Electret microphone question

That's a start, but it still leaves multiple possibilities.

You do have an amplified speaker connected to the second op-amp? Because the schematic shows a speaker, but it won't really drive a speaker.

The first op-amp should give a gain of a hundred, and the second stage gain up to 10, which compounded is quite a bit of gain. ONe of the stages could be wired up wrong, or isn't being coupled properly, and the gain could make up for it, even though it results in a weak signal.

You do have the non-inverting input of the second op-amp connected to something that supplies half the Vcc? The schematic doesn't show that outright, but if that 1K resistor isn't connected to 1/2 the Vcc (normally you'd have a something like two 1K resistors in series from Vcc to ground, and that 1K resistor to the non-inverting input of the second op-amp would go where the two 1K resistors are joined), then that second stage won't work properly. It will be way out of the range where it can do any amplification.

Or if that 1uF capacitor from the microphone to the first op-amp is missing, or maybe even it's in there but in reverse polarity, the power to the microphone will get to the first op-amp and mess up its operation.

Assuming you are using an amplified speaker, put its input at the output of the first op-amp, and work on that stage until things get workin. I think you should get enough gain from that stage to hear sounds from the microphone if things are working right. If it works, then you can move on to the second op-amp.

Michael

Reply to
Michael Black
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2SK3857 for example. Has a gate resistor and -protection diode integrated. If you hook up the mike with reversed polarity, it will blow the internal fet, even with 5V. I have already damaged some Knowles mikes with static discharge from handling only.
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ciao Ban
Apricale, Italy
Reply to
Ban

Actually, the speaker is a standard plug-in power computer speaker with built-in volume control. I'm assuming since it has volume control that the input is some kind of opamp stage.

Would it be better if I get the gain of the input stage a bit lower so I don't increase the overall system noise? From the texts that I've been reading, low noise design always specify a lower gain to reduce the noise figure.

Yeah, the second stage is in single supply configuration, so am biasing the non-inverting input with half of VCC.

I've also checked this capacitor aspect before hand.

This I haven't done, yet. I'll try connecting the output to the first stage.

Thanks again, Michael!

Reply to
MRW

I was trying out this circuit:

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(classic instrumentation amplifier)

The only value that I replaced was the 1.6kohm resistor to 2.2kohm.

The audio input definitely sounds cleaner if I speak directly on the mic. However, if I place a headphone with some audio playing directly above the mic, I don't hear anything out of the speakers even if I turn the speaker volume all the way up. I also tried to speak directly in front of the mic with my distance about 10 inches away from it (the same distance when speaking into my PC mic). I didn't hear anything out of the speaker.

Is this possibly a mic issue?

I'd like to be able to duplicate the mic pickup from my speaker phone or cell phone headset. With my headset, my friends sometimes complain if I have my car radio slightly up. The headset can apparently pick up the background noise better compared to just using the cellphone microphone.

Thanks!

Reply to
MRW

power supply to the micro phone is in milli-amp no external power supply required, microphone pre-amp supply will acitve the micro phone (lessthan 500mv

Reply to
THERES RAJ, BLR

on end of the terminal is grounded with microphone body, which will be negative, other terminal will be connected to input of preamp where voice data is converted to analog speaker data, power supply should be in milli amp lessthan 3v. exceeding the power supply will damage the microphone.

Reply to
THERES RAJ, BLR

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