Introduction: Pre-amp to Electret Mic!

Picture of Pre-amp to Electret Mic!

This circuit is very easy to do!
and all parts of it are easy to find!
It is nice to put together with design of Rtty21
"The easy transmitter am"
so you can talk on the radio or put somewhere
hear the conversations of others!
the parts you'll need for this project will be!
Q1 = 2N3904
R1 = 10k
R2 = 100k
R3 = 10k
C1 = 0.1μf or if you prefer 104 or 100n
C2 = 0.1μf or if you prefer 104 or 100n
MIC1 = a common electret microphone
to put it together to design rtty21
and just put the place marked as output to next stage
pin 4 for the 555 (ne555/lm555/7555/ka555)
and ready to feed it to the same source of another circuit!
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tonya151 (author)2017-11-04

I made this circuit and was able to record some good audio connecting it to my systems's mic port, however there's this background noise that get's very prominent when I use a 9V source, with a 5V source it seemed somewhat eliminated.

How can I remove noise?

kubiX98 made it! (author)2017-06-27

Quick, easy and good project. Sound is litlle bit flat (mayby it's my mic) but pre-amp has strong gain. I can hear small noise but it's good enough to chat and gaming. Cost? 0,74$ for mic :D

mamachawngthuv (author)2016-07-14

Can i use 2n222 transistor for this circuit

doski90z made it! (author)2016-07-10

I've made it and it working but i have to things to share and ask

My sittings :

I connected the circuit to an atx power supply regulated (through lm317) to 4.5v and thin the output is connected to an AUX of my setreo.

1-Problem is i am hearing a buzzing sound , why? And how do i reduce or eliminate it?

2- the mic isn't very sensitive, any ideas to improve it??

michel moltrum made it! (author)2016-04-19

check this casing hehe...

lukas_tek (author)michel moltrum2016-05-26

Wow.It's awesome,I really like it.

KingBeauregard made it! (author)2016-04-14

This is pretty darn brilliant. As near as I can tell, the circuit finds its own point of stability, by self-correcting until the current through the base opens up the transistor exactly the right amount to be stable. (In other words, where V(ce) = V(b) + I(2)R(2), with V(b) as 0.7V.)

This circuit inspired me to finally, FINALLY build a common-emitter amplifier that seems to work to my satisfaction (see image). The electret microphone that it's connected to "idles" at about 4.5 V, and so does the transistor. It picks up sound well, oh and the transistor doesn't overheat and then go "poof" like with some of my previous attempts. :-) I don't know that this circuit is any better than the one lukas_tek gave us; mine's more complicated and you may find it doesn't work as well (YMMV). Nevertheless, it's an example of a standard common-emitter amplifier that works and is made of parts with pretty conventional values.

lukas_tek (author)KingBeauregard2016-05-26

Really cool,I will try it later.

michel moltrum made it! (author)2016-04-18

works fine, thank you!

KingBeauregard (author)2016-04-15

So I've been fiddling with the featured circuit more, to see if I could control the circuit characteristics more precisely. In particular, I wanted a circuit that "idles" with a V(ce) of 4.5V (since I'm powering it with a 9V battery) and I want 20 mA going across R3. I also want the output from the microphone to center on 4.5V. Using datasheets, Kirchoff's Laws, arithmetic, and a little trial and error, I've come up with these recommendations:

R1 - 18k (this could vary depending on your electret microphone)

R2 - 68k

R3 - 220 ohm

This makes for a satisfyingly sensitive microphone, and the electrical characteristics are about where I want them to be. I could probably rejigger this so that it runs on less current, but then I'd also have to figure out new R2 and R3 values (since, for what I understand to be best performance (which you supposedly get when Vce is half of Vcc), the current is going to determine R3 and therefore R2).

... you know, a smarter person than me wouldn't have spent so much time trying to work with data sheets and algebra and so forth. It's two simple steps:

1) Once you've decided on the current you want at Q, that tells you what R3 needs to be: it's Vcc divided by current, divided by 2 (because the intention is for the drop across R3 to be half of Vcc, and the other half will be across the transistor).

2) How to figure out what R2 needs to be to keep the transistor at half of Vcc? Just hook up a potentiometer, and adjust it until the voltage across the transistor is indeed half of Vcc. Then measure the resistance on the potentiometer.

When I just did this, I ended up with 72k; pretty close to what I got via much more complicated means earlier. Except using the potentiometer it took me less than five seconds.

For R2 and R3, values of 470k and 1k seem to work pretty well too.

KevinW93 (author)2016-01-14

Is the output considered "line level" ?

mamundsen (author)2012-12-22

This is sweet. I bought some super cheap electret mikes recently, and this is the third preamp I've tried to build. It's also the only one that works well. (I got a very nice progression from the first circuit as not working at all, to the second one working poorly and now this one working satisfactorily.

lukas_tek (author)mamundsen2015-11-27

Keep improving your skills!

MadGuitarist (author)2013-03-17

hey lucas can this preamp be used for normal mobile audio

lukas_tek (author)MadGuitarist2015-11-27

What do you want to do with it?

CameronF (author)2014-08-07


I attached this to my ipod amplifier, wired it to a speaker, and now peacefully listen to the outdoors from my basement.

Really good for your first instructable!

lukas_tek (author)CameronF2015-11-27


peter14 (author)2015-07-05

can I connect the output to my pc ?? I mean when I talk can I hear my voice to the speaker connected to my pc coz I want to build it and record

Robbie McVean (author)2015-06-17

YashK6 (author)2015-06-08

how can i connect this to a speaker?

RobinB1 (author)2015-04-06

At this point, if i connect it to a set of powered PC spekers or something similar via a 3.5mm jack, will It be aubible ?

MustafaH3 (author)RobinB12015-04-26

Yes, the amp in your sound card will take care of it.

ElleK1 (author)2015-02-24

Hi, I'm looking to amplify the voltage from an electret mic in order to make a VU meter- do you know whether this circuit would do the trick? If so, do you have any idea of the voltage gain on this pre-amp?

Any help would be much appreciated! ^-^

jowarkz (author)2015-02-08

good day . I need help , what to do to make an electret mic more sensitive?

Im making a clap switch using a bc547 transistor . I connected the negative pin of the mic directly to the base of transisitor , I observed that its not that sensitive . what should I do to make it more sensitive? please help . Thank you so much

lukas_tek (author)jowarkz2015-02-15

I think you need to connect the positive pin of the mic to the base of the transistor.

Lentamentalisk (author)2014-03-30

Can anyone suggest where to modify this to increase the amplification?

I am getting ~100-150mV for everything below 100dB, and at 100dB+ it rapidly rises up into the 2V range. I'd love to get some more definition in the 70-100dB range, even if I lose it in the 100+dB range.


I just answered my own question. To change the amplification, change the 100k resistor value. I believe doubling the resistance doubles the amplification.

pinst (author)2012-03-04

Could someone help a newbie add a low-pass filter to this design? I have an electret mic with a frequency response of 20-20000HZ but wish to filter out frequencies above 300HZ.


ASCAS (author)pinst2012-05-06

make a simple audio crossover.

maixy (author)2012-03-15

i have been wishing to make an amp
but i do not know too much the knowledge of electronic
i will appricate you if you can add some explanation to it

framistan (author)2011-04-22

A very usefull schematic. I am printing this out on 3x5 card and will certainly use it. thanks.

lukas_tek (author)framistan2011-04-23

thanks for you !
because you see my instructables!

oteng0914 (author)lukas_tek2011-09-07

is this the combination for the circuit of rtty21?

lukas_tek (author)oteng09142011-10-29

May be because if you want a voice in the radio station you need a pre-amp to the mic , cause the mic alone don't make sound!

jensenr30 (author)2011-04-20

this looks nice.
I should try it sometime.

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