audioguru Posted August 28, 2013 Report Share Posted August 28, 2013 Jfet input opamps are a great improvement because they are square law devices. Their input voltage needs to be very close to the supply voltage based on Jfet VGS. Maybe 5V less. Does this opamp need a transistor bias voltage so that the bias impedance is higher than would be a resistor.Kevin, the improved and fixed project uses opamps with PNP bipolar transistor inputs, not Jfet inputs so that they work with an input voltage as low as the negative supply voltage.The input voltage of opamp U2 goes from 0V (its negative supply voltage) to +11.2V and never goes as high as the positive supply where it will have its output saturated as high as it can go. Quote Link to comment Share on other sites More sharing options...
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