CD29 could be leaking.? Without a mic connected, the voltage on the tip should be approximately 9.9/10th of the voltage supplied to the sBitx.? That assumes a 10meg input resistance on your meter.? There should be no current draw through RD21, though I suspect you derive the current reading from the voltage drop across it.? The voltage drops when the mic is connected.
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Try disconnecting CD29 and measuring the voltage again.
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Reducing RD21 can increase the bias voltage to the mic.
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73
Evan
AC9TU
