It's Friday evening, time for some
Fun with TE!
Todays star of the show: a low noise preamplifier
It's set to a gain of 1000 and limits the bandwith from 1Hz to 30kHz. We see the output on the scope and dmm.
I'll adjust the timebase to show the noise best I can but leave the sensitivity the same.
Please excuse the shoddy camera work, still fighting with it a bit. Also, sorry for the big pictures Vince.
First let's check a LM399 based voltage reference:
![](https://i.imgur.com/FpAYw2z.jpg)
Typical datasheet noise is 7µV, maxium 20µV in a bandwidth up to 10kHZ. We measure 33µV, but the circuit itself has some gain, the bandwidth is up to 30kHz and these are actually Czechoslovakian-made MAB399 clones - it's in the ballpark I'd say.
Next up, a reference based on a zener running at 5mA.
![](https://i.imgur.com/xUJzWuT.jpg)
If it weren't for some kind of
evil wiggle it would be lower noise as expected for the higher current.
I'll have to come back to this and see where that comes from
![Confused :-//](https://www.eevblog.com/forum/Smileys/default/confused0024.gif)
Number three is a low noise voltage regulator based on
https://wenzel.com/documents/finesse.html ![](https://i.imgur.com/eawT1eQ.jpg)
Now that looks more like it!
Nice and well you might say, but how noisy is the supply you are powering this with?
![](https://i.imgur.com/xjm5lUy.jpg)
Not exactly low noise, a linear supply based on LM723.
Now, what about that switching supply lurking below?
![](https://i.imgur.com/itIfd0P.jpg)
It's a switcher alright
![Laughing :-DD](https://www.eevblog.com/forum/Smileys/default/smiley_laughing.gif)
But still only 2.5 times the noise of the linear one so not too shabby (it is without load though)