![]() If you lower the input impedance this will help as well. You could use a high end fancy low noise opamp chip of course, but these will have a higher current consumption, and you reduce your battery life. Since this first stage has quite a high input impedance, adding more than a few dB of gain will raise the noise floor, and if you boost the treble, you may hear some hiss. You don't get anything without consequences though. For 12dB (gain of 4), Ra could be 30k, Rb would be 10k. For 9dB (gain of 2.8), Ra could be 18k, Rb would be 10k. For a gain of 1.4 (3dB), Ra could be 10k, and Rb would be 22k. So for a gain of 2 (6dB), you could use two resistors the same value, say 10k. The voltage gain is equal to (Ra + Rb) / Rb. Ra can stand on end in place of the original wire jumper, and if you make the board an extra row wider, you could easily add Rb to the left of the opamp, laying flat on the board. ![]() The second resistor (Rb) has to connect pin 2 to the Vref. One resistor (Ra) is a feedback resistor, between pins 1 and 2. For more overall gain, you can add two resistors to the first opamp stage. Click to expand.Thanks mate, I'm glad you like the project. ![]()
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March 2023
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