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Author Topic: Headset With Boom Mic  (Read 4182 times)
WB4YDY
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Posts: 12




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« on: December 02, 2012, 09:48:54 AM »

I have a Radio Shack/Koss headset w/boom mic that I would like to use with my IC-756pro3. It is very comfortable with good full coverage headphones but the mic will not drive the Pro3. The audio seems full range and clear, but no "punch", even at 100% mic gain and using compression.

The HM-36 hand mic and a Altec Lansing PC type headset w/boom mic both drive the rig with no problem. In fact, I often get unsolicited, "great audio" reports in the middle of contests using the Altec Lansing headset/mic. But it is a behind-the-head design, small headset not full ear coverage, and is not very comfortable for long use.

I am guessing that my Altec Lansing headset has a electret condenser type mic element and the RS/Koss has a dynamic element. The RS/Koss mic element is about 5/8" diameter, with 2 leads, and would be easy to replace.

Any thoughts and suggestions if I am on the right track to make the RS/Koss headset work with the Pro3 would be greatly appreciated.

If this is the fix, what is good element for this application and where should I look? I would mainly use it for contesting.

Thanks and 73,
Pete, WB4YDY

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NA4IT
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« Reply #1 on: December 02, 2012, 11:16:39 AM »

You are correct in your assumptions. The RS/KOSS has a dynamic mic in it. The mic is being affected by the voltage present on the mic hot wire. You need to put a blocking capacitor in that line, and that may cure your problem. Use a non-polarized 1uF capacitor inline. You should be able to put it in the mic connector.
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WB4YDY
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Posts: 12




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« Reply #2 on: December 02, 2012, 02:34:54 PM »

NA4IT, thank you  for your quick response. In trying to keep my post short, I failed to mention that I am using a very old Icom CC-1 adapter cable with the RS/Koss and Altec Lansing headsets. I don't see this exact cable listed on the Heil website now. Besides a 1/4" female PTT connector, it has a 1/8" mono female mic connector and 8 pin mic connector.

I bought this cable in 2001 for use with a light weight Heil headset w/boom mic. I think it was a BM-10 (?) with an HC-4 element. I just opened up the 8 pin mic connector and do not see a capacitor. If that is correct, then what you say makes sense. The adaptor is passing through the mic voltage which doesn't hurt the condenser element but does hurt the dynamic.

If this still sounds right to you, I can wire a new mic connector with blocking capacitor for the dynamic element in RS/Koss headset.

Thanks again,
Pete, WB4YDY
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AD6KA
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Posts: 2236




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« Reply #3 on: December 03, 2012, 01:29:34 PM »

Have you dropped a note to Bob Heil?
While this question does not involve his
products, I have found he is always willing
to help folks with all things having to do with
microphones.
Just a thought.
73, Ken  AD6KA
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NA4IT
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« Reply #4 on: December 04, 2012, 04:15:16 AM »

You do need the capacitor with a dynamic mic.
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WB4YDY
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Posts: 12




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« Reply #5 on: December 04, 2012, 05:50:33 AM »

Thanks NA4IT and AD6KA for your responses. Since your thoughts (NA4IT) agree with mine, I am going to try the capacitor.
I have everything I need except the 1uf capacitor. I have ordered a few and will hopefully be able to try it before this weekend's 10 meter contest.

Thanks and 73,
Pete, WB4YDY
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KE3WD
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Posts: 5694




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« Reply #6 on: December 04, 2012, 05:46:03 PM »

Blocking cap doesn't necessarily have to be 1uF. 

Two 4.7uF electrolytics or two 10uF electrolytics hooked back to back, both minus leads connected together in series, will yield a nonpolarized cap of one half the value of the two identical caps. 

Most hams can find those values in the junkbox or in some discarded piece of consumer stuff such as old radios, etc. 

Depending on the input impedance of the following circuit, you likely could use a 0.1 uF cap there as well and still pass all of the desired audio frequencies. 


73
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WB4YDY
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Posts: 12




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« Reply #7 on: December 05, 2012, 05:27:12 AM »

KE3WD, thank you for your help. I thought that was probably the case, but wasn't sure. Since I should have the 1uf capacitor tomorrow, I think I will wait and see if I can fit the one cap into the mic connector.

Thanks again and 73,
Pete, WB4YDY
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WB4YDY
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Posts: 12




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« Reply #8 on: December 07, 2012, 01:15:08 PM »

I did a very neat job making a 1/8" mono to 8 pin mic connector adapter, soldering the 1uf capacitor inside the 8 pin mic connector. Only to find there is no noticeable difference compared to without the capacitor.

It was late last night when I was able to test this arrangement. I will play around with some various other value capacitors that I have in my junk tray when I have time.

73,
Pete, WB4YDY
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