Stompbox with electret microphone

[guidoilieff]

Hi!

Im trying to do an amplifier for an electret mic but the designs I found online doesnt seem to work.
https://www.circuits-diy.com/simple-condenser-mic-preamp-circuit-using-2n3904/

Does anyone have a simple electret amplifier circuit to share?

Thanks

[Mark Hammer]

Does your mic capsule have 2 contacts or 3?

[Matthew Sanford]

Try creating a proper mic first rather than an amplifier. Jules gives so much here regarding the Alice mic that he, Homero, and others of the Mic Builders group have created. Many different versions too, such as the Simple P48 (I think this is it).


These are for xlr getting phantom power though, not sure it's what you're looking for

[guidoilieff]

Does your mic capsule have 2 contacts or 3?

2 contacts

[guidoilieff]

Try creating a proper mic first rather than an amplifier. Jules gives so much here regarding the Alice mic that he, Homero, and others of the Mic Builders group have created. Many different versions too, such as the Simple P48 (I think this is it).


These are for xlr getting phantom power though, not sure it's what you're looking for

HO LY!

Im trying to do a mic with cheap electret mics like this one https://i0.wp.com/makezine.com/wp-content/uploads/2014/05/electrets_web.jpg?w=834&ssl=1

nothing fancy. Just a 9v powered mic

[Matthew Sanford]

My apologies, halfway through realized I was thinking on P48. Do you have a data sheet on that capsule? Likely internal FET, make sure it's wired the right way. Ground should be the pin routed to the case.

[GibsonGM]

Have you run the output of the circuit you built into an amplifier?

Be sure it's wired correctly, on a breadboard is best. The capsule does need that first resistor which applies voltage to it, be sure there is voltage present there.  It should work.

As matthew said, be sure it is oriented correctly.

[Rob Strand]

Im trying to do an amplifier for an electret mic but the designs I found online doesnt seem to work.
https://www.circuits-diy.com/simple-condenser-mic-preamp-circuit-using-2n3904/

Does anyone have a simple electret amplifier circuit to share?

The main issue is likely to be the 27k bias resistor.  It's far too high.   Maybe try 10k.  Or better still play with the value until you get about 4.5V on the mic terminals.   The actual voltage isn't that critical as electret microphones work voltage from 1V about ground to 1V below the supply.   However with a 9V supply you don't want to go too close to 1V so that's why I suggest aiming for 4.5V.

(You could probably raise the 100k between  between the base and collector.  Maybe 1M to 2M2.)

[Nasse]

Correct me if I am wrong but I believe some capsules are not happy if the metal case is grounded, but not all the same and it is not always documented

Another useful gadget is "battery box" for electret mic

Some time ago I bought cheap electret preamp boards from Alibaba and they worked fine, cant remember what chip it was

EDIT It was ts472 chip board. Once mail ordered readymade board for Arduino with capsule and amplifier onboard but shop send me two capsules instead.

[Rob Strand]

Some time ago I bought cheap electret preamp boards from Alibaba and they worked fine, cant remember what chip it was

EDIT It was ts472 chip board. Once mail ordered readymade board for Arduino with capsule and amplifier onboard but shop send me two capsules instead

There's plenty of options for the preamp but the thing is if you don't bias the Electret capsule correctly, or at least in the ball-park, it won't work well or at all.

For the 27k to work:  Vbias = 9V, Vmic_min = 1V, R=27k, the Electret current must be less than (9-1)/27k = 300uA.    Which should (just) work for a lot of electrets but not all.  Measuring the voltage across the mic would help a lot (That's what I've called Vmic).   

Changing the base-collector resistor on the transistor would help too ; 100k isn't great.  In fact it wouldn't hurt to measure the voltage on the collector.  Maybe the build uses the wrong pin-out!