Call sign: K5jxhSubject: Microphone modifications: Mods.
Microphone Madness, I will call this device a MIC , for short.
In the true spirit of HAM radio, we love to experiment. ( not only is this FUN, but we learn every day)
There are vast numbers of microphone types. (near endless) but we can reduce that list to a set of base technology, and I will avoid acoustics, mostly for now.
We don't run 100 ft stage, mic cables, ever. It's just inches here. (no chances of line loss (rcl), noise pickup, etc, but is shielded well and RF shielded too.)
It's not about efficiency, it's about proper levels and signal quality and low noise.
A dynamic Mic is just a very tiny speaker, an electromagnetic transducer is what it is, with very small mass and very responsive to your voice. (Hook up weak audio to the mic and it is now a speaker)
In fact, some old intercom's used a 45ohm speaker as the mic. (a pro dynamic mic is a very sensitive and sound compliant speaker, take one apart and see that)
Low Z Mics many at 200 to 600 ohms (this is at audio ac signal rates, this 600ohm its not DC ohms"DCR") & were used on all old tube gear, using a very high gain tube to amplify the very very weak Low Z mic signal.
Low Z Mics have weak outputs due to the low turns of wire on the bobbin, better mic's use very small expensive wire, that has many turns and this causes Mr. Faraday's laws to make more voltage for same shaking diaphragm.
High Z mics have a more expensive bobbin with huge numbers of turns, keep in mind the goal is the moving parts be super light weight (mass) to sound good , one can have a moving coil or a moving magnet. (and sounds different)
A ribbon dynamic mic has moving ribbon that is super compliant to sound pressure waves. (its forte) (a super nice mike with local amp, try one for fun !)
How are levels determined?, there is one answer: Mr. F.
Here is Faraday induction equation, E is volts (called EMF) see how N is multiplied times the other factor on the right? bingo more volts. dt is speed (dt = delta time) the funny d(phi)B is flux density.
One can say , volts out is equal to turns of wire times, (flux density ) divided by speed of said flux.
or more simply: " Epsilon(EMF) = Delta Phi / Delta t " (delta means "change in") Change in time, or density. (keep in mind here, that delta T, , gets smaller for faster speeds. (time is shorter and smaller , faster)
All generators use the same law. Spin it faster and more output power, or use stronger magnets or more wire turns; same.. (as a boy scout we made this from scratch; a toy generator ,then turned it in to a motor)
end math /physics...
Your voice frequency, Pitch, is speed, the flux density is fixed by that magnet inside (a core magnet) and wire turns varies by if mic is lowZ or High Z. (cheap mic, expensive mic, mostly)
That is why Whistling is so loud. (high pitch, and very fast, mic diaphragm movements results in higher signals.
One can appreciate that very super fine copper wire is very expensive and hard (snaps easy) to wind onto a voice coil bobbin and not break it, and is more expensive to make. (for many reasons, mostly physical reasons)
In addition to that, a stronger signal arrives at the AMP and has a far better signal to noise ratio as a door prize. (look ma. no 60hz hum ,that is EVERYWHERE)
In fact the High Z mic signal can travel (coax cable?) a long way , not ever needing an amp or a matching transformer to up the signals.
There is also a Ribbon mic, studio type, and is a super weak output super crazy low Z mic that takes a special amp to use. (or a built in step up transformer inside or outside as the case may be..)
Btw: by the way, the SB104 is a HIGH Z rig.
The Active mic's are all using some type of Amp, an Amplifier.
The most common today are the ELECTRET condenser mic with super will hidden FET transistor inside, FETS can have huge gain factors, called Hfe or Beta, and work best.
The signals out are very strong and super easy to use, and the most easy to send signal long distances down cables. (and avoid noise pickup) aka. noise ratio.
The reason we use ELECTRET's are many, it sounds good, levels are high, and it's only $1 to buy just one.
That is correct. the best mic is $1 (no, SUPER GOOD)!
We don't have HF Ham bands for broadcasting high fidelity, signals. sure... but...
In this case it's SSB and 3khz max. modulation bandwidth (but that includes harmonics and means a good mic sounds better!)
Not with standing, there are lots of tricks and tuning steps of any mic, to get a good sound under all conditions, even wind noise, or background noise, even screaming kids in the next room has solutions ! (besides , pulling the belt...and...)
Even the density of the foam used below can change the quality of sound.
Have fun tuning your mic !
Active mics (not passive):
The Electret mic (I use CUI elements in all mine for $1) are all ACTIVE mics, by its very nature it has condenser (capacitor) and FET inside, and needs power, to run it 1 to 10vdc and HAMS call it phantom power, but is just power no spooks here.
The data sheet is here.
Some radios have a 8v pin on the mic connector , never short this pin out. (or other raw unprotected DC power)
Phantom power is better, because if you ground the phantom line, no damage happens and we all know mic cords never short, right? (rhetorical)
Something like this, the device is 9.7mm in diameter, (in imperial gringo linear measure, that is 0.38" inches) by CUI part number ,CMA-6542TF-K, I warp it in foam and stuff it in the shell. (kids play really) My MD-1 below.
Some scalpers on fleabay sells this element (same P/N) for $50 wow ! It's $1 at mouser or Digikey.com. really.
The below photo on the right the dynamic element was removed, and then new element added, Any soft foam works here. The other foam side is a hole for the element, fully exposed to the front. (razor blade cuts, here)
See the soldered wire below, and than heat shrink tube used? If in a artful mood one can cut the foam round, but there is no need.
The technology is here:
Note the words, pre-charged Capacitor here... the FET amplifies this effect. The Wiki covers all this...
Photo 1: (upgrade elements) see the word capacitor here, it is. and was called long ago, a condensor mic. for the same reason. (the amazing part is the super level of integration here, and the great results)
Photo2: (MD-1) the black wire goes to Terminal 2.
If you have an real AMP in the MIC shell or base, then that AMP sets the level rules for output , not the the mic, element side (same person rag chewing). (the amp is a thing called the buffer and it sets output levels totally)
If the mic or amp changes the voltage to the element , then that too, changes levels. (some mics, have volume (gain) control)
The Electric mic is powerful and has a flat beautiful audio frequency response and is very sensitive (-40db for mine), and in most cases the best of the best. (as seen on TV mics. endless, (lapel mic's) and cell phones zillions.
You can change the MIC.'s tone and sound quality 2 ways, electronic RC filters, or mechanically.
To sounding like talking in a barrel? or like the sound of 2 tin cans on a string? (low bass or only high freq. vocals)
It is your choice how to do that, but I recommend using the natural Electret sounds, unabridged (&linear)first and if not happy just add a filter. (some mics for desk have a tone switch with simple RC filter ,like mine HAD)
I like the MD-1 (Yaesu) it has a real cast metal body and is greatly shielded from RF/ noise/ etc. I only want metal body mics. Plastic is a pain and needs super careful wire shielding and grounds.
The MD1 is quality unlike most, I like it, but not it's passive low Z element. (mushy sounding "like Godfather with cotton balls in mouth") Nor is its 600 ohms Z, it's worse 200 ohm impedance is no good, nor its weak levels.
My Yaesu MD-1 is shown below. (the story on mine)
I removed my stock element and wired in this CUI element for $1 . Wow. Now the MD1 sounds as good as my new ICOM mic. (it too has a nice factory ICOM electret mic)
My Icom 7200 uses 1200 ohms pullup to 8vdc, regulated.
Don't let $1 cost fool you, cost does not matter, spend money on the shell or base, and shielding is better on top brands, Some fleabay sellers ,sell junk raw bare plastic mics, that are $2 to make in china and sell for $150. ( avoid them)
Buy a quality body, then retrofit it . (I turn off the TV and retrofit it, in about 2 TV commercials it's done, wow)
Acoustics: (my weak topic, I'm an electronic tech)
The mic has 2 uses , in doors, and outdoors, the latter is subject to wind and background noise.
One can block the mic barrel side ports, forcing unidirectional mode and/or can put on a wind sock (buy one it's cheap) or inside mic add foam to make you happy.
There are even more MIC.'s , study unidirectional mic's or velocity mics and also background noise canceling mics. (for field work) or GUN MIC.'s.
Read up , learn the choices, or just use the ELECTRET, and be happy. (most are)
A mic can be setup that is super directional. Just like a beam antenna.
Last testing your mic.:
Use 2 radios, one person transmits to your rig 1 RF dummy load, and person two (or you) listens on receiver rig# 2. and test to your hearts content. (experiment , lots)
DETAILS of mine: "C8"
The 600 ohm MD1 is weak and my 200 ohm wonder, is 3 times worse, (and bad sounding) on new rigs, due to its very low output. (the old element has screw on the bottom holding it in place, I got rid of all that.
Leaving just 2 wires there. White and black.
The B8 version has a impedance transformer and high Z mod., but I have the C8 with the horrible 200 ohm mic and tone coil, that will short out my phantom power, so I cut the red wire at TONE coil.
The below drawing shows all steps I took and mods. The B8 model would need the switch kept on 50k ohms or the transformer cut loose. (wires) or the phantom will be killed.
Note the really flat response curve below, now. I have totally deactivated the C8 1,2,3 Tone control, inductor device. (cut red wire or the coil kills the phantom bias dead)
I did the mods, using the following methods, the mic, just 1 part change, the base, 1 red wire cut , add one resistor, and the coil cord ends are many changes, due to my hating, channel switches. (buy a spare cord and hack away?)
I tried to get all things done to fit on one page, below:
Schematic 1: The element terminal 2, is ground (black wire) it must be wired this way or the element will be DEAD. CUI # CMA-6542TF-K seen below. See hash marks? that be ground.
The blue voltages are my SB104 and 4.7k to 11vdc supply.
My SB104 was wired to run 11vdc phantom power to pin 1 via 4.7K resistor. The white wire must go to element terminal 1, and terminal 2 is ground black.
The output of any Electret element can be increased just by raising voltage to the element, we do that by changing the mic resistors. (ratios) This is not necessary ever I now think. It's super hot now.
My element runs 2v to 10v range,one could put a pot on the bottom for 2 to 10v range, easy. making the mic perfect for any radio made.
The resistor size , sets the voltage to the CUI element and the more voltage the more powerful is the output , this is because the FET transistor, does that. 1 to 2vdc is best.
The radios, phantom resistor sets the other factor for signal out. (they add up to total element current) In my case its, 5k +27k ohm and 11volts 5in radio, 27k in mic.
The spec calls out. "1.5 V dc (standard), 10 V dc (max.)" The recommend 1.5v at the element, but can work in a wide range. As bias voltage rises so does the drain pin on the FET and so does audio signal out rise..
Click here to see the Hi/Low Z version of MD1, it has a step up transformer inside.
Most the good old used mics are sold for $50 now or less, in real fleamarkets.
They are popular due to metal construction (shielded) lasting endless quality , and not over priced at $300 for plastic new mics.
This is the stock element I removed. (this is the LOWer Z version and can be seen with that very tiny and cheap coil ) Yaesu, it is. MD1, C8
Photo 3: (I could not resist characterizing it) This really is a super dog element. Might work on screaming banchee's ?"load and shrill"
DATA: This coil above is 33mH on my LCR bridge , so at 1000Hz, that is 207ohms, XL , it's not 600 like the others. The DCR is 16 ohms, so Z = 200 too.
Inductive Reactance (Xl) = 2 * Pi * F * L (* means times) F = 1khz