Oh man!
The capacitive mixer is no good! I'm tending to use the inductive mixer again. And I will leave the coupling capacitors (the output of the headphone amp should already be AC coupled - ain't it?). Frequency determining parts shouldn't be at the input of the transmitter. When I lower the capacitance values for the coupling capacitors, they became frequency determining caps in the last proposal. So damn it .
Back to the stable inductive coupling mixer.
Aziz
PS:
I'm trying to improve the power efficiency of the transmitter. The transmitter should not suck more energy from the external usb sound card. So I have to increase the TX-coils inductance a bit. This forces me to use low resonant capacitor values to get up to 70 kHz for the upper frequency range. And I get a problem with the capacitive mixer.
The capacitive mixer is no good! I'm tending to use the inductive mixer again. And I will leave the coupling capacitors (the output of the headphone amp should already be AC coupled - ain't it?). Frequency determining parts shouldn't be at the input of the transmitter. When I lower the capacitance values for the coupling capacitors, they became frequency determining caps in the last proposal. So damn it .

Back to the stable inductive coupling mixer.
Aziz
PS:
I'm trying to improve the power efficiency of the transmitter. The transmitter should not suck more energy from the external usb sound card. So I have to increase the TX-coils inductance a bit. This forces me to use low resonant capacitor values to get up to 70 kHz for the upper frequency range. And I get a problem with the capacitive mixer.
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