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Astatic D-104 Restoration - Dynamic Mic Element Recommendations

Discussion in 'General Technical Questions and Answers' started by KJ5XX, Feb 12, 2009.

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  1. KJ5XX

    KJ5XX Ham Member QRZ Page

    Hey All:

    I have an old Astatic D-104 Mic that I'd like to restore. I want to pull out the old Crystal mic element and preamp and replace it with a modern Dynamic microphone element (not a crystal element). I'd use something like a Heil HC-4 or HC-5, but unfortunately Bob Heil has pulled these elements off the market (people were putting them in microphones and then remarketing them as Heil mics).

    Not sure what specs I should be looking for to make the mic compatible with a modern rig with the sort of freq response/impedanance that would work well and have good audio.

    I have a Kenwood TS-570D, and was thinking that an element with a 600 ohm impedance and freqency response from 50hz-15 or 20khz would work, but am unfamiliar with mic sensitivity specifications.

    Found a site with a number of difference choices and would appreciate some thoughts/recommendations on an element that would be compatible or considerations I need to think about.


    Ron - KJ5XX
    Last edited: Feb 12, 2009
  2. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

  3. W9GB

    W9GB Ham Member QRZ Page

    Ron -

    I do not know what you information source is -- DID YOU CALL HEIL ?
    Bob did stop selling the HC-4/HC-5 elements individually, but the element is available as part of the full HC-104 kit.
    You can also use ANY dynamic (Lo-Z) element (even a Kenwood mic element from Kenwood parts) -- as long as you correctly mount it with a baffle int he D-104 head -- for properly sounding audio.
    Mouser and MANY audio/sound reinforcement suppliers have dynamic elements.
    You can even walk into Radio Shack and purchase a 2 or 3-wire elecret mic element (< $5).
    Elecret element require a power source and need to be properly wired.

    The HC104 Element modification kit ($70 USD) for the Astatic D-104 microphone.
    This kit of parts uses the Heil HC element and still listed on the web site

    For questions contact:
    E-mail Bob:
    Heil Sound, LTD
    5800 N. Illinois St.
    Fairview Heights, IL 62208
    FAX 1-618-257-3001
    E-mail the webmaster (edits/corrections) at:
    Last edited: Feb 12, 2009
  4. KJ5XX

    KJ5XX Ham Member QRZ Page

    Yes, I'm aware that he sells this kit, but I'm not interested in the kit, only an element. Don't see the point in paying $30 for a bunch of foam when the elements used to go for $44. I have a couple of Bob's elements that I've used to restore other mics, but they're as rare as hen's teeth these days - unless you want to purchase the kit (which I don't). Nothing against Bob - his stuff is the best, but not willing to pay that price.

    W9GB said:

    Mouser and MANY audio/sound reinforcement suppliers have dynamic elements.
    You can even walk into Radio Shack and purchase a 2 or 3-wire elecret mic element (< $5).
    Elecret element require a power source and need to be properly wired.

    Yes, Mouser has a number of dynamic elements - all of which have different characteristics (sensitivity, etc.). I guess what I'm looking for is advice on how important sensitivity is on choosing a proper ham radio element, and out of the choices they offer, not sure which one would be the best option.

    Could go with an electret element via RatShack, just not sure what sort of audio quality I'd get - just looking for the best solution.


    Ron - KJ5XX
    Last edited: Feb 12, 2009
  5. W9GB

    W9GB Ham Member QRZ Page

    The search for the "best microphone" or "best sound" is like looking for The Lost Chord :)
    IF you desire your voice to be transmitted as it 'actually sounds' -- then a flat response curve from 300-3,000 Hz will be fine.
    Some operators desire emphasis or de-emphasis of the bass (low pitch) qualities or treble (high pitch) qualities of their voice. Some commercial radio announcers prefer specific microphone -- ask AG3Y about "voice talent".
    Poor selections are why some people on the radio sound more like Donald Duck or Darth Vader. :rolleyes:

    As far a DIY, as long as you can find a good sound quality foam and a baffle --
    you just need to properly fit those components (black panty hose can be used) with your new element

    Earlier QRZ Q&A dicussion of D-104 retro-fits

    Steven Fraasch, K0SF
    Adapting the Astatic D-104 Microphone for Use with Modern Transceivers
    August 1999 QST, page 34
    This article is available free for ARRL members

    Joe Carcia, NJ1Q
    More on the Astatic D-104
    March 2001 QST

    George Heidelman, K8RRH
    More on the Astatic D-104
    June 2002 QST

    W8CWE : D104 adapted for Icom 706

    D104 index -- "bookmark" in your browser

    Doug DeMaw, W1FB (sk) FET circuit for D104 - CQ February 1994
    (mentioned in web pages below)


    D104 and Icom equipment

    Last edited: Feb 13, 2009
  6. KJ5XX

    KJ5XX Ham Member QRZ Page


    Ahh, In Search of the Lost Chord - if memory serves me right (which it often doesn't these days :rolleyes: ) was the name of a Moody Blues album.

    Great information! Some of this I already have and some is new to me.

    I did FET/Op-amp conversion of a D-104 a few years ago based on a design by Walt Breining, N9WB. Works great and I use it as my current station mic. I love these old mics though, and restoring them is something that is within my rather limited electronics ability. :eek:

    I own several of them, including an old Astatic DN-20U (similar to the DN-HZ) that I'm restoring, with new hammartone finish, new felt, etc, and just thought I'd try a different approach and try to find a low Z (on the order of 600 ohms) element to replace the old Rochelle Salts crystal element in these mics, thereby eliminating the need for the op-amp circuit.

    The Kobitone crystal element mentioned in one of the posts may be the best answer, but thought there might be options in other mic element types.

    Haven't heard the black pantyhose trick. Will have to give that a try (gee honey, looks like you have a run in your stockings - what a shame!)

    Thanks again Greg for the good info.
  7. W2VW

    W2VW Ham Member QRZ Page

    The Kobitone elements have a lot less low end frequency response compared to a properly terminated, undamaged D-104 element. I have tried several into an MPF-102. Forget it unless you just want to bust pileups.


    Good information - thanks! Have you found one that you like?
  9. KJ5XX

    KJ5XX Ham Member QRZ Page


    Thanks, wasn't aware of that, and I'll ask the same question as above - is there a particular element that you prefer?

    The problem with finding an answer to a question like this isn't that there is no information to be found, it's that there is a LOT of information and not all of it agrees. But, after doing a bunch of reading on the subject (and many thanks to Greg and the other helpful posts here), I'm convinced that if modifying or restoring a D-104 for use with modern rig, there are several options:

    1. If the mic has the "amplified" base (T-UG8 or T-UG9), you should be able to use the mic without alteration - just wire it to match your particular radio.

    2. If the mic has the older, non-amplified (UG8) base, you can build a simple JFET circuit like this one

    3. Replace the old crystal (Rochelle Salts) Astatic element with the Kobitone 25LM022 (assuming the mic has the amplified base)

    4. Replace the element with a Medium-Z (~600 ohms) dynamic element such as the kit available from Heil ($70 US)

    Since the old crystal elements of these mics are sensitive to both heat and shock (such as if the mic was dropped) you may modify the mic only to find that you have poor audio quality. If this is the case, you can always revert to options 3 or 4 above.


    Last edited: Feb 13, 2009
  10. KA9VQF

    KA9VQF Ham Member QRZ Page

    At one point in my life I had a CB shop. I personally don’t like the D-104 mic but a lot of other people did.

    I converted a lot of them to dynamic mic elements as it was pretty much imposable to obtain elements from Astatic.

    I used a dynamic element that was readily available from Radio Shack at the time. It worked well with the little amplifier already in the base of most of the D-104 mic’s I worked on.

    I used plain old Styrofoam sheeting that came in packaging to fill the headshell. Once I had a round piece large enough to fill the mic shell, I just cut a hole in the center and glued the mic element to it with Elmer’s glue.

    I usually put a piece of thin red felt between the mesh of the front part of the mic and the element.

    You need to take care that none of your mounting material or if you use it felt {or even nylon stocking} is touching the front of the mic element. This can cause a muffling to occur.

    My idea was that by using the red felt people would be able to immediately recognize that it was no longer a stock D-104. Besides having the added benefit of masking ‘puff’s’ when the user would talk closely to the element, in my mind, it made the mic more attractive.

    I used a few electret condenser mics in D-104’s too. Usually for folks who really wanted a desk mic for their 2M rigs. Most mobile 2M radios already had a condenser mic in the original mic so it was pretty easy to wire one for it.

    Generally I would remove or disable the amp in the mic stand tho. It was not needed.
  11. K9STH

    K9STH Ham Member QRZ Page

    The part number, 25LM022, listed by XX is the Mouser part number. The Kobitone part number is KT-400023 but they do list the 25LM022 as a part number since Mouser sells a lot of those elements. It definitely is an excellent replacement for the original element which is no longer available from Astatic.

    The only thing is that the Kobitone element is smaller in diameter than the original element and you have to make something to hold the element in place. On the kits that I sell for the D-104 I cut a circle from styrofoam that fits the D-104 head and then cut another circle from the center of this foam to hold the cartridge. Then I use silicon adhesive to secure the cartridge to the insert. Works and sounds great.

    Mouser's price is now $4.77 in single quantities. That price is a "bit" higher than the under $3 that the cartridges were selling for about a year ago.

    To get a good fit of the styrofoam you either have to be VERY careful when cutting the circle or else use a hole saw the correct size. A large size hole saw is not that expensive but most people don't want to spend about $20 just to cut a single piece of styrofoam! Then there is the price of the smaller hole saw which matches the size of the element. Those run about $10 each.

    Glen, K9STH
  12. W2VW

    W2VW Ham Member QRZ Page

    This is another cockroach subject. It pops up here every few months. You can't kill it. The same people (including myself) post the same stuff. Someone always writes the crystal D-104 off as lousy based on experience with the popular amplified mic stands marketed to citizen's band folks.

    And they wonder why certain well known successful DXers don't post on QRZ.

    The following is based on actual first hand experience.

    I have tried the popular replacement Kobitone mics based on recommendations seen on the WWW. They fit easily in just about any old mic. I put a pair in one of those old Calrad pill microphones that is supposed to look like an RCA 77DX. Also in there is an MPF-102 impedance converter. I never use the mic because it sounds like a lightly damaged D-104 crystal. Very peaky in the upper midrange with a slight tin can sound. Low end response drops like a rock compared to the control mic D 10 Foar. Tried it again on the bench with another Kobitone and got the same results. Same circuit works fine with a D-104.

    If you are running an old Collins S-Line there will be no difference. Use a modern rig and the difference will be hard to ignore. I'm not talking about sounding like someone talking through an 8 foot length of 6" PVC pipe either.

    I tell all my friends that I'm always looking out for a GOOD D-104 element. I have one at work and one at home. I also have a 5 gallon bucket filled with drowned ones that came from an estate with a flooded basement. Also have several dozen from all over that I would not use on the air due to their unhealthy state. As a matter of fact, any of y'all out there want a few bux for your hopeless undamaged D-104 elements drop me an email. Address is good on.....QRZ.

    It's getting very difficult to find these in good shape. Many sound OK but few are really good.

    The original Astatic preamps which used bipolar transistors ruin the frequency response because they load the crystal's element. It must be terminated into a high impedance to work properly. That's why some people think those mics are hopeless. Hence the MPF-102 impedance converter.

    No, I don't like any other microphones by themselves. That is to say there are plenty of other great microphones but most need some kind of frequency shaping to work well with radio. The D-104 is absolutely the best microphone to use when there will be no fancy adjustment available for tone.
  13. W9GB

    W9GB Ham Member QRZ Page

    David -

    As you know, crystal microphones are made with Potassium Sodium Tartrater (Rochelle Salt) Crystals.
    Photo of a nice homemade crystal

    Unfortunately, Rochelle salts do NOT like Shock, Heat, Mositure or Abuse/'G' Shock (not friendly for environmental usage extremes) -- the crystalline structure of the salts breaks down under these conditions ... then the crystal element is dead. It's dead Jim!

    One approach is to take all of those bad crystal elements -- to make "new" ones (recrystalize) -
    no, not a Star Trek episode with Scotty reforming di-lithium crystals:rolleyes:

    How to prepare Rochelle salt from baking soda (sodium bicarbonate) [NaHCO3]
    and cream of tartar (potassium bitartrate) [KHC4H4O6]
    which are available from any grocery store.

    How to grow crystals

    An interesting DIY project.
    BTW, you can also make your own elecret element !

    Last edited: Feb 13, 2009
  14. W2VW

    W2VW Ham Member QRZ Page

    Thanks for the dope on rebuilding crystal elements OM. I'll put that on the list....
  15. K9STH

    K9STH Ham Member QRZ Page

    Like any microphone element the input impedance of the circuit being driven is definitely a factor. The Kobitone KT-400023 sounds fine, at least in my experience, and as good as, if not better than, the original Astatic crystal elements that I have heard. I do have one of the very last original D-104 elements that were shipped from Astatic and, when operated with any of my Collins, Heath, or Hammarlund transmitters the reports that I get when using the Kobitone cartridge are at least as good as and in many cases better than those with the original Astatic cartridge.

    The Kobitone cartridge is pretty flat up to a little over 1000 Hz and then has a rise up to around 4500 Hz and then drops off after that. In the 300 Hz to 3000 Hz range the response is pretty good. For the response chart go to

    and you can get a good idea of the frequency response of this particular cartridge.

    However, like any other cartridge, if you run it into the wrong impedance then you are definitely going to get a different frequency response that can vary all over the place. That is why one must be careful when they are "playing around with" different cartridges. Bob Heil doesn't manufacture cartridges. However, he has "discovered" which particular cartridge works best in different applications. For this knowledge he does get a premium price.

    Several years ago a group of amateur radio operators decided to obtain quite a number of different microphone cartridges, ranging from Radio Shack cartridges costing less than $2 to Heil's "top of the line", and hold a "blind test" by using all these various microphones "on the air". None of the cartridges were identified to the other stations other than a letter or number. The "on the air" reports were somewhat "eye opening". Most of the cartridges, including the "el cheapo" Radio Shack models got excellent audio reports that were as good as, and in some cases better than, Heil's "top of the line" cartridges. Now these were side by side comparisons. That is, several different microphones were used, one after the other, when in QSO with various stations.

    Unfortunately, to my knowledge, the operators who conducted the tests did not publish a list of just which cartridges worked better than others. All that I know of being issued was a relatively "blanket" statement about the general quality of microphone cartridges. Since many amateur radio operators do not want to "bother" with trying several different cartridges they usually purchase one of the Heil models that they know will usually work fine. As such, there is a trade-off between cost and having to experiment with different cartridges. That is, Heil has done the experimenting and furnishes those cartridges that he has found to be reliable. Of course, you do have to pay for this and that is proper.

    Again, each cartridge has an optimum impedance that it needs to "feed" and that does vary among the various radio designs. Usually the impedances are pretty close but there are enough variation that certain microphone cartridges work better for individual voice characteristics on different radios. Also, the characteristics of an individual's voice vary from the next person and the frequency response of a particular cartridge can favor one person's voice over the next person's voice. That is why some professional announcers carry their own microphone to be used by only them when broadcasting, recording, and so forth. They have "found" the "right" microphone that enhances their voice and that gives them an edge in their profession.

    Glen, K9STH
  16. KJ5XX

    KJ5XX Ham Member QRZ Page


    Good information - thanks for the tips!
  17. KA0GKT

    KA0GKT Ham Member QRZ Page

    Yep, it was 1n 1968. I remember my mother not liking the album cover too much...iirc the single released from that album was "Ride my See-Saw", but it wasn't the first recording to mention "The Lost Chord".

    Jimmy Durante recorded a little ditty in 1947 called "I'm the guy who found the lost chord".
    Last edited: Feb 15, 2009
  18. W2VW

    W2VW Ham Member QRZ Page

    Glenn, based on the graph in your link the Kobitone would make a real nice replacement for a D-104. The problem is that this graph isn't anything like the mic's response when followed by a FET inpedance converter.

    Impedance match should not be an issue here. That it taken care of by the FET.

    Taking a good look at the graph, I think it is completely bogus. It doesn't even show the low end corner frequency properly. Maybe marketing department people playing engineers.

    FYI here's an interesting comparison of several mics. This one looks like reality.
    Last edited: Feb 16, 2009
  19. K9STH

    K9STH Ham Member QRZ Page

    What I have found is that the design of the FET preamplifier has an effect on the frequency characteristics of the cartridge. Subtle changes in the values of the capacitors and resistors used in the design can vary the response all over the place.

    In the case of my particular D-104: I was given a "G" stand that had a defunct amplifier and therefore I started from "scratch" using some "accepted" designs for an FET amplifier. Using the published values for components the comments that I received from locals who knew what my voice "sounded like" in person commented that the audio definitely sounded "tinny". By "playing around" with various components I could change the characteristics from "tinny" to "bassy" with only minor changes in values. Finally, I was able to come up with characteristics that, according to others, most sounded like my actual voice. This effect was basically the same with both my original Astatic D-104 cartridge and with one of the Kobitone cartridges.

    Because I was using the microphone with various rigs I ended up installing a switch that allows me to choose from either a direct connection to the cartridge or through the preamplifier. My Collins S-Lines do not like the preamplifier whereas my Heath SB-Line equipment does like the preamplifier.

    My main microphone is not the D-104. I installed one of the Kobitone elements in an old Radio Shack ("Realistic" brand) microphone that is mounted on a "goose neck" that is attached to the first shelf on my main console. To switch among my various transmitters I used to use a switch but that proved problematic under certain conditions. So, I replaced the switch with a panel that has RCA jacks going to each individual transmitter/transceiver. To change the microphone I just plug a cable from the microphone itself into the appropriate jack. The PTT circuits still go through a switch.

    The audio reports that I get when operating on SSB (unsolicited) are excellent no matter if I am running one of my Collins S-Lines, any of my Heath SB-Line equipment, or my Hammarlund HX-50A (that I use on 160 meters). Now my voice is definitely not "bass", that is I do have some higher frequencies in it. At least for my voice patterns the Kobitone cartridge matches very well. However, I certainly can agree that for other voice characteristics other cartridges will provide a better match. That will be true for any microphone cartridge, depending on the characteristics of the particular individual's voice there will be certain cartridges that work better than others.

    It is possible to change the frequency response of most cartridges by "playing around with" component values in the audio chain. Of course, tailoring a particular station can involve some exacting work and, if the station is used by someone else, that tailoring can work to a disadvantage. Also, not every amateur radio operator has the ability and/or inclination to make the necessary changes. Therefore, the "easy way out" is to go with a microphone that is readily available that generally "sounds good".

    Glen, K9STH
  20. WD4DMZ

    WD4DMZ Ham Member QRZ Page

    This discussion was very helpful. Thanks!

    I am high school physics teacher and wanted to set up my old Kenwood TS530s in class for demonstrations of radio physics. I needed a mic but all that I had that was not in use was a D104 with a very poor cartridge.

    Based on this discussion I purchased the kobitone element (two actually) and replaced the original element with it. I used the thick felt from an old jewelry box to support it within the head and it works just great!

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