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Unexpected Interesting Reward!

Dmans

Dmans

Sr. Member
Jan 22, 2017
1,478
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Georgia
I wasn't expecting anything in return for my recent efforts on a friends 148GTL-DX but he surprised me with a Shure 444-Demco Edition microphone. He told me the element was no good in the microphone but I have a plan and a fix for that. Pictures to come!

73's
David
 
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Below are pictures of the Demco-Shure 444 microphone.
AE826CA0-96E6-49AD-8546-A937D3A340BD.jpeg
6D30C0D7-E5E0-435A-9107-3EE1D3EA49AB.jpeg

And here is my cure for bad microphone elements.
1CCD3F22-6D0C-417B-BABB-DDA0BC7B8767.jpeg
1E38EF18-74EC-47C8-8837-6662BAD7A09F.jpeg

Above is an Adafruit product. It is a model “MAX 9814”. I have installed one of these in the stock microphone of my 980 SSB and it really woke the radio up. In the 980 it is powered from pin 6 of the stock mike jack. I did have to replace the cord on the mike with a cord with 5 wires to make it happen but it is worth the effort.

I installed one of these in a friends Turner Plus 3 ( I call it a Turner Plus 3 +) to replace a bad element and it made a world of difference!

The Adafruit Max 9814 has a built in AGC circuit as well as programmable output (via jumpers) for 40, 50 or 60 dB gain. I have found that 40 dB gain is more than plenty and have used a resistor in series with the audio output to avoid over driving or squeal. The resistor value has been determined by trial and error. I believe the resistor I used on the 980 SSB was 150k ohms.

For about $8.00 it’s hard to beat!

Happy experimenting!

73’s
David
 
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Dmans said:
Below are pictures of the Demco-Shure 444 microphone.
View attachment 29682
View attachment 29683

And here is my cure for bad microphone elements.
View attachment 29684
View attachment 29685

Above is an Adafruit product. It is a model “MAX 9814”. I have installed one of these in the stock microphone of my 980 SSB and it really woke the radio up. In the 980 it is powered from pin 6 of the stock mike jack. I did have to replace the cord on the mike with a cord with 5 wires to make it happen but it is worth the effort.

I installed one of these in a friends Turner Plus 3 ( I call it a Turner Plus 3 +) to replace a bad element and it made a world of difference!

The Adafruit Max 9814 has a built in AGC circuit as well as programmable output (via jumpers) for 40, 50 or 60 dB gain. I have found that 40 dB gain is more than plenty and have used a resistor in series with the audio output to avoid over driving or squeal. The resistor value has been determined by trial and error. I believe the resistor I used on the 980 SSB was 150k ohms.

For about $8.00 it’s hard to beat!

Happy experimenting!

73’s
David
Click to expand...
That's a neat little element, I am going to get a couple. I wonder if a 9v battery would run it? I have an old Galaxy hand mic this would be perfect.
 
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Shadetree Mechanic,
A 9 volt battery does a great job. That is what powers the unit in the Turner Plus 3 +. I powered it from the 980SSB mike socket because the voltage was available and the hand mike was small. I did use a dropping resistor to get the voltage down around 5.5vdc on the Turner and can't remember what voltage the 980SSB unit is running at. It seems the unit will operate from 3-9 volts but I can't recall for sure. You can find the specs on Adafruit's web site or Mouser Electronics. Audio frequency response is very wide as well.
73's
David
 
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I checked out the specs and it is capable of putting out several volts. I wonder what would happen if this was used to direct inject a radio? The AGC might work out perfectly. Maybe with an attenuator to dial it in. Now I am thinking....
 
(y)

The AGC does work well. I have not messed with the "AGC recovery" timing but the microphone element is sensitive and even with the 40db gain jumpered you will probably still need a resistor in-line with the audio lead to cut it back some. I have not installed one of these in a desk mike with a gain/sensitivity potentiometer (the Turner Plus 3 + potentiometer was defective so I bypassed it) but the Shure/Demco will be the first one I will try. It will still need an in-line audio resistor I am sure but wiring the pot in-line with the audio lead should allow some restriction in the audio power as needed.

A cheap, fun, useful project for sure!

73's
David
 
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Dmans said:
Above is an Adafruit product. It is a model “MAX 9814”. I have installed one of these in the stock microphone of my 980 SSB and it really woke the radio up. In the 980 it is powered from pin 6 of the stock mike jack. I did have to replace the cord on the mike with a cord with 5 wires to make it happen but it is worth the effort.

David
Click to expand...

I might try this but, I find your last sentence confusing. If the 980 is already a 6 pin cable stock why go down to a 5 pin?
 

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