Pre-amp to Electret Mic!


Introduction: 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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29 Discussions

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?

Can i use 2n222 transistor for this circuit

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).

2 replies

... 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.

Is the output considered "line level" ?

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.

1 reply


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!

1 reply

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

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 ?

1 reply

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! ^-^

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

1 reply

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