On the second attempt my low noise amplifier for measuring regulator noise worked. It's based on a dual low noise op-amp with an overall gain of 300 (x10 followed by x30) and no signal noise of a few mVpp. The very thorough noise calculator I used suggested I should have a better noise floor so further investigation is needed.
I quickly checked a LN6206 regulator to confirm the approach and saw 1.8Vpp of amplified noise on the cro. That works out at around 6mVpp for the regulator which I might have been able to estimate with the cro itself. But now I can experiment with different noise reduction techniques and relative comparisons between regulators without having to estimate differences at that low level.
I started by trying a capacitance multiplier. I used a 10k resistor, a 1uF tantalum and a general purpose npn transistor. That reduced the noise from the LN6206 from 1.8pp to 60mVpp. That is a large reduction in regulator noise with really no effort.
73's
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