Electret microphone fries

[Dr.james]

Hello all,
i bought more than 10 elec.mics for my transmitters but after using it a few days, i dont get any sound out of it! (i can here a very low sound when i talk in so closer to the mic), what might be the problem? I have a 4V supply and i used 10K resistor to bias it, bls help

 

[mvs sarma]

please upload the transmitter schematic that you had used. only then perhaps, many respond to see whether the mic or some other issue with the performance.

 

[Dr.james]

ok and Does a elec.mic fry if i exceeded the voltage or current into it?

 

[mvs sarma]

you may see the internal sch of a 2 pin electret microphone on this link. https://en.wikipedia.org/wiki/Electret_microphone
with a 10K resistor in series, a 4V or even 9V power supply should not trouble you.
check whether you are connecting in reverse. one of connections is to the body of electret mic, and generally it is connected to -ve common. in such case there is utter possibility of non working but it might not damage it.

 

[Dr.james]

i know it sarma, i did connect everything just right, and do u think overy voltage/current will kill a elec.mic?

 

[mvs sarma]

it is for you to clarify what actually you connected , instead of asking will high voltage....

 

[Dr.james]

i used 4V supply voltage with 750mA Current, maybe i have connected the 4V directly into it while i do some bug fixing works on it, and also tried to solder a wire on to its body,any help?

 

[mvs sarma]

nothing should happen. the 750mA is capacity , but it would not flow thro the fet. generally FETs behave like constant current sources.

 

[audioguru]

The Jfet in an electret mic draws only 0.5mA. If it is wrongly connected directly to 9V without a series resistor then its tiny Jfet might be damaged, but I never tried it.

 

[alec_t]

Heat from the soldering attempt may have damaged it.

 

[Dr.james]

The Jfet in an electret mic draws only 0.5mA. If it is wrongly connected directly to 9V without a series resistor then its tiny Jfet might be damaged, but I never tried it.

but my supply volt is only 4V, i have about 10 e.mics laying around. All of them works but output is very low,(i can only hear the sound when i breath in very close of it)

 

[mvs sarma]

It needs amplification as you know.
please say whether any pre amp is used if so upload the sch

 

[audioguru]

A solder joint with a half-decent clean soldering iron takes only 1 second which will not fry anything.
If the soldering iron is a cheap one without temperature control then it will be way too hot and its tip will be badly corroded. It might take a long time to make a solder joint which will fry everything.

 

[Dr.james]

if a e.mic is damaged then it will not output anything even a very little amount of voice, am i right people?

 

[mvs sarma]

You did not answer my query, which Transmitter circuit did you use the electret mic? please upload that sch what you used?

 

[mvs sarma]

but my supply volt is only 4V, i have about 10 e.mics laying around. All of them works but output is very low,(i can only hear the sound when i breath in very close of it)

Your very first post said that they worked for few days. Should we take it that all the ten worked likewise for few days and then failed? when worked, whether the output was loud and clear?

 

[audioguru]

An electret mic is a small condenser mic with electret material holding a permanent 48V charge. It has a Jfet impedance converter inside that uses only 0.5mA usually through a 10k resistor from a 9V supply.

A dynamic mic is a coil and magnet mic. Applying 4V directly to it might fry it because it does not need to be powered and it has a fairly low resistance of its coil.

 

[Dr.james]

Repeat: if a e.mic is damaged then it will not output anything even a very little amount of voice, am i right people? Please answer this so i can recognize my mic is fried or not

 

[alec_t]

if a e.mic is damaged then it will not output anything even a very little amount of voice, am i right people?

It depends what damage has been done. If the FET is dead then you probably won't get any output. But if heat has reduced the electret polarisation charge then you may get a weak output.

 

[Dr.james]

How could i test them? Without using a transmitter