[Rene Harder Mo 30. November 2009]: > I think, the idea was to build a RC filter (R4305 & C4306) with a really > low cutoff frequency to get rid of any noise introduced by the MICBIAS > line. > However, in this case R4310=0 Ohm fcut->inf (MICBIAS internal resistance > not take into account). So to get the same effect as in the current > design we would need to increase R4310 which is not possible because > this would also increase the voltage drop across R4310 and R4305. > Currently, we are already operating the microphone near the minimal > required voltage so an additional decrease will probably result in > malfunctioning of the mic.
That's why we'd better off with 2 * 1k, and in case we need we could create a R-C-R lowpass by rplacing the other 0R with a further 1k and equipping the C. A 100uF creates a AC short to GND, so we could keep the symmetrical design of 1k from big C to mic, and one 1k from micn to GND. And we still have a R-C lowpass built from the new R. If we dn't need the big-C fix, we can leave out the C and make the one R 0R. btw: 1k + 1k (+ 1k) < 2k2 + 2k2 /j
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