Hi If you have any ceramic capacitors in the mix, they are often microphonic. The X7R versions are typically the best “high C” types. NPO’s normally are completely non-microphonic. Other non-ceramic caps should be ok, but who knows.
Roughly speaking, 1 nV / Hz should be low enough to not matter. Since all these specs are “typical” one never knows quite what this or that part may be doing. You *should* see a drop putting in a 1 nV in place of a 5 nV. Bob > On Jul 12, 2022, at 7:53 AM, Erik Kaashoek <e...@kaashoek.com> wrote: > > I'm struggling with the noise floor. > First tests where done with a 5nV/sqrt(Hz) opamp. Noise floor with shorted > mixer output at 10kHz was -140dBc/Hz. Then I tried with 1nV/sqrt(Hz) opamp, > but that made no difference, noise floor at 10kHz was still -140dBc/Hz > The setup was simplified to this schematic: > http://athome.kaashoek.com/time-nuts/PNA/SSPNA.JPG > The REF_buffer creates a virtual ground, the Audio_LNA amplifies into the > differential audio output . > Why did the lower noise opamp not make a difference? > Also the setup is acting like a nice microphone. Tapping the housing is > clearly audible. Which component may be causing the microphony? > > _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
