Transistor Radios and D-104 Microphones (2024)

"Editor's Note: Due to the popularity of some of eHam's older articles, many of which you may not have read, the team has decided to rerun some of the best articles that we have received since eHam's inception. These articles will be reprinted to add to the quality of eHam's content and in a show of appreciation to the authors of these articles." This article was originally published on: 3/12/2011

How to get good audio characteristicsfrom an old Astatic D-104 on a modern transistorized rig.

Transistor Radios and D-104 Microphones (1)

Experimenting with different peripheralham radio equipment has opened the door to a lot of education. In thelearning process it has been found that some older equipment is notcompatible with newer gear. One of the things we always strive forwhen using voice modes is keeping the audio ineligible and nottedious for others to listen to.

The old classic Astatic D-104microphones were great sounding mics on the old boat anchor tube-typerigs. This was because the impedance of the D-104 head is in theorder of several thousand ohms. The responsiveness of the tube typeaudio input circuits facilitated a great impedance match to theD-104. However, in the newer transistorized rigs, these audio inputcircuits leave the D-104 sounding very "tinny", at best.It's not because the crystal type element of the D-104 doesn't havethe ability to "hear" any low end in the human voicecharacteristics. It is directly a result of impedance mis-matchesbetween the microphone element and the radio's audio input circuitry.

For example, here is a short list oflow end roll-off stats for the input of audio circuits when using aD-104 microphone element:

100 k = roll-off @ 500 Hz
500 k = roll-off @ 250 Hz
1 meg = roll-off @ 100 Hz
4 meg = roll-off @ 30 Hz

Information was sent to me from a goodfriend, Joe ( K2PSI ). Along with a couple dollars worth of parts theschematic was sent with the preceding roll-off statistics. I havereworked the schematic drawing for placement in this article. So, itwill be easier to read.

Transistor Radios and D-104 Microphones (2)

The way this works is a field effecttransistor (FET) p.n. MPF 102 is placed in a common sourceconfiguration. The D-104 cartridge sees a 2.7 megohm load impedance.The 1 k source resistor provides the proper load impedance to the rigwith transistor audio input parameters. The 1 mH and 100 pF capacitorcombos are used to filter any RF that may be picked up by the D-104element or interconnecting wires. The voltage required to power theFET is supplied at the VDC pin of many modern rig's mic connector. (avoltage anywhere between 4 and 14 volts +DC works well) If your rigdoes not have a voltage out pin on the mic connector, a nine voltbattery can be used.

This circuit works very well with theTen Tec Jupiter, here in the N8NSN shack. Certainly othertransistorized rigs may benefit from this circuit in combination witha D-104. An old defunct jewelers magnifying lamp served very well asa boom for the mic head. The cavity which once housed the transformerfor the fluorescent circular tube, now provides the perfect place forthe home brew circuit board of the D-104 requirements.

Transistor Radios and D-104 Microphones (3)
Transistor Radios and D-104 Microphones (4)

This is the circuit inside thetransformer cavity of the old defunct jewelers lamp. As you see thecircuit could easily fit in the base of a D-104's T-UP-9 stand base.Here, the circuit board was drawn, cut, and mounted on a couple of3/4 inch metal stand offs. This also provides the means ofshield/ground for the entire apparatus. The circuit is small enoughthat it can be mounted on bread board, wrapped in some kind ofinsulator and stuffed in any available containment unit.

Transistor Radios and D-104 Microphones (5)

There you have it... The old D-104 isback in the line up. Fabricating the means you choose, should youdecide to try this, for making the old D-104 a part of the modernshack - how to connect it in a convenient operating positionand such - will be left to you. The photos here were providedas a means of size comparison. The defunct jewelers lamp was only amatter of convenience coupled with a desire to not have any deskmicrophones lingering around on the desk. My hope is that we allcontinue to grow in the amateur radio service. There is something foreveryone from the plug and play operators, experimenters, builders,to the design and fabricate types. The main thing is... HAVE FUN !

Here is a recap on all the parts youneed to build this awesome little circuit:

3) each of 1 mH inductors
3) each of 100 pF
2) each of .01 uF
1) each of 2.7 megohm
1) each of 1 k ohm
1) each of 220 ohm
1) each of 1000 uF @ 15 V
1) each of MPF 102 FET

The 13 parts, some sort of circuitboard, a dab of solder, and a whole lot of fun.

Transistor Radios and D-104 Microphones (2024)


What is the history of the D104 microphone? ›

Introduced in 1933, the Astatic model D-104 became known for its high frequency response that contributed to better communications audio quality. Early D-104 mikes used a 1" thick case, a large ID tag, and holes for "ring & spring" mounts. The design was modified in April 1937 with smaller tags and reduced thickness.

What is the impedance of the D104 mic? ›

The D104 has an impedance of 500k to 4.7 meg-ohms. Most Vintage transmitters require these high impedance microphones to operate properly. In turn the D104 also likes to see a high impedance. Below you will find a few interesting Links and articles on the D104.

What is the frequency response of astatic D104? ›

The end result is a very flat frequency response with 1.5 dB rolloffs at 20 Hz and 45kHz. In other words, you'll hear exactly what your D-104 really sounds like. This circuit draws 0.5 mA at 9VDC. A power switch (not shown) can be used to turn off the circuit when not used.

How do you use a radio mic? ›

How To Use Radio Mics ?
  1. Turn on the transmitter: The transmitter is the part of the radio mic that you hold or clip onto your clothing. ...
  2. Set the frequency: Most radio mics have a frequency selector switch or button. ...
  3. Turn on the receiver: The receiver is the part of the radio mic that connects to your sound system.

What is the oldest microphone? ›

The microphone was initially introduced in 1877 by Emile Berliner who had been working with Thomas Edison. It was a drum-like device that consisted of a carbon button microphone. During this time, many other models of microphone were being used but the carbon button microphone was the one that was generally accepted.

When did radio microphones come out? ›

Shure Brothers claims that its "Vagabond" system from 1953 was the first "wireless microphone system for performers." Its field of coverage was a circle of "approximately 700 square feet", which corresponds to a line-of-sight distance of only 15 feet (4.6 m) from the receiver.

What is the best microphone impedance? ›

Therefore, you would want to make sure you are using a mic with an output impedance rated below 1200 Ω. Please check the impedance ratings for your interface and your mic before making any purchase. If the impedance for the mic is higher than for the input, a loss of signal strength will occur.

How many ohms should a microphone have? ›

One important characteristic of a microphone is its output impedance. This is a measurement of the AC resistance looking back into the microphone. Generally, microphones can be divided into low (50–1,000 ohms), medium (5,000–15,000 ohms) and high (20,000+ ohms) impedance.

What is the difference between high impedance and low impedance microphones? ›

A high impedance microphone or guitar will usually output a greater signal (voltage) than a low impedance microphone. This high impedance signal works fine and even has some advantages in a sound system as the mixer or amplifier doesn't need to boost the signal as much.

What is 20kHz frequency response? ›

Our hearing ranges from very low frequencies, starting at 20 Hz, to very high frequencies at around 20 kHz (20,000 Hertz), though an individual's hearing will fall between these two extremes. In a musical sense, we often see this split into bass, middle, and treble sections.

What is frequency response technique? ›

What Is a Frequency Response? A frequency response describes the steady-state response of a system to sinusoidal inputs of varying frequencies and lets control engineers analyze and design control systems in the frequency domain.

What is frequency response Hz? ›

Every sound has a frequency range, measured in hertz, which is the number of sound waves that pass in each second. Audio equipment like amplifiers, digital to analog converters (DAC), headphones, and speakers have to reproduce these frequencies, and their ability to do so is described as frequency response.

What radio mic frequencies can I use? ›

173.7MHz to 175.1MHz – VHF, you'll typically be able to use 3 frequencies together, the transmitter power is limited to 10mW (or up to 50mW on body worn packs) 863MHz to 865MHz (Channel 70) – Within this range you'll be able to use 4 frequencies and transmitter power is limited to 10mW (50mW on belt pack transmitters)

Can microphones pick up radio waves? ›

A less familiar source of microphone interference is radio frequency. Radio frequencies are way outside the range of human hearing, but a microphone's electronics can inadvertently convert an RF signal into an audio-band signal.

How to fit a radio mic? ›

The best position is to run the microphone cable up the back of the neck and through the hair, with the end of the microphone just sticking out of the hair line, either in the centre of the forehead or above one of the eyes, again with the microphone head just in front of the hair line.

What is the history of Soyuz microphones? ›

The History And Manufacturing Of Soyuz Microphones

Soyuz Microphones was founded in 2013 by American musician David Arthur Brown and Russian businessman Pavel Bazdyrev. The microphone company's philosophy is based on the unison of Russian engineering and Western design.

What is the history of the U47 mic? ›

It is one of the most famous studio microphones and was Neumann's first microphone after the Second World War. The original series, manufactured by Georg Neumann GmbH between 1949 and 1965, employed a tube design; early U 47s used the M 7 capsule, then replaced by the K 47 from 1958.

What is the history of the RCA microphone? ›

RCA's first ribbon microphone was manufactured in 1931, impacting both the audio recording and broadcast industries in the United States and the world. A year later, the first of the RCA 44 series ribbon microphones was released. The 44 quickly gained a reputation as the most musical sounding microphone ever made.

What is the history of crystal microphone? ›

Piezoelectric Microphones, also called Crystal Microphones, were used primarily between 1930 and 1960. At the time, these were important to the home recording and small-scale paging market, but were later replaced by lower-cost dynamic and electret capacitor microphones.

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