On 7/13/22 5:24 AM, Dan Kemppainen via time-nuts wrote:
Erik,
Just a thought. The 7805 in your schematic appears to be a big part of
the signal chain. I've run into issues with 78xx series regulators
being noisy. Spent a few weeks chasing down noise issues in some
equipment and the 78xx regulator was a part of the problem. Replaced
it with LT3042 as part of the solution.
Also note, not all 7805's are created equal. Different vendors may be
better/worse than others.
Good luck!
Dan
+1 for the 200 mA LT3042 (and the higher current 0.5A LT3045). There are
now negative voltage versions, too, LT3094, also 0.5A.
Noise from 10Hz to 100kHz is around 0.8 microvolts. At 10 kHz 2
nV/sqrt(Hz). But the real thing these things are good at is PSRR at
higher frequencies. >70dB at 1 MHz
They have enable inputs, can be paralleled willy-nilly, etc
On 7/12/2022 9:45 PM, [email protected] 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 -- [email protected]
To unsubscribe send an email to [email protected]
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe send an email to [email protected]
