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Author Topic: D-104  (Read 1403 times)
KB3KCJ
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Posts: 125




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« on: April 12, 2010, 04:46:47 AM »

I have a D-104 wired to a Yaesu FT-980.  Everyone tells me that the audio sounds high end and tinny.  Anyone have any suggestions?  Thanks.
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AA4PB
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« Reply #1 on: April 12, 2010, 05:20:05 AM »

Does the D104 have a preamp in the base or is it the standard high impedence model? The radio has a fairly low impedance input that won't work with a high impedance mike.
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NR4C
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Posts: 306




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« Reply #2 on: April 12, 2010, 05:32:04 AM »

I also have a D-104.  I like the looks, but i don't use it any more.  I bought a Heil HM-10 Dual for my Kenwood 570.  Now the old D-104 rests on the shelf, doing what it does best, ...  Look Cool.

...bc   nr4c
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AA4PB
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« Reply #3 on: April 12, 2010, 05:56:30 AM »

You could also purchase a Heil mike element and place it inside the D104 housing.
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KA2UUP
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Posts: 388




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« Reply #4 on: April 12, 2010, 07:55:48 AM »

You have several solutions.

I use a D-104 with my ICOM IC-746.  However, in order to use it, I have to turn the amplifier all the way dwon to the point where it will almost cut off.

Another choice is, like another poster said, use the Heil element.  Heli sells a complete conversion kit for this.

Lastly, you can use an equalizer.  I also use this option and it works well.

Good luck!

KA2UUP
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KB4QAA
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« Reply #5 on: April 12, 2010, 10:01:17 AM »

http://www.qsl.net/wa2mzf/d104.html

The D-104 has a high (very high) impedance crystal element originally designed to work with tube sets.  It was also designed to give emphasis to the higher frequencies between 2k-3khz in order to give it 'punch'.   It was the the speech processor equivalent.

The problem is that modern solid state rigs by the 1960's used low Z mics.  Astatic developed a two transistor amplifier for mounting in the mic base.  It takes a 9v battery and has a volume/modulation adjustment.  It can still sound a bit pinched or tinny.

If you really want the best audio, you can build a very simple FET amplifier which provide a +1Mohm impedance to the crystal, but also amplifies to a level which makes the radio happy.  

http://kd5rug.org/anarchy/PDF/d104amateurradio.pdf

http://www.qsl.net/hcara/Improving_the_D-104_N9WB_rev2.pdf

There are at least half a dozen variants on the FET amp, two or three have been published in QST, as early as 1969 possibly by Lew McCoy.  I recommend a QST search and also on the web to find one you like.  Parts can be had at Radio Shack and it shouldn't take an hour to rig up.

So, don't rip up that D104 needlessly.  You can get great audio from it and help rehabilitate it's reputation.  Oh, it IS possible for the crystal to get damaged by dropping it, or absorbing moisture. But obviously yours is working.

Good Luck.
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W2AEW
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« Reply #6 on: April 12, 2010, 10:32:27 AM »

The other replies have given you good info.  Some sort of impedance conversion is generally required (provide hi-z load for the mic, and a low-z output drive for the rig).  The amplified D-104's have a low-z output, but the preamp is tuned for very little low frequency response.

Simple modifications include replacing the preamp with a simple FET follower generally works pretty well.  You could go as far as you like with this.

I put together a circuit that I use with my D-104.  It has a preamp and active base/treble stages and works pretty well.  It can be found at:
http://www.qsl.net/w2aew/myd104amp.html
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AA5TB
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« Reply #7 on: April 13, 2010, 11:03:29 AM »

As others have already mentioned the need to convert the high impedance to low impedance, I recently built an impedance converter using an N-channel FET into the base to use with my Astatic D-104 and 10-DA microphone elements.  With a high value gate resistor the frequency response is good.  I designed it for about 600 ohms output impedance and it gets DC power from my rig.  On my Yaesu FT-897D the D-104 element sounds the best on AM, the 10-DA is best on SSB, and the stock microphone is best on FM.

73,
Steve - AA5TB
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W0BTU
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« Reply #8 on: April 13, 2010, 12:32:08 PM »

I have a D-104 with the stock preamp on an Icom IC-751A, which works just fine for me. The preamp is powered by a 9 volt battery. There's 8 volts available at the mic plug, and I would prefer to toss the battery and power the preamp with 8 volts.

There's no resistor in series with the battery and collector that can be changed or eliminated. In other words, the change would drop the collector voltage from 9 to 8 volts.

My question is, will the audio quality degrade if I drop the preamp voltage by one volt? I'd like to hear from anyone who has firsthand experience with this.

73 Mike
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