low noise JFET, how about this one

[tschrama]

Hi all,

if been looking for a low noise solution for a THD meter I'm building.. how about this one: the NE23383B ?

Wouldn't this be a nice device to work with?

how about the 1/f noise? I cann't find info on that..

How do you guys feel about using such a device in a pearl-type of application?


regards,
Thijs

[peranders]

The question is how the noise is in the audio band

[runebivrin]

Not to rain on your parade, but this is a low voltage RF device. While there's no reason to believe it wouldn't work for audio, something tells me it's not what the manufacturer has in mind...

Unless, of course, you're planning on measuring the THD of you micro wave oven?

Rune

[peranders]

Have you seen Tangent's low noise preamp for purposes like yours?

http://tangentsoft.net/elec/meas-preamp/

If you are dealing with measurements it may be an idea to not overdo things. First state needed noise level based on facts. I have a hard time to believe that you'll need less the 1 uV in resolution.

If 1uV is enough <4 nV/Hz is enough.

[jackinnj]

I chose the Analog Devices SSM2019 -- available as an SOIC8 or SO20W outline for my noise measurement preamp -- is is fully differential and gain is set quite simply with one resistor. The device did not add any noise to a simple loop from the source of my Boonton 1120 analyzer (which has balanced outputs) to the single ended input. The threshold of the Boonton is about 0.0007% You could probable do one even better with some of the newer IN amps from TI.

You will find that when you get down to the microvolts and nanovolts of measurement layout becomes critical -- further -- just moving the cables creates a triboelectric effect which will influence measurements. Keilthly Instruments sells special cables just for these purposes.

For your amusement read some of the measurement articles written by Bob Pease of National Semiconductor -- how to measure picos and femtos.

[tschrama]

Thanks for the suggestions!

Indeed it seems like a RF device, but what do you think: should it be low noise down to the 1KHz region? 10Hz even?

I was dreaming about building a < 0.5nV/sqrt(HZ) amplifier.. should I stick to the 2SK170? Or BTJ, given that the Rsource is < 1KOhm...

I have a article decribing a 0.33nV/sqrtHZ JFET amplifier using 9 sony 2sk152 transistor in paralellel ... actually .. i wanna beat this thing


thanks!
Thijs

[jacco vermeulen]

Feel free to post the JFet article, Thijs.

[jackinnj]

you mean:
G M Gutt et al 1991 Supercond. Sci. Technol. 4 633-636
"An ultralow noise amplifier for superconductive detectors"

there are a lot of good low noise preamp/amp articles to be found in the superconducting and space arenas -- some of the devices which are now just finding their way to the outer regions of our solar system are based on 1990's technology.

take a look at this:
http://ewiserver.npl.washington.edu/...NCD_Preamp.pdf

[tschrama]

Yes that's the one ! ... just browsing all kinds of journals here at the university, I allready stumpled on a few articles that get me thinking that 1nV/sqrtHZ is not the limit...

[tschrama]

Nice one Jackinnj... thasnk! somewhere betwen 0.467 and 0.67 nV/sqrtHZ... but again at high frequencies only...