Zener Limiter Clone - Noise at -70dB(FS)

[Falk]

Hi there,

I have a Zener clone which is working right and all is good but the 2nd channel has a strange noise at -70dB.
I recorded it and raised the gain so its about -18dB in the recording.

https://www.dropbox.com/s/rqr17av4kjcits9/Zener_Noise.wav?dl=0

The input gain has no effect on the noise. When the output stage is decoupled from the input stage it is dead quite so it must be between input and output switch.

Can anyone assume where this noise comes from? I swapped pretty much every transistor in the signal path but it didnt help.
Can it be the electrolytic caps?

Regards,
Falk

 

[31cc7]

I had this kind of noise when somewhere connection to ground was missing. Maybe check if input is connected correctly? Maybe try different cable? Try different source?