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Why doesn't this preamp for electret mic work.

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From what I recall, most electret mics have a fairly low output impedence, which is good. Check the specs on your mic to find out. It could be, too, that the voltage delivered to your mic by the radio is not correct for your mic. You can use a voltmeter, and with a plug inserted into the jack, measure the DC voltage coming out of the jack. Check that voltage against the voltage range required for your mic. If you still use your preamp, try cutting R2 down to 10K or less, maybe put a 10K pot in there to get the gain right.

It looks like you have to draw current from the power supplied at that jack to activate the transmitter (PTT), perhaps by putting a 2K resistor across the input in parallel with the mic with a pushbutton to switch the resistor in and out. I would expect that would be shown in the users manual for the radio. How are you planning to activate the transmitter? Maybe by enabling the VOX feature?

To activate the transmitter, I can enable the VOX then push a PTT button at the earpiece and speak, or in normal mode, just press the PTT at the radio when the earpiece is plugged to the radio and speak. There's no problem with that.
 
From what I recall, most electret mics have a fairly low output impedence, which is good. Check the specs on your mic to find out. It could be, too, that the voltage delivered to your mic by the radio is not correct for your mic. You can use a voltmeter, and with a plug inserted into the jack, measure the DC voltage coming out of the jack. Check that voltage against the voltage range required for your mic. If you still use your preamp, try cutting R2 down to 10K or less, maybe put a 10K pot in there to get the gain right.

If I reduce R2, the Ib and Ic will come closer, which will reduce the gain of the transistor, right?
 
More info: The inside(radio) mic is 2k ohm condenser. Does this help me in calculation of the gain and impedance of the earpiece?

2K is reasonable for that type of mic. Calculation of the circuit gain will not be very accurate do to the large variance in transistor beta, alone. Experiment with R2 to get the best results.

If I reduce R2, the Ib and Ic will come closer, which will reduce the gain of the transistor, right?

As Ic increases, the voltage at the collector decreases and thus the base current (due to the current through R2) will be reduced. This counteracts the increase in base current due a rise in the input signal voltage. Reducing R2 increases the amount of degenerative (negative) feedback, lowering the circuit gain.
 
Alright, I tried putting 50k trimmer at R2 and the result shows louder level of sound when the resistance is higher but still not desirable. I think the mic might have been damaged somewhat. I will buy a new one and try again.
 
Sounds reasonable, especially considering that the radio should perform okay with just the mic connected. Good luck.
 
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