Hi,
I have no idea what the operating voltage of the mic should be -- it's not my design and I'm not selling them.? I was only stating some ideas I had on what could be going wrong.? In the past there were posts about blocked mic ports etc, but these recent posts show this not to be the case.? It could be that the voltage is too high for the capsule, it could be a bad batch, or something else.
Personally I suspect that these are HT mics that are meant to be operated at lower voltages.? The bias resistor is not made for lowering the operating voltage, this is easy to see because drawing 0.5mA across a few kohm resistor is not going to drop much voltage right?? If the operating voltage is to be lowered, you could use a resistor divider network, a zener diode regulator, or a simple three terminal voltage regulator.? The high voltage, might not have damaged the capsule, it could be that the signal out of the capsule is distorted if the FET is not operating in its proper range.? Some checking would have to be done.? Earlier I mentioned some tests that might be tried.? Also a computer mic port probably provides some bias voltage and obviously has an input there so that would be another way to test.
The bias resistor is a load resistor and does not reduce your mic signal.? In fact -- up to a point -- increasing the resistor increases the voltage output of the electret capsule.? Anyway, the signal is not being taken through the resistor, but through the DC blocking cap.
73,
Mark
