Semisouth SJDP120R085 JFET - who's interested?

[andyjevans]

Who has used this device? There's a lot of interest over on Pass labs and a thread there, but there must also be wider interest in these new devices.

One aspect I'd like information on is using it as an equivalent to a tube device - not just as an output but also at lower current and higher voltage (200-300v) as a driver stage.

For this it would be a help to me if there were any data resembling the data provided in tube datasheets - curves, operating points, mu, "plate resistance" etc. I know it's a solid state device, but I'm wondering if it could directly replace a tube stage.

Can anyone help?

Andy

[andyjevans]

Also of interest may be the rest of the Semisouth devices

SiC Transistors | Semisouth Laboratories, Inc.

Farnell UK stock the following (only 100 and 550 are currently in stock)

SJDP120R045 Normally on
SJDP120R085 Normally on
SJEP120R063 Normally off
SJEP120R063A Normally off, Audio
SJEP120R100 Normally off
SJEP120R100A Normally off, Audio
SJEP170R550 Normally off

[Bigun]

I suspect that interest in these devices will be highest amongst the single ended class A amplifier fans. Most of these people live in the Pass forum.

Could there be value in designing a quasi-complementary class AB output with these devices ? that would likely have more interest here ?

[pieter t]

Nice PP amps could be done also with these devices when phase splitting is done before the output stage.
Look at Susan Parker and Andrea Ciuffoli's designs to give you some examples.

[andyjevans]

I know Susan and I'll have to look up Andrea - I know his tube designs. I certainly favour using interstage transformers, like Susan.

Which of these devices could be used in PP and what kind of circuit?

[pieter t]

Susan's and Andrea's design are based on follower output stages (no voltage gain; just current gain).
Susan told me that the depletion power fets have the advantage of not needing a gate voltage supply in her design because the output transformer DC resistance can be made to autobias correctly.
At the same time she suggested that it is more because of convenience than sound quality.
Her published design still uses readily available power fets (which are even used for class D amps....).
Andrea's design is an output transformerless circlotron stage; output devices would need correct positive or negative bias here (via secondary of the interstage transformer).
So I think the Semisouth devices can be used without problems when biasing is done correct; maybe someone else could advice which particular one might be best, I am not so much in that stuff.

[Bigun]

Nobody takes the bait on quasi ? I was thinking that if a quasi output could be made with p-jfet (low power) driving a power n-jfet at the bottom and a plain n-jeft at the top. Then you have complementary jfets. At low bias their transfer curves are almost square law and in theory they can have conjugate behaviour at cross-over - i.e. perfect.

[PSz.]

Have you seen this thread?

"SiC Puppy SE Amp Using Semisouth 085 JFET

[andyjevans]

Yes - it's very interesting and uses the 085 more like a tube - high supply voltage and output transformer. this is the kind of thing I would be after. I've been looking at Edcor SE transformers which have primaries going down to 150 ohms with 400mA current capacity. Looks about right, and other primaries are available. The difficulty is finding out operating points when these are as yet poorly documented, particularly at higher voltages, Nelson Pass uses his devices at lower supply voltages but they are rated for at least 1200v, which should allow them to be put into existing tube circuits.

Andy

[Shinja]

how about circlotron?