[AMRadio] Dreaded D-104

[Jay Bromley]

Hi Guys,

I have two non-amplified D-104's and another one known as the Silver Eagle
with an amplified module in the base.  I bought the SE thinking the push bar
would be nice, not knowing the Grip to Talk bar was linked to the PTT bar
making it harder to depress the Grip to Talk.  Anyway all of these were
bought new right before Astatic quit making them.  I have compared them to
the older D104's crystal elements and heard no difference in between old/new
elements.  Neither has the response plot graph changed for the crystal head
during that time.  

All the above microphones came with the built in pre amp, that was mainly
added to drive the newer low impedance solid state rigs.  In my humble
opinion the frequency response with these amplifier modules was horrible,
unless you like having tin can audio!  Over the years I have taken the stock
audio board out in base of the microphone and  wire straight to the D104
head.  I have also modified a few of them for better performance over stock
head alone.  

Someone spoke of looking at the response curves and that is an excellent
idea.  That is the first thing I would do!  On the amplified D-104 with a
crystal element, the response curve of the Astatic sheet had a rise starting
at 1KHz and peaked 10 dB around 3KHz and then rolled over a -10 dB at 7 KHz.
That wasn't too bad as it was like the non-amplified D-104 on the high end.
The bottom end of the amplified base was severely affected below 1KHz if you
want to call that the low end, hi.  The D-104 at 1KHz was a crossover point
at zero dB with the amplified stand.  Output impedance was spec at 5000 ohms
impedance or less.  Output level was spec at 1KHz again, but depended on the
load even with the amplified module!  The frequency response was rated at
200hz to 20Khz, but looking at the response plot there is nothing flat here.
The low end at 100 Hz was just -10 dB, but was dropping the whole time from
1KHz on.

When comparing microphone or microphone elements it sure helps to compare
these response plots!  Then you can fit the microphone to your voice and
what you want to sound like.  I get a huge kick out of this chest beating on
which mic is the best!  It really depends on your voice and what you are
trying to sound like.   Some guys can sound great on a Shure 444, I have one
friend that sounds great on his, but he has huge vocal toobs and worked in
broadcast many years ago.  The last time I looked at the response plot for a
Shure 444 was very tight and would not work for me.  When I am chasing DX I
don't mind using a Heil HC-5, but for rag-chewing I would prefer something
wider in response.  I don't rag-chew down into the noise normally and so I
don't need the extra punch of the HC-5 during those times.

On the D104 crystal mic head or Astatic D104 microphones with non-amplified
bases, the response curve or plot depends on the LOAD of the element.  This
has been discussed many times by Don, K4KYV and many others ion this list
over the years.  Here is a very short summary.  With a 5 Meg Ohm load the
D104 is pretty flat on the low end.  From 1KHz to 50 Hz it goes from -1 to
-3 dB on the Astatic spec sheet.  How many NEW rigs have a 5 Meg ohm load?
Even at 500 K ohms for the load it starts dropping off around 300-400 Hz and
is down by -10 dB at 150 Hz.  At 50 K ohms the D104 crystal element drops
like a brick from 1KHz!  Using 50 K ohms to load the D104 element the
response is down -20 dB at 450 Hz!  This is why most folks say a D104 sounds
tinny while trying to use them on new rigs with even lower impedance!

The temperature range is interesting for the Astatic Crystal element is -22F
to plus 113F.  Anything higher or lower they say will result in permanent
damage to the crystal element.  Makes you wonder when you see one out in
Field Day in direct sunlight and the temperature just hit over the 110 F
mark.  That would put that chrome housing well over that.  Overall
considering the ones I have used over the years, the elements use are pretty
rugged I think.

Ok considering all the above.  I have now modified two of my D104 to W9AC's
design.  I have pretty much copied or adapted the schematic that is one
Paul's QRZ.com listing for his call sign.  Paul may want to comment more on
this, but the idea is to show a high impedance load to the D104 element
without loading it down and provide a nice low impedance drive for the newer
rigs.  On my SSB rig you now would be hard pressed to tell the difference in
my modified D104 and a Heil PR781!  I have to use a 3 dB treble boost on the
PR781 and no treble boost on if I use the modified D104 on the same rig!
Again remember you have a 10 dB treble boost with the D104 around 3 KHz, so
I can run the D104 and sound great.  The only difference after the treble is
set correctly between those two  microphones the, PR781 is a little smoother
and is easier to use with the boom mount most of the time.  All D104's had a
metallic sound with that huge metal covering the crystal cartridge.  Some
more than others depending on how you mic the D104!  Really considering how
old the D104 design is, this is really pretty amazing.  I would be glad to
do some on air demos if anyone is interested.  The new guys seem to love
seeing the old beloved D104 on a newer rig and the OTers are shocked when I
show them they can sound very good on a new rig.  BTW, I was not able to
find a response plot for the PR781 to compare it against the stock D104
element.

Many years ago I bumped into Pete W1VZR on 10m that used an FET in the
bottom of his D104.  Nothing new here as even the older handbooks show this
was best to keep from loading down a crystal element using a FET.  Sounded
great and I remember him saying that also did away with a lot of hum as he
didn't need to use as much gain in the first stage of the rig.  It was a
Valiant and not sure now, but Pete could have even bypass the first stage?
Too many years ago, maybe some of you that know Pete could comment further
on this?

If you need the response plot graphs of the D104s mentioned above I can scan
them for you if you like, but bet they are on the web somewhere?  Also I
think I have one of the Astatic 10DA-L Dynamic head.    

The old timers already know this, but if you have a rig with a good
response, you can EQ a mic with good response to make it sound like pretty
much like anything you want.  Like for instance I've have duplicated the
sound of the Heil HC-5 and HC-4 using a Radio Shack electret condenser
element with careful EQing that has a wider response.  There is no way to
make an HC-4 sound like a studio mic no matter how you EQ it!  There is
nothing left to EQ except for a narrow range the HC4 element has.  Same for
a rig, you can put a studio mic on an old military rig and it will sound
much like the carbon mic it was built for.  Maybe a little smoother if you
get the gain right, but unless you flatten out the response of the rig you
are stuck with that sound.

All this discussion without mentioning the response plots, your own voice
characteristics, and what you are trying to achieve is pretty much
meaningless.  Then one also has to consider guys with blown out ear drums
that most anything loud sounds great to them.  Including the distortion they
cannot hear!  You also need to consider what load you are going to use with
a D104 element, that can sure make a difference in your overall sound!  Old
tube rigs vs. the newer solid state rigs are vastly different in the D104
setup and the load they provide to the element!  

One last thought on Astatic element costs comparing them to others.  AES use
to also sell the Astatic elements, if I remember right they were $28 near
the end of the run.  Just something to consider.

I hope some of the above helps the new guys.  Nothing I said is really new
and like I said come ups every few months.  Sorry for book I wrote, but like
everything on AM, nothing is as simple as it seems!  73 de w5jay/jay..