J-FET low noise audio transistor not obsolete?

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pliniogbferreira

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Joined 2014
Hi,
What would be the best jfet transistor for audio applications such as preamp input stage or buffer stage?
I was searching some discrete parts to use, but I've found that BF's, 2SK's, are all obsolete now. I have to build something with not obsolete.
By the way, the transistor must be available (being produced normally, in order to be able to buy them in large amount.)

Thanks!

Plínio Ferreira
 
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pliniogbferreira

Member
Joined 2014
AndrewT, maybe I just have written the point not very clearly. But, I made my project with a N-channel jFET, BF245A and after that changed to 2SK117 or 118, but realized they were not available no more. I went with the 2SK170, but it's obsolete too.
Then I guessed the BF's and 2SK's were all obsolete, but they are not; realized that when didiet78 told me something about the LSK170.

What device (low noise audio transistors) is commonly used for such application, I say buffers, or differential stages, or microphones preamps, or bifet amp ops, or something that require a very low noise devices for amplification?

Regards,
Plínio Ferreira
 
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pliniogbferreira

Member
Joined 2014
Flavio Marins,
cheguei a dar uma olhada sim, mas em suas características, na folha de especificações, não diz ser um transistor de baixo ruido de aplicação exclusiva para áudio.
Enfim, você acha que isso seria um problema? Creio que se utilizar vários dentro do circuito, talvez pudesse ter alguma fonte de ruído bastante indesejável. Temo por resultar naquele chiadinho no fundo, que muitos amplificadores têm.

atenciosamente,
Plínio Ferreira

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Flavio Marins,

I've taken a quick look at it, but in its features in the datasheet, there's nothing that says that it's low noise audio transistor, or has audio as the main application.
Anyway, do you think this would be a problem? I believe that if you use multiple devices within the circuit, it could be, perhaps, a source of some undesirable noise. I fear for that little boring noise in the background that many amplifiers have.

Thanks!
Plínio Ferreira
 
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didiet78

Member
Joined 2007
pliniogbferreira said:
Flavio Marins,
cheguei a dar uma olhada sim, mas em suas características, na folha de especificações, não diz ser um transistor de baixo ruido de aplicação exclusiva para áudio.
Enfim, você acha que isso seria um problema? Creio que se utilizar vários dentro do circuito, talvez pudesse ter alguma fonte de ruído bastante indesejável. Temo por resultar naquele chiadinho no fundo, que muitos amplificadores têm.

atenciosamente,
Plínio Ferreira

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Flavio Marins,

I've taken a quick look at it, but in its features in the datasheet, there's nothing that says that it's low noise audio transistor, or has audio as the main application.
Anyway, do you think this would be a problem? I believe that if you use multiple devices within the circuit, it could be, perhaps, a source of some undesirable noise. I fear for that little boring noise in the background that many amplifiers have.

Thanks!
Plínio Ferreira
Click to expand...

BF862 it's low noise Fet, based on Scott Wurcer measurement.
 
scott wurcer

scott wurcer

R.I.P
Joined 2004
pliniogbferreira said:
Amerloc,
thanks for the tip!
I didn't know about interfet. They have something interesting.

didiet78,
looked for Scott Wurcer, didn't know who he was. Now if you say so, about his measurements, I trust. :D
It's really nice knowing that BF862 is a possible option of low noise fet.
Click to expand...

The data is in the PASS LABS sub-forum somewhere. More importantly lots of folks have done phono stages they are very happy with, unfortunately the best example is from a former participant.

There is possibly a dual version from another vendor but I can't find it now.
 
scott wurcer

scott wurcer

R.I.P
Joined 2004
FLAVIO MARINS said:
Plinio,
The bf861 is an option also, but... there is more details in the datasheet regarding noise corner, which is around 2Khz.

Does someone recomends the use of the Jfets in paralel in order to reduce the noise, as used in a Pass Phono Preamplifier?

Thanks,Flávio
Click to expand...

Unfortunately the noise data is next to useless, you need to risk buying a batch and verify that the low frequency noise corner is actually very low. No one I know has ever had an issue and at the price there is not much to lose. This is an RF part and they have no need to guarantee low frequency noise, OTOH current processes are so clean and controlled that the low noise comes for free.
 
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pliniogbferreira

Member
Joined 2014
scott wurcer said:
The data is in the PASS LABS sub-forum somewhere. More importantly lots of folks have done phono stages they are very happy with, unfortunately the best example is from a former participant.

There is possibly a dual version from another vendor but I can't find it now.
Click to expand...
scott wurcer said:
Unfortunately the noise data is next to useless, you need to risk buying a batch and verify that the low frequency noise corner is actually very low. No one I know has ever had an issue and at the price there is not much to lose. This is an RF part and they have no need to guarantee low frequency noise, OTOH current processes are so clean and controlled that the low noise comes for free.
Click to expand...

FLAVIO MARINS said:
Plinio,
The bf861 is an option also, but... there is more details in the datasheet regarding noise corner, which is around 2Khz.

Does someone recomends the use of the Jfets in paralel in order to reduce the noise, as used in a Pass Phono Preamplifier?

Thanks,Flávio
Click to expand...

Scott Wurcer,
Flavio Marins,
I've been looking for something about the BF862, and, I found some pretty nice measurement data around the internet. Therefore, as you can see in the figure below, it has a SO low voltage noise density (even compared to others as LSK170) that, is not just an option, but maybe one of the best options of low noise J-FET.
I guess Scott Wurcer got the point when he said about the current processes be so clean and controlled that the low noise comes for free.

Scott Wurcer, I found this post of yours:

http://www.diyaudio.com/forums/pass-labs/175040-more-fet-noise-measurements-euvl.html

is that what you refered about the data measurement? Anyway, after reading the post, you had really impressive results for a RF-FET, as you said. Indeed, people won't get any troubles with them (BF862) in low noise applications.

Another question, in intention to make a flat response condenser microphone pre-amp, would you go with BF862 or 2SK107(LSK107) or 2SK118 or both (considering, some kind of cascade amplification - two common source stages) what would be the main criteria you'd use to choose?

These data in the figure and table below is good for comparison among other FET transistors, it seems reliable.

An externally hosted image should be here but it was not working when we last tested it.


Another important data can be seen in this table:

An externally hosted image should be here but it was not working when we last tested it.


I got the images in this website:
Measurements Rate SMT Low-Voltage n-JFETs Under Consistent Conditions | Power content from Electronic Design

Thank you guys for everything, twice!! :D
______________________
Plinio Ferreira
 
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