Electret microphone amplifier music sound blinking led

Thread Starter

Grapher

Joined Sep 11, 2020
6
circuit - electret mic - fast blink led on music.png
Hello all, I hope someone could shed some light to my problem. First off I have no knowledge how to calculate resistors or other values needed in a circuit. I found the 2 left circuits online and I combined them.

The first circuit is a blinking led based on the (electret) microphone input, which works, but the microphone is not sensitive enough as I have to put it onto the speaker so it detects the music. Second problem, since I want this to be a part of an ambient light display I don't want the music that I'm playing be super loud and I want it that it's able to pick up the sound from further away - how far? maybe at least 1 meter so I can have this on my desk. It's probably important but I don't need the mic to be static free and distortion free, but it would be nice if it were for possible future projects.

This is where the second circuit comes into play, it's an amplifier circuit that also works, but with the sound level of my speakers that I feel comfortable listening my music to, it only works from 2cm away from the speaker.

Can I make some simple changes with basic components? I do have various resistors, some transistors, I can find some different value vaps if needed and I have a bunch of these electret microphones if wiring them in parallel/serial would do anything benefitial. I want to run this off of a battery, preferabbly the cr 2032 button type (I'll use a power button), and I want to get rid of the potentiometer, currently I use it so I can adjust it if I use different values resistors (it affects the "level" when the led starts blinking based on mic input).

In case anyone wonder why I changed R1 from 47k to 15k, it's because the lower resistance helps with the sound detection threshold but it is not enough. I have tested that in the first circuit and using a 10k resistor didn't work as the led was on all the time.

And the last question would be, would I need to readjust any components or power supply if I used 2 or more of same leds either in parallel/serial?
 

soyez

Joined Aug 17, 2020
51
Do you have the 10uf from pin one to 8? In the event that it worked OK with the sound info it might just not have enough increase. The elerect mics just put out a couple of 10's of millivolts, so even with the increase of 200 it may very well scarcely light your drove. adding your semiconductor to the yield would work better since it just needs .7 volts to turn on. Remember to restrict the drove current.
 

Audioguru again

Joined Oct 21, 2019
2,090
1) Your wiring is wrong.
2) The value of R1 is wrong.
3) The value of R2 that powers the mic is wrong.

1) I corrected your wiring.
2) I simulated the mic preamp with a 9V supply and a 3V supply showing that the low value of R1 turns on the transistor too much which causes severe distortion and low sensitivity. I show an increased value for R1 with less distortion and increased sensitivity.
3) The datasheet for an electret mic shows that its sensitivity is reduced when its supply voltage is less than 1.5V or 2V. An electret mic is shown to draw a current of about 0.25mA. Then with a 3V supply, Ohm's Law calculates the value of R2 to be
(3V-1.5V)/0.25mA= 6k ohms. Some electret mics need 3k ohms. 15k or 47k is much too high.

I increased the value of your C1 input capacitor for better low frequency response. The distortion when the input level is high is normal with a single transistor preamp.
 

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Thread Starter

Grapher

Joined Sep 11, 2020
6
Thank you very much for this. It didn't quite work for my setup so I changed the R2 to 2.2M and the C1 to 470nF which surprisingly picks up louder music beats from my speaker from about half a meter, but it doesn't really pick up other music elements from that distance. It is an improvement but that's enough tinkering for today.
 

Thread Starter

Grapher

Joined Sep 11, 2020
6
1) Your wiring is wrong.
2) The value of R1 is wrong.
3) The value of R2 that powers the mic is wrong.

1) I corrected your wiring.
2) I simulated the mic preamp with a 9V supply and a 3V supply showing that the low value of R1 turns on the transistor too much which causes severe distortion and low sensitivity. I show an increased value for R1 with less distortion and increased sensitivity.
3) The datasheet for an electret mic shows that its sensitivity is reduced when its supply voltage is less than 1.5V or 2V. An electret mic is shown to draw a current of about 0.25mA. Then with a 3V supply, Ohm's Law calculates the value of R2 to be
(3V-1.5V)/0.25mA= 6k ohms. Some electret mics need 3k ohms. 15k or 47k is much too high.

I increased the value of your C1 input capacitor for better low frequency response. The distortion when the input level is high is normal with a single transistor preamp.
Thank you very much for your informative reply and the changed circuitry. I'll be sure to check it out tomorrow and let yo uknow how it went.
 

Thread Starter

Grapher

Joined Sep 11, 2020
6
test circuit marked.png
@Audioguru again , so I quickly put together your version and it's not working at 3v, and at 6-9v the led does it's own thing without any noticable input from the mic (only when scratching on the mic foam). Based on that test I assume that capacitors are working (they're old from dead electronics but only ones I could find with those values) so I must have made a boo boo with the circuit interpretation? Could you point me in the right direction. Thank you for your time and help.
 

Audioguru again

Joined Oct 21, 2019
2,090
Of course your circuit does not work:
1) The 3V battery is too small (very low current).
2) The 3V battery voltage drops to 2V during its very short life which will not light many LED colors.
3) The 3V battery voltage is too low to properly power an electret mic causing a very low resistor value (your 510 ohms) to power it and the low resistor value kills the output level from the mic.
4) The preamp output coupling capacitor is missing causing the LED to short the DC output of the preamp transistor.
5) The LED driver transistor is missing.

When you add a coupling capacitor to the preamp then a 10k volume control pot reduces the preamp output levels to half (a 100k pot is better) but your extremely simple LED driver transistor circuit has an additional 15k resistor that kills more preamp output level. Even the LED driver transistor kills some preamp output level, I would replace it with a Jfet using a different circuit.

I show your wrong mic connection. The battery does not produce an audio output signal.
The 2.7k resistor is not used, it is representing the electret mic impedance.
 

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