends if you want to spend the bucks.

Good luck DE Bert @ KA2UUP
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