Why doesn't this preamp for electret mic work.

ccurtis said:

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?

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ccurtis said:

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.

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More info: The inside(radio) mic is 2k ohm condenser. Does this help me in calculation of the gain and impedance of the earpiece?

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

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