Electret Microphone Gain Adjustment Made Simple

The popular "electret" microphones of today are inexpensive and provide very good performance for just a few dollars. Often times they come with a fixed load resistor but I have discovered that by making that load resistor variable, the gain can be adjusted.
Below is a good description of condenser and electret microphones:
Condenser Microphones
Principle of Operation:
Condenser microphones operate on the principle of variable capacitance.
They consist of a thin diaphragm placed very close to a backplate. When sound waves hit the diaphragm, it moves, causing a change in the capacitance between the diaphragm and the backplate.
This change in capacitance is converted into an electrical signal.
Power Requirements:
Condenser microphones require an external power source, often referred to as phantom power (typically 48V) or a battery, to maintain the electrical charge between the diaphragm and the backplate.
The power source is necessary for both the capsule and the internal preamplifier.
Sensitivity and Sound Quality:
Condenser mics are known for their high sensitivity and excellent frequency response, making them ideal for capturing detailed and accurate sound.
They are often used in studio recordings for vocals, acoustic instruments, and other applications where sound quality is paramount.
Cost and Durability:
Generally, condenser microphones can be more expensive due to their complex construction and high-quality sound reproduction.
They are more delicate and less durable than dynamic microphones, requiring careful handling.
Electret Microphones
Principle of Operation:
Electret microphones are a type of condenser microphone but with a significant difference in how they are powered.
In electret mics, the diaphragm or backplate is permanently charged due to a material called an electret (a dielectric material with a quasi-permanent electric charge).
This eliminates the need for a continuous external power source to maintain the charge on the diaphragm and backplate.
Power Requirements:
While electret microphones do not require phantom power for the capsule, they still need a small amount of power (usually provided by a battery or a low-voltage power supply) for the internal preamplifier.
This makes them more convenient for portable applications.
Sensitivity and Sound Quality:
Electret microphones are also quite sensitive and have a good frequency response, though they are typically not as high-end as true condenser microphones.
They are widely used in applications where space and power constraints are important, such as in lavalier (lapel) mics, headset mics, and various consumer electronics.
Cost and Durability:
Electret microphones are generally less expensive than true condenser microphones.
They are durable and can be made very compact, making them ideal for use in portable and consumer devices.
Summary
Condenser Microphones: High sensitivity and excellent sound quality, require external power (phantom power or battery), often used in professional audio settings, and are typically more expensive and delicate.
Electret Microphones: A subset of condenser microphones with a permanently charged element, require less power, commonly used in portable and consumer applications, more affordable, and durable.
Both types of microphones have their specific uses and advantages, making them suitable for different audio recording scenarios.

[@ElPasoTubeAmps]

I made a couple of "word mistakes". One is if you make the series capacitor a low value say, 0.001 uF you might be able to tailor the output frequency response and attenuate the lows and not the highs. I would think if you use a 10uF capacitor it should be "non-polarized" but the ones we get off Ebay use polarized (standard) electrolytic capacitors. Seems to be OK.

[@JaySteiner]

Thank you for making this video! Ive been making an interface between my radio and a headset that uses an electret mic. The original design called for a 1K resistor but the gain was really low. By mistake I put in 2.2K when I was tinkering and to my surprise the gain increased. That had me scratching my head. Now I finally understand why!

[@aldo9887]

Hello, El Paso.- Very good for the electr. Mike.- For You, much Greetings from Verona city, Italy.- Thanks for All .- Excuse me for the poor English Language ! p.s. : Ciao by Aldo.-

[@apexmcboob5161]

And Merry Christmas and a Happy New Year to you and your family from Canada.

[@johnnorton6085]

Good information to know. Merry Christmas and Happy New Year.

[@tonygustafsson8550]

Merry christmas and a happy new year to you and yours, from sweden.

[@jdmccorful]

Nice, thanks for the tip. The best to you and yours.

[@jeanreprendraibien9126]

73. Congratulations for this démo very cool and interesant. Where and how connect a vu meter to control the gain effect? Just before the out? Thanks

[@ElPasoTubeAmps]

I haven't thought about the VU meter but I would think the impedance would be too low and load down the output of the microphone - I have never tried it - but I would suspect a VU meter would need to be located further down the audio chain. I adjust the gain and watch the RF power output of the amplifier to the antenna with a peak reading meter. I personally like the LED peak reading meters better than the Bird 43 style. I guess I just like the blinking lights 🙂 73 WA4QGA

[@fullwaverecked]

Always great videos and info El Paso. Thanks!

[@ElPasoTubeAmps]

At 2:56 in the video, I say attenuate the highs but mean attenuate the lows...

[@SKYHAWK0115]

Enjoyed the video on your electret microphone. Also, could you show us the electret condensor mic itself before the install ? I would like to see the gain of the electret microphone in action along with the quality of performance. That is, your gain on the watt meter and modulation as you turn up or turn down the new inline potentiometer. To me that would be a better example of gain from your schematic. Could you possibly update the video on this project ? Thanks Billy Albq. N.M.

[@ElPasoTubeAmps]

Hi Billy, I don't think a YT video can be updated after posting. We used to be able to add comments to the video in case we said something incorrect but YT notified us and stopped that because they said the comments could not be seen on hand-held devices and most people apparently, watch YT on their phones instead of a PC. I think your suggestions are very good and if I make another video about microphones I will show the mics and how modulation is controlled by the inline pot. Here is one type I have used from Ebay. www.ebay.com/itm/354402889211?hash=item52840eedfb:g:LU0AAOSwd0BVtQn0&amdata=enc%3AAQAHAAAAoHDeTqjNAjk9ffBpDFfy8qi53kDjWWP6bhht4t6iouBe7LXzK5nBPeoQ7ynwsHpUX2lnJby1p0wEXY4P9R%2B8OG2if%2FY6op7%2BtJLvGrDe91tNhIsUsuHBAaXgKo0GQsLtt61KyblRCNnw7Ccr%2F5GbhLiWnrGYEIYRkLC6tHeHI20znmjma6W3b16V60PvY5vSYBbczEsu2cSM9E821%2BjDmm0%3D%7Ctkp%3ABk9SR8irhb24YQ Here are the 69 cent mic elements I have gotten from Amazon - now they are only 59 cents... but you have to buy 10. www.amazon.com/Cylewet-Cylindrical-Electret-Condenser-Microphone/dp/B01N0VMN9P/ref=sr_1_9?crid=2LMX5TJ9DY3HF&keywords=condenser+mic+element&qid=1674027597&sprefix=condenseer+mic+eleme%2Caps%2C111&sr=8-9

[@owenvinall9970]

Thanks for your excellent video. I have a Ubitx Hf kit rig. Have been battling low rf output on voice for some time due I believe to low output from my FET Mike. I will be trying your suggestions out as soon as I can. Owen Vk5kov from down under of course.

[@ElPasoTubeAmps]

Hi Owen, I hope a mic upgrade works for you. I know the original D-104 elements when they get weak will hardly modulate my transmitter, I think mostly because they have lost their low frequency response. 73 WA4QGA

[@SignalSmoker]

great video. instead of a build-it-yourself, i sent out for a electret microphone amp board already pre-made. . i want to add a volume pot at the audio out but not sure how many ohm pot to get. it has 1 ic, 2 transistors and operates from 5vdc to 12vdc. any ideas? thank you.

[@ElPasoTubeAmps]

To make a zero to full volume output control, you connect the output of your mic amp board to one of the pot and the other end of the pot to ground. The variable signal is then taken off the center pin of the pot and the ground end. Depending on which end you put the signal in and the end you ground will determine if the volume goes up or down when you turn it CW/CCW. Electret-condenser mic elements are fairly low impedance devices so any pot between 2.5K and 10K should work fine. I would likely go with the higher values like 10K. Hope this helps.

[@SignalSmoker]

@@ElPasoTubeAmps thank you so much for your help. i am trying to keep the costs down and dont want to buy a pile of assorted pots. i will start with a 10k and update results here.( may take awhile...)

[@SignalSmoker]

hello again! so i have everything hooked up accordingly, and the issue is that its too loud. the "pot" on the board is counterclock all the way- not sure if it even works. i have it running thru 2 pots which i scavenged, both 50 ohm and hooked in a sries circuit. and i cant control the vol. so i sorted some various resistors to put in-line including a 1.5 mega ohm, still too loud. thoughts? thanks!

[@ElPasoTubeAmps]

I don't know but maybe you have the input pot connected wrong ? The input from the, for example, RCA input jack goes to one side of the volume control the other side goes to ground and the wiper goes to the input grid of the first stage. The value of the pot should be something betweel 100,000 and 1 megohm. Also, although it does not have to be, a volume control should be a logrithmic type pot and not a linear pot. Our ear responds logrithmic rather than in a linear manner. Either will work but the linear pot will get loud quickly whereas the log pot will not. Putting a resistor in series, even 1.5 meg is not going to do anything significant as the current flowing thru is in the microamps so there is no voltage dropped across the series resistor. Hope this helps.

[@SignalSmoker]

thanks for your quick response!! the amp in question (if you care to look) "DC 5V-12V LM386 electret microphone power amplifier board" in the walmart search, it shows the 2 transistor board with input for electret mike. i dont have a pot in that circuit, just wired direct. the pots i used are both for the audio out. i will look to the logrithmic pots and see what i can find, not familiar with those. thanks again!

[@home_Grown_studio]

No man, following to the letter all i got was a great deal of noise, it improved slightly removing the 2.2k and just using the variable. even that was nothing to brag about

[@ElPasoTubeAmps]

That's not good... Are you using this microphone on new equipment like iCom, for example, or vintage equipment like vacuum tube Collins equipment?

[@home_Grown_studio]

@@ElPasoTubeAmps I am using it as an external Mic for a Sony Digital voice recorder. ( Model: ICD-PX312 ) I am making a Mic array using a NE5532 TDA1308 Mono Audio Signal Input Mixing Board

[@ElPasoTubeAmps]

@@home_Grown_studio One of the things that I have found that surprises me with these little mic elements, is they work very well into a high-Z input like vacuum tube circuits. Input Z is around 1 megohm. I have also tried to use them on modern solid state devices like iCom radios and they don't work so well. The input Z of the iCom type radios is a low Z impedance - not exactly sure what it is but I believe in the K ohm range. I bet your Sony device is a low Z input. Not sure how to help at this point.

[@home_Grown_studio]

@@ElPasoTubeAmps Actually I am getting close to achieving my goal. Been playing around with resisters getting better. Before I make the connections to the mixer I just want a good sound with little noise as possible. Anyway, Thx for the posts they are appreciated

[@gerhardvanwykzs4rum685]

​@@ElPasoTubeAmps600 ohms for newer radios