I repeated the exercise with a 78L08 and noise fell from 480mVpp to 30mVpp. Two surprises - the 78L08 was less noisy than the LN6206. I had expected it would be noisier since higher output voltages tend to have more noise for the 78Lxx parts. And apart from the 78L08 being quieter than I expected my test apparatus is not perfect.
I had expected that the capacitance multiplier would reduce noise by the same factor as it did with the LN6206 ( 30 fold, 1800mV / 60mV ). But in this case I was only getting a 16 fold reduction (480/30). I checked and the unterminated amplifier was producing ~1.5mVpp on the CRO. However, when I put a 75 ohm termination on the input BNC the noise increased to ~30mVpp. Which requires more investigation.
Still, the capacitance multiplier makes a substantial difference and will become a standard inclusion on future analogue projects.
Flush with some sort of success I put a TL431 onto the test board with no capacitors anywhere in circuit and with an approximate output of 8 volts.
There was no change in the 30mV of noise on the CRO. So while I cannot quantify how quiet a TL431 is, it appears to be a substantial improvement on the 78L08 alone. I am also unable to determine if the TL431, with capacitors, is an improvement. Or indeed if a capacitance multiplier is worthwhile.
But I'm not beaten yet.
73's
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