I am trying to evaluate a component (OpAmp) and built this simple circuit. I didn't use a breadboard due to high capacitance and noise, I just soldered stuff over the air thinking this would be low noise.
The bench power supply I have has about 80mV output noise, the LM317 is off the shelf and has high PSRR (60db). With 100mA load (simple resistor) I see 20mV noise at the LM317 output, when I connect the OpAmp it is still 20mV. The circuit is attached together with the photo of the proto.
Why the noise on the LM317 is very high? (I change the input voltage from 7 to 40, almost no change on the output noise,btw)
What else I could do to reduce this noise to a few mV?
Is it a good idea to build this simple circuit over the air? (i.e. would it be lower noise than proper PCB)