Opa Alice build noise floor

[oscarhuang]

@oscarhuang : can you share the exact schematic of your circuit? In the original OPA Alice circuit, there are two elcaps that would effectively eliminate zener noise. The ones encircled in the picture.

Jan
View attachment 138829

This is a picture of my Alice OPA. I removed the zener diode. The noise is reduced a lot. Previously I found the noise level to be too high and unusable, but after removing D1 the noise decreased. But what I prefer is Mr. Rogs' OPA1641 circuit. I set the polarization voltage to around 60V. Very, very quiet, thank you Rogs for your selfless sharing.

 

[oscarhuang]

Practice is the best teacher. Here is the voltage I measured. The voltage before the 200 ohm resistor is 21.7V, and after the 200 ohm resistor it is 20.9V. So it is far lower than the limit voltage of the op amp. Even if the zener diode is removed, I don't think it will damage the op amp.

 

[Cqwet Dbdfte]

"The Phantom Menace" , sounds like a B-movie.
Supposedly sharp knee zeners have more noise than the soft ones.
A voltage surge from plug-in could be from a "race condition" between the local storage cap charging up and the current risetime on the OP amp.

 

[Matt Syson]

When working normally the 47uF caps will charge up to 12 Volts or more and then if the output cable suffers a short to ground (pin 10 for whatever reason, the charge on the cap will beforced through the output transistors inside the op amp with a reasonable chance of destroying or partially damaging them. Good engineering is to make things 'idiot/error proof' not trusting to luck.
By the way, 50 volt rated ferrite+zener line protection devices, as used on many digital line connections (filteres D sub as an example) can and do have strange partial zener effects well below 50 Volts.