Electret microphone question - Page 2

EC8010 · 16th July 2007, 09:33 PM

I'm just about to design a microphone pre-amplifier for exactly the same use as you. I'll be using an electret capsule where I assume that the source of the FET in the capsule is either already disconnected from the case, or can be disconnected from the case. Op-amps will not be involved. Yes, I will post the design if it works properly.

Juergen Knoop · 17th July 2007, 12:15 AM

added a view pictures of my simple microphone
I build it after a Klang&Ton article
Monacor MCE-4000

phugger · 4th August 2007, 04:22 PM

I'm also in the process of fiddling with an electret microphone.

I am trying to repair a shotgun mic that had a broken electret capsule. The microphone body itself doesn't seem to have another amplifier so the only amplifier in the whole unit is the FET built into the electret capsule.

I replaced the capsule and biased it using the circuit on the bottom of the page zobsky pointed out. I changed the 1K resistor to 2.2K because my electret capsule said its impedance was 2.2K.

Everything seems to work but the output of the mic is very low.

Not sure if an external amp was orignally needed because this mic seems to plug direclty into the xlr jack of my camcorder.

THanks

Juergen Knoop · 4th August 2007, 04:31 PM

your camcorder should have a built-in amp, so you can connect the capsule directly.
Have you tried it without the extra circuitry?
regards

phugger · 4th August 2007, 04:42 PM

What exactly do you mean by without the extra circuitry?
Like directly hooking up the electret capsule (with the battery and biasing circuit) to the xlr jack?

I believe the microphone itself has some other circuitry inside, but i think its for the M and V switch which toggles a rolloff filter or something.

Juergen Knoop · 4th August 2007, 04:48 PM

electret capsules don't need the additional battery and biasing circuit.
As I understood, your camcorder dealt with a capsule without that before?
Then it is not necessary to add them yet.
regards

phugger · 4th August 2007, 04:58 PM

Oh, the mcirophone body itself has an AA battery, and I'm pretty sure it's used to power the electret capsule. So there has always been a battery involved in powering the capsule; before and after the repair.

Juergen Knoop · 4th August 2007, 05:24 PM

You only replaced the capsule and changed the resistor?

regards

phugger · 4th August 2007, 05:37 PM

Well, sort of.

The original capsule was a 3 pin one.
I replaced it with the circuit i mentioned earlier: a 2 pin capsule, the resistor, and a capacitor.

Juergen Knoop · 4th August 2007, 06:24 PM

perhaps 1,5V is to low for your new capsule?
I don't know.

regards

16th July 2007, 09:33 PM	#11
EC8010 diyAudio Moderator Join Date: Jan 2003 Location: Near London. UK	I'm just about to design a microphone pre-amplifier for exactly the same use as you. I'll be using an electret capsule where I assume that the source of the FET in the capsule is either already disconnected from the case, or can be disconnected from the case. Op-amps will not be involved. Yes, I will post the design if it works properly. __________________ The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...

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17th July 2007, 12:15 AM	#12
Juergen Knoop diyAudio Member Join Date: Jan 2007 Blog Entries: 3	added a view pictures of my simple microphone I build it after a Klang&Ton article Monacor MCE-4000

4th August 2007, 04:22 PM	#13
phugger diyAudio Member Join Date: Dec 2004 Location: Fairfax, VA	I'm also in the process of fiddling with an electret microphone. I am trying to repair a shotgun mic that had a broken electret capsule. The microphone body itself doesn't seem to have another amplifier so the only amplifier in the whole unit is the FET built into the electret capsule. I replaced the capsule and biased it using the circuit on the bottom of the page zobsky pointed out. I changed the 1K resistor to 2.2K because my electret capsule said its impedance was 2.2K. Everything seems to work but the output of the mic is very low. Not sure if an external amp was orignally needed because this mic seems to plug direclty into the xlr jack of my camcorder. THanks

4th August 2007, 04:31 PM	#14
Juergen Knoop diyAudio Member Join Date: Jan 2007 Blog Entries: 3	your camcorder should have a built-in amp, so you can connect the capsule directly. Have you tried it without the extra circuitry? regards

4th August 2007, 04:42 PM	#15
phugger diyAudio Member Join Date: Dec 2004 Location: Fairfax, VA	What exactly do you mean by without the extra circuitry? Like directly hooking up the electret capsule (with the battery and biasing circuit) to the xlr jack? I believe the microphone itself has some other circuitry inside, but i think its for the M and V switch which toggles a rolloff filter or something.

4th August 2007, 04:48 PM	#16
Juergen Knoop diyAudio Member Join Date: Jan 2007 Blog Entries: 3	electret capsules don't need the additional battery and biasing circuit. As I understood, your camcorder dealt with a capsule without that before? Then it is not necessary to add them yet. regards

4th August 2007, 04:58 PM	#17
phugger diyAudio Member Join Date: Dec 2004 Location: Fairfax, VA	Oh, the mcirophone body itself has an AA battery, and I'm pretty sure it's used to power the electret capsule. So there has always been a battery involved in powering the capsule; before and after the repair.

4th August 2007, 05:24 PM	#18
Juergen Knoop diyAudio Member Join Date: Jan 2007 Blog Entries: 3	You only replaced the capsule and changed the resistor? regards

4th August 2007, 05:37 PM	#19
phugger diyAudio Member Join Date: Dec 2004 Location: Fairfax, VA	Well, sort of. The original capsule was a 3 pin one. I replaced it with the circuit i mentioned earlier: a 2 pin capsule, the resistor, and a capacitor.

4th August 2007, 06:24 PM	#20
Juergen Knoop diyAudio Member Join Date: Jan 2007 Blog Entries: 3	perhaps 1,5V is to low for your new capsule? I don't know. regards

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