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The upper limit to the gain setting feedback resistor value in a transimpedance amp is dictated by op amp rail voltage but is there lower limiting factor for the value also?
I changed this feedback resistor value to a much lower value in an audio DAC with very high current output (~30mA), this reduced max gain to safe levels as desired but caused caused severe distortion and I'd like to learn why.
Op amp is OPA1612, the recommended op amp in DAC's datasheet.
DAC is AK4499
The op amp input can only sink or source so much current, equally the amount decreases as it approaches the supply rails, (there is a resistance in the output),
Once it reaches the point where it cannot swing any closer to the supply rail due to that resistance, you get distortion.
edit: if your signal is bidirectional, there may also be cross over distortion, with these current levels its not an easy issue to work around, and may be improved by choosing an alternative op amp.
If you want lowest distortion, you need to identify the SHORT CIRCUIT OUTPUT of the opamp, per the datasheet, and then operate at 25% or 33% of that value at MOST.
Why?
The protection circuits are not precise, and they usually involve bipolar junctions and bipolar transistors that START TO TURNON. In STARTING TO TURNON, the gain of the opamp is impaired and the distortion soars.
