AionFX - Ares Preamp - JFET procurement?

[box_maker_1]

Hey folks

So, between mouser and Small Bear, I've successfully found all the parts for the Ares PreAmp except for the JFETs.

Page 5 in the documentation here: https://aionfx.com/app/files/docs/ares_documentation.pdf
Gives a few options, but I wanted to get the collective wisdom about which ones to use.  Any suggestions?

I definitely plan on buying at least 5 or so of each and testing the I-dss and V-GS(off) values.

[Vivek]

I would think that it would be quite difficult to find a FET of a specific Vgsoff and Idss

Here are results of testing about 200 FET

[mozz]

Just bought a few of these boards so it was on my radar. I don't know what jfet i was planning on using but will get back to you.

[box_maker_1]

Where do you folks buy JFETs?
And if the listed ones in the documentation, what is recommended?

Thanks!

G

[Paul Marossy]

I built mine using the specified FETs, which I got off eBay some years ago.

[MikeA]

Where do you folks buy JFETs?
And if the listed ones in the documentation, what is recommended?

UTSource has both 2N5484 and 2N5485, used, TO-92 packages, for less than $1 in small quantities, with 60 day returns for any reason if they don't suit you.  I've had success with their new and used IC's from the "UTSource" seller (they also host other sellers, but UTSource usually has a pink background in the photos) meaning that they test out and function identically to known authentic parts I've sourced from Mouser, etc.   I haven't tried their other marketplace-type sellers.  I think these are the two FET part numbers that Aion recommends for Q1/Q2, with the caveat of selecting for the parameters in the build doc.

[box_maker_1]

Excellent. Thanks, I see those parts on UT source.

I'll give it a shot and report back.

[Vivek]

I think these are the two FET part numbers that Aion recommends for Q1/Q2, with the caveat of selecting for the parameters in the build doc.

In practice, it is near impossible to find an FET with a particular specified Vgsoff and Idss.

I'm not with AION if he specifies an exact Vgsoff and Idss as the only way to get that circuit to work. A wide range of acceptable parameters is the target.

In practice, I am sure a range of FET will work in that schematic without any change of parts, while a wider range will work if parts change is allowed.

[aion]

I'm not with AION if he specifies an exact Vgsoff and Idss as the only way to get that circuit to work. A wide range of acceptable parameters is the target.

The build doc just says to try to get close if you can, although close is subjective, but certainly anything +/-0.25V from the provided Vgs(off) target would be close enough. So -1V to -1.5V for Q1, and -2.5 to -3V for Q2 - and even outside that boundary it'll still work fine, they're really not doing anything special.

That said, I'm not entirely sure I buy the claims of the original builder that the JFET selection is crucial, but I just report the news... he said they're special, so I measured them and provided the data. But it's a sample size of one, so we don't have a whole lot of insight into his selection criteria.

[Vivek]

Thanks Aion. I agree with your post.


PS: great respect for your work !

[readingaregood]

Agree, respect for your work! I'm pretty new, just finished your Spectron and I learned a lot. Great documentation. Des Moines represent.