Do low noise zeners exist?

LM329 quotes 7 μV wideband noise figure. Since when was in order of magnitude or two not a significant improvement?

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Two orders of magnitude? Check your math or look at figure 14 of the datasheet! The LM329 is 75 nV/rtHz (7.5 µV in a 10 kHz bandwidth), so either 2x better or 2x worse than the discrete Zener, depending on current.

If you find a temperature stable voltage reference which has two orders of magnitude lower noise than these figures (without filtering and at reasonable cost/complexity), make sure to get a patent before posting here...

Samuel

Samuel Groner said:

Check your math or look at figure 14 of the datasheet!

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I see. The max number isn't awfully convincing either.

The max number isn't awfully convincing either.

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Indeed! Probably more a sign that they're not testing this figure than that actual specimen are that bad. Bot not guaranteed is not guaranteed...

Samuel

If you want "low noise", you can try a BJT VBE multiplyer with the CB bypassed with a suitably large cap. For a tru-hole circuit, you could cook a SMT "thingy" that would fit in place of your Zener, imho, BC817-40 is your friend.

Caveat: Temp. stability not good, and more importantly, it will have a very "soft knee" wrt. voltage regulation. Which could be somewhat improved if you lift the BJT emitter with a diode junction or two, or a small SMT LED, but hey, we're already overdoing it, right?

Samuel Groner said:

The max number isn't awfully convincing either.

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Indeed! Probably more a sign that they're not testing this figure than that actual specimen are that bad. Bot not guaranteed is not guaranteed...

Samuel

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I had one major IC company refuse to even specify nominal noise levels for their 3 terminal voltage regulator. I only asked because their regulators were so noisy it was showing up in my audio path (long story). The other IC brands were quiet, so I black balled the outlier.

JR

RuudNL said:

Yes, that is indeed a simple solution to keep the zener noise down.
The only problem is where to place the extra components on the existing PCB... (Space is limited!)

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It's only ONE resistor.  You can move the cap across the Zener to after the resistor.

But if you wan't a really LN component to replace the Zener, try a resistor so that the voltage across it is roughly the same as as with the Zener.  I've done this on a commercial device in Jurassic times and it works well.

As long as your P48V preamp meets IEC standards 48V +/-4V until 10mA, there is no problem if that point isn't perfectly regulated.  It will vary with Idss of the FET but for a DIY one off, no big deal.

Yes, I thought of that myself. (To replace the zener with a resistor.)
The main goal is to reduce the voltage for the FET stage.
The regulation is not very important.
A voltage change of 0.2 V (or so) won't cause the FET to operate out of its workpoint.
But at the moment I am happy with the three 2.7 V zeners in series.
(I've put them zig-zag in a short piece of shrink tube and they fit on the original PCB.)

Two small TH 1.5mm (1.6?) white leds would solve your problem even in a crowded circuit, without any mechanical acrobatics, nice and sturdy. (IMHO)

Yes, you are right! I had 2.7 V zeners at hand, but no white LEDs.
I did some tests with yellow LEDs and found that they are really low noise!
But I will keep the white LED solution in mind next time.

I can't draw a picture ATM, but you could glue them back-to-back (easy if you obtain the small rectangular ones), so you would in effect "get" a comparable "lead spacing" to, say, a "box" poly cap.

Now, you'd have to solder the "upper" leads together (and if needed, wrap in a shrink-tubing), so it would look remotely similar to a - noname poly cap.

But, you could be smart and take also Ricardos advice BUT "mod it" - use a low-value SMT resistor (22-47 Ohm) an solder it across the upper LED leads, the ones which would otherwise get soldered together (i.e. shorted).

Super-glue it and shrink-wrap it, ET VOILA, super quiet photo-fancy ghetto stabilizer, DIY styley.

Mannnnng..

Like this..

This topic is very old but very interesting.  I found this article with more information about noise of different ways of regulation.
http://www.dicks-website.eu/noise_in_voltage_references/part1.html

better to keep everything in one place.

BR
Rafael

Interesting!

Rafael, your link gave me an afternoon full of reading. Great resource.