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Jebem 19th December 2011 12:11 AM

Sonic Frontiers SFP-1 Phono Stage
2 Attachment(s)

I have this idea of using a JFET as a Phono Head Amp for my MC Lyra Lydian cartridge (500uV).
Currently I use a Musical Fidelity The PreAmp A3 (shunt power regulation, LM394 BJT matched pair head amp, and VQ1000J MOSFETs), and I want to beat it.
I know that one AD797 IC as it is based on BJT's can give better S/N ratio, but I don't like to see so many transistors in the signal path... I want a minimalist design.
And why not mix JFET with Tubes?
First time I saw this design was in the 90's from Sonic Frontiers, when I used to buy quality components from The Parts Connection.

So, I share here the Sonic Frontiers SFP-1 Phono Stage schematic (partial, due to upload space constrains) so you can comment on it.

The JFET in use are marked as J310. Anyone have information on this one?

+B1 AND +B2 = 210VDC (for the 12AT7 output tube and 6DJ8 RIAA driver)
+B3 = 187VDC (for the JFETs)

Attachment 255682

Attachment 255683


kevinkr 19th December 2011 12:38 AM

J310 is a standard N channel JFET, Fairchild amongst others currently produces it. Whether or not it is quiet enough for a 500uV cartridge will require inspection of the data sheet to determine. (Google)

Jebem 19th December 2011 10:39 AM

Yap, it doesn't look too impressive at 3dB / 6nV to 10nV per sqrtHz... I have some much quieter (and expensive ones) 2SK146 that I can get from a local supplier (New Old Stock) that can do a better job.

DF96 19th December 2011 11:51 AM

J310 makes an excellent VHF/UHF amplifier. It is an old design and may have too much 1/f noise for low-level audio.

Eli Duttman 19th December 2011 01:12 PM


For the hybrid circuitry approach, I advise you look into Allen Wright's cascode, with SS "downstairs" and a triode "upstairs". Allen, who sadly is no longer with us, used a JFET in a single ended setup and a twin BJT in a balanced setup.

AFAIK, AW's company VSE is still in business and they will sell you appropriate "sand" for the project.

Jebem 19th December 2011 01:40 PM

Thanks a lot DF96 for Your good input (by the way, I like the "D" series valves, really... I have got a few valve portable radios from eBay UK, like Bush TR82C's or the KB RHAPSODY DE LUXE PP251 to mention but a few... it reminds me when I was 6 years old and started poking around with my dad's Philips "D" series radio... ).

Thanks a lot Eli for your suggestion.
I'm learning from You that Allen has passed away... How sad. This is one big loss, as I really liked his ideas, diverging from the standard stuff. I used to visit his site some years ago, and reading his articles in Sound Practices USA magazine as well. Maybe I will test one of his circuits one of these days.

Jose Mesquita

Jebem 19th December 2011 09:27 PM

Sonic Frontiers Phono 1 Service Manual
1 Attachment(s)
OK, people, for those interested in the SFP1 guide, here is it in full glory TIFF format:
Attachment 255825


Burnedfingers 19th December 2011 09:42 PM

I only got one page of it:confused:

SY 19th December 2011 09:44 PM

Use the arrow buttons on the bottom.

Jebem 19th December 2011 10:07 PM

1 Attachment(s)
Funny, I just downloaded it now and I can see all the 22 pages of the service guide.
You need a TIFF display tool like Windows Photo Viewer.
Sorry to ask, but did You check the left and right arrows to navigate between pages?

Attachment 255826

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