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Using Ceramic / Crystal Mics on New Radios




 
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Author Topic: Using Ceramic / Crystal Mics on New Radios  (Read 938 times)
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WA2SQQ
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« on: October 12, 2017, 11:05:40 AM »

So Ive used a JFET Source follower to match my D-104 to my Flex Radio works fine. I recently found my old Turner 454X which I believe had an impedance of ~ 50K. Got two questions:

1.   What is the easiest may to actually measure the impedance of the mic?
2.   Can I use the same JFET Source follower and just drop the input resistor to, say 50K to 100K?
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N1BCG
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« Reply #1 on: October 12, 2017, 11:28:52 AM »

This is a very popular question, particularly with the number of newer rigs being used with older Hi-Z microphones.

It has to be said that no microphone should be tested with a resistance meter (VOM) because it won't produce a meaningful reading and the microphone element may get damaged by introducing a current, even a small one.

The best way is to locate the manufacturer's data for the recommended load impedance, which is often a range. Another way which is a bit trickier is to vary the load resistance to match the design frequency response and output voltage. Clearly the latter method is quite involved and requires specialized equipment.

Your idea of using a matching resistor is reasonable.
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W2NBC
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« Reply #2 on: October 12, 2017, 12:18:49 PM »

The "X" on your 454 identifies it as a crystal element. (very high impedance). The source follower will work FB!



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MikeKE0ZUinkcmo
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« Reply #3 on: October 13, 2017, 06:51:41 AM »

I would use a simple test setup and establish a 1KC audio source set to a level of 94db SPL.   Replace the SPL meter with the mic element  placing the face of the diaphragm at the same location as the SPL meter  was.   Measure the element's output with a 10 meg Ohm meter, then substitute load resistors, starting at 10 meg Ohms, and reduce resistance until the element's output drops 6db.  That's the elements source resistance.  Don't forget the meter's 10 meg Ohm input is in parallel with your added load resistor.

All that said, I'd just do as Clark suggested, try the circuit you used for the D-104, it'll probably work fine.



Click pic for more..

Mike

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WA2SQQ
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« Reply #4 on: October 13, 2017, 03:08:23 PM »

Neat idea, that I can certainly do. Thanks
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WD4DMZ
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« Reply #5 on: October 13, 2017, 04:35:12 PM »

Good afternoon. I'm currently using un-amplified crystal D104s on my Viking 2 and Collins KWM2 with good reports. No issue here.

I also have a few amplified D104s and questions for the experts:

1- What is the output impedance of these? Low? High (10,000+ ohms)?

2- Would the amplified version be ok to use on the V2 or KWM2?

3- Would they be ok to use on modern radios?

My concern is over-driving the audio input circuits.

Any advice would be appreciated.

Rich
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MikeKE0ZUinkcmo
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« Reply #6 on: October 13, 2017, 08:10:08 PM »

Hi Rich,

The output node of these amplified mics is the wiper of a 5K Ohm pot, so the output resistance will be at most around 5K.   

The original purpose of the "amplifier" was to  allow the Hi-Z mics to be used with the low input impedance of CB radios, so they were intended as an impedance converter.   I never measured one of the amplified mics to see what the maximum output level is, but it should be sufficient to still use on old gear as well as modern radios.   In any even t I'd think most any rig would have some sort of mic gain control, and over driving shouldn't be a problem.

Mike
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DMOD
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« Reply #7 on: October 17, 2017, 05:00:28 PM »

Stu has some interesting results from an experiment:

http://amfone.net/Amforum/index.php?topic=9100.0


Phil - AC0OB
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WD4DMZ
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« Reply #8 on: October 18, 2017, 11:21:50 AM »

Thanks for the info Phil. Great data.

Back around 2010 I ordered two of the Kobitone crystal elements referenced in the thread to use in a bad D104 head and to make a handheld mic for my Collins. They were very inexpensive and worked great.

Unfortunately the elements are no longer made. I wish that I had purchased a few more. Does anyone know of available Hi-Z elements to use as replacements? Nothing at all at Mouser any more.

Thanks, Rich
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WA2SQQ
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« Reply #9 on: October 19, 2017, 08:38:53 AM »

So I have another question. I'm using my original Crystal D-104 with an MPF-102 interface feeding my Flex 6500. It works fine. I also have one of the newer amplified "Silver Eagles". Does that version use a crystal element or the often mentioned ceramic element? Is there any way to visually tell them apart?

Been playing around with alternate mics. I found a new "crystal" element made by Argonne that Lafayette sold for .99 cents, along with the receipt when I purchased it in 1968. It sounds remarkably close to the crystal D-104. To bad I did not more! I've been tod that this was the same element used in the "Green Hornet" mic Lafayette sold for $4.95
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WD4DMZ
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« Reply #10 on: October 19, 2017, 08:07:18 PM »

One of my D104s is the Silver Eagle. I compared the head with two other amped versions and two un-amped versions and all have the same nameplate except the Silver Eagle which has 'Silver Eagle' in place of 'D104' so it could be different. But, looking at an old catalog the ceramic version is a D104-C. Comparing the specs the Silver Eagle has the crystal version, not the ceramic.

Many years ago I had a Green Hornet but it is long gone. However, I still have the Olsen Electronics by Calrad version in gray and remember paying about $5 for it. Last winter I was chatting with someone, Clark (BCG) I believe, and swapped it for my D104 on the Viking 2 and Clark said subjectively it was very similar in sound but not quite as pleasing as the D104. Also tried an old Olsen 'Chrome Dome' with a series parallel switch for its 2 elements and it was not as good as either. Also tried an old Astatic 531 hand mic which has a much narrower frequency response.

Back to the D104s, the freq response of the amped Eagle is listed as 200 to 20 Khz compared to the un-amped 30 to 7500 Hz.
The amped non-Eagle response is listed as tailored 100 to 6500 Hz.

The D104 crystal element is part # MC 320 and the ceramic as MC 321. Maybe that # is stamped inside the head some place.

Too much info...

At some point perhaps I will find a studio or commercial recording mic to try on the V2.

Rich
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DMOD
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« Reply #11 on: October 20, 2017, 01:17:47 PM »


...At some point perhaps I will find a studio or commercial recording mic to try on the V2.

Rich


The Shure 450 Series II dynamic mics, in the High Impedance switch position. has been an excellent performer for me for all of my vintage transmitters.

It has the just the right presence range peaking for those classic's.


Phil - AC0OB




* Shure 450.pdf (490.83 KB - downloaded 20 times.)
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WD4DMZ
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« Reply #12 on: October 20, 2017, 05:06:01 PM »

Good recommendation. Thanks Phil.

Rich
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WD4DMZ
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« Reply #13 on: October 20, 2017, 05:16:01 PM »

Phil: I was looking thru my collection of mics and I have a Kenwood MC 50 with a L0-Z/Hi-Z output. This mic was purchased new in 1981 for use on my new TS 530S. On the 530S I used it in the Lo-Z position. How do you think this would work on the Viking 2?

Rich
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DMOD
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« Reply #14 on: October 20, 2017, 07:40:27 PM »

It is worth a try.

Switch it to Hi-Z position and see if it has enough voltage drive for the rig.

Phil - AC0OB
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WD4DMZ
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« Reply #15 on: October 21, 2017, 07:57:01 PM »

This thread inspired me to look into my dusty collection of mics for a possible crystal or ceramic element. What I found that intrigued me was a Shure with a 'magnetic controlled' element #99B86. Research showed it to be a hi-Z element that is highly coveted by harmonica players.

I tried it out on the V2 today and it worked well. The report I received when comparing it to the D104 I usually use was that the Shure was clearer and had more higher freq response. Another ham made an audio file so I could hear for myself.

While it is good for use with the V2 it still lacks the full sound I am looking for.

So, back to the accumulated mics I have to see what other surprises I might find.

Rich

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