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/sno/ncd/ncd_internal/ncd_elec_daq/Mk_II_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...

 

[tschrama]

anyone got some 2sk152 to sell to me?

 

[jacco vermeulen]

Sure, but you can order them from Nikko for 60 Eurocents, original sony.

 

[tschrama]

Thanks .. In ordered 50 pieces... foudn them elsewhere on the net for about 5-6$ a piece anyway... the look the the ideal low noise transistor ...


Jackinnj: how about this one:

Review of Scientific Instruments ; F. Bordoni and G. V. Pallottino ; -- July 1977 -- Volume 48, Issue 7, pp. 757-761


abstract:
The sensitivity of the new generation of gravitational wave antennas to be cooled to the temperature of liquid helium is limited by the noise performance of the preamplifier. Two circuits are described that have been realized to measure the Brownian motion of a small low temperature antenna. They use a parallel arrangement of four low noise FETs (2N6550) followed by an operational amplifier to obtain an input noise that is characterized by a voltage of 0.33 nV/Hz and a current of 24 fA/Hz plus a correlated current contribution of 8 fA/Hz at 10 kHz. Review of Scientific Instruments is copyrighted by The American Institute of Physics.

Our faculty actually has a 'mini-grail' gravitational wave antenna .. maybe I should shop around that lab..

anyway....wouldn't it be cool to make a preamp cappable of measuring gravitational waves from a He cooled grail .... and then decide to measure the residu THD of my oscilator and once that has been done.. plug your MC cartridge into it.....


Back to the original question: would the NE23383B be worth exploring, our should I stock to the 2sk152 / 2sk170 ...





PS
Peranders: you're right offcourse... 10nV/sqrt should give me 160dB s/N rev 1Volt pure sine input, but this is a project is not only about that... it's about coolness too


PPS
aren't you that guy that build all those super-over-spec projects?

 

[mzzj]

and then decide to measure the residu THD of my oscilator and once that it.....


[/B]

I am intrested to know what sort of oscillator you use to get sub 1nV/hz from your oscillator?



Okay, i think its possible to get oscillator with sub 1nV/hz noise performance but combine this to -130...-140db distortion and you have quite remarkable performance...

 

[tschrama]

.. and well ... that's the plan...

I have reached -140dB THD... residual 2nd harmonic is still a problem though at -120 or about... but higher harmonics are down to -140dB where the noise is a problem.. and this is with 1/4 sec FFT .. going to 1 sec FFT things should be even better.....

When I make down to -146.. 150dB.., i would like to write an article for audioexpress...

 

[mzzj]

.. and well ... that's the plan...

When I make down to -146.. 150dB.., i would like to write an article for audioexpress...

Any additional info before that audioexpress article?

I have been scratching my head on similar subject, remains to be seen what i can get out of 4-opamp bubba oscillator instead of "standard" wien-bridge.

 

[jackinnj]

Jim Williams described such a low noise oscillator in the Linear Technology application notes -- AN-67 -- a "parts per billion" oscillator.

We can't all live in Faraday shielded rooms, however.

 

[mzzj]

Jim Williams described such a low noise oscillator in the Linear Technology application notes -- AN-67 -- a "parts per billion" oscillator.

We can't all live in Faraday shielded rooms, however.

Low distortion, yes, but how low noise it is? article said little or nothing of noise? and for me circuit doesnt look that low noise.

 

[jackinnj]

Low distortion, yes, but how low noise it is? article said little or nothing of noise? and for me circuit doesnt look that low noise.

My kids used to tell me that "ASSUME" means "you mad an *** outta me".

Williams is truely one of the old codgers of analog -- starting out when Fairchild was knee-high to a grasshopper. Even dedicated a book to Widlar.

One thus ASSUMES that 1*10e-9 means that it succesfully competes with the noise level.

please to read Mr. Williams treatise on noise measurement -- the folks who design space radio-telescopes, ultrasound equipment, sonar buoys, etc. swear by it.

 

[LineSource]

www.borbelyaudio.com


has a very well designed MC preamp that would be a good topology for a low noise amp with the RIAA feedback removed. This Borbely design uses a discrete JFET output buffer instead of a monolitic opamp.